Development of Highly Durable Antifogging Materials Based on
Polysilsesquioxane with Hydrophilic Groups（親水基を有するポリシルセスキオキサンをベースとした高耐久性
防曇材料の開発）

March, 2023

Tetsuya Maeda

Hiroshima University

Contents
Chapter 1: Introduction ............................................................................................................. 1
1.
Introduction to antifogging materials .................................................................................. 1
2.
Antifogging materials ........................................................................................................ 2
2.1 Superhydrophilic antifogging material ........................................................................ 2
2.2 Superhydrophobic antifogging material ....................................................................... 3
2.3 Water-absorbing antifogging material ......................................................................... 33.
Performance required for water-absorbing antifogging material ............................................ 4
3.1 Water uptake ............................................................................................................. 4
3.2 Scratch resistance ...................................................................................................... 6
3.3 Environment resistance .............................................................................................. 7
4.
Polysilsesquioxane (PSQ) .................................................................................................. 8
4.1 Synthesis of PSQ ...................................................................................................... 8
4.2 Characterization of PSQ ............................................................................................ 9
4.3 Application of PSQ to antifogging materials .............................................................. 11
5.
Overview of this thesis .................................................................................................... 11
6.
References ..................................................................................................................... 16
Chapter 2: Antifogging Polysilsesquioxane Film Containing an Amino Group with High Scratch
Resistance ............................................................................................................................... 22
1.
Introduction .................................................................................................................... 22
2.
Experimental .................................................................................................................. 23
2.1 Materials ................................................................................................................ 23
2.2 Synthesis of poly(3-(2-aminoethylaminopropyl)silsesquioxane) (PAEAPS) ................. 23
2.3 Synthesis of poly(3-aminopropyl)silsesquioxane (PAPS) ............................................ 23
2.4 Preparation of film coatings ..................................................................................... 23
2.5 Characterization ...................................................................................................... 24
3.
Results and discussion ..................................................................................................... 25
3.1 Synthesis of amino-functionalized polysilsesquioxane ................................................ 25
3.2 Preparation of polysilsesquioxane films .................................................................... 29
3.3 XRD analysis of PAPS and PAEAPS films ................................................................ 31
3.4 Transparency of PAEAPS films ................................................................................ 33
3.5 Antifogging abilities of PAPS and PAEAPS films ...................................................... 34
3.6 Thermal stability of PAPS and PAEAPS films ........................................................... 37
3.7 Mechanical properties of PAPS and PAEAPS films .................................................... 38
4.
Conclusions .................................................................................................................... 41
5.
References ..................................................................................................................... 42
Chapter 3: Enhancing Antifogging Property of Polysilsesquioxane Film via an Amine
Hydrochloride Salt ................................................................................................................... 44
1.
Introduction .................................................................................................................... 44
2.
Experimental .................................................................................................................. 45
2.1 Materials ................................................................................................................ 45
2.2 Measurements ......................................................................................................... 45
2.3 Preparation of poly[3-(2-aminoethylamino)propyl-co-methyl]silsesquioxane (P(AEAPco-Me)S) ........................................................................................................................ 46
2.4 Preparation of poly[3-(2-aminoethylamino)propyl]silsesquioxane hydrochloride(PAEAPS-Cl) and poly[3-(2-aminoethylamino)propyl-co-methyl]silsesquioxane hydrochloride(P(AEAP-co-Me)S-Cl) films by the immersion method...................................................... 47
2.5 Synthesis of PAEAPS-Cl by the reaction of PAEAPS with HCl ................................... 47
2.6 Preparation of the PAEAPS-Cl film by the coating method ......................................... 48
3.
Results and discussion ..................................................................................................... 48
3.1 Preparation of the PAEAPS-Cl film by the immersion method .................................... 48
3.2 Synthesis of PAEAPS-Cl and preparation of the PAEAPS-Cl film by the coating
method ........................................................................................................................... 51
3.3 Synthesis of P(AEAP-co-Me)S and preparation of the P(AEAP-co-Me)S-Cl film by theimmersion method .......................................................................................................... 53
3.4 Antifogging and mechanical properties of the PAEAPS-Cl and P(AEAP-co-Me)S-Cl films

4.
5.

and its stability against water vapor .................................................................................. 55
Conclusions .................................................................................................................... 63
References ..................................................................................................................... 65

Chapter 4: Highly Transparent Antifogging Materials Based on Polysilsesquioxane Containing a
Hydroxy Group ....................................................................................................................... 66
1.
Introduction .................................................................................................................... 66
2.
Experimental .................................................................................................................. 67
2.1 Materials ................................................................................................................ 67
2.2 Synthesis of poly(glycidyloxypropyl)silsesquioxane (PGPS) by hydrolysis andpolycondensation ............................................................................................................ 67
2.3 Preparation of poly(3-(2,3-dihydroxypropoxypropyl)silsesquioxane) (PSQ-OH) film via
route A........................................................................................................................... 68
2.4 Preparation of PSQ-OH film via route B ................................................................... 68
2.5 Measurements ......................................................................................................... 69
3.
Results and discussion ..................................................................................................... 69
3.1 Synthesis of PGPS by hydrolysis and polycondensation ............................................. 69
3.2 Preparation of PSQ-OH film via route A ................................................................... 73
3.3 Preparation of PSQ-OH film via route B ................................................................... 76
3.4 Antifogging and mechanical properties of PSQ-OH film via routes A and B ................ 79
3.5 Surface morphology and transparency of PSQ-OH film prepared via route B ............... 83
4.
Conclusions .................................................................................................................... 84
5.
Reference ....................................................................................................................... 86
Chapter 5: Highly Durable Antifogging Polysilsesquioxane Film Containing Tetraethylene Glycol
Chains..................................................................................................................................... 87
1.
Introduction .................................................................................................................... 87
2.
Experimental .................................................................................................................. 88
2.1 Materials ................................................................................................................ 88
2.2 Synthesis of tetraethyleneglycol diallylether (TEGDAE) ............................................ 88
2.3 Synthesis of tetraethylene glycol bis(triethoxysilylpropyl) ether (BTESP-EG) .............. 89
2.4 Synthesis of poly(glycidyloxypropyl-co-tetraethylene glycol)silsesquioxane (PSQGly/EG) ......................................................................................................................... 89
2.5 Preparation of poly[3-(2,3-dihydroxypropoxypropyl)-co-tetraethylene
glycol]silsesquioxane (PSQ-Diol/EG) film ........................................................................ 90
2.6 Measurements ......................................................................................................... 90
3.
Results and discussion ..................................................................................................... 91
3.1 Synthesis of PSQ-Gly/EG by hydrolysis/polycondensation reaction ............................ 91
3.2 Preparation of PSQ-Diol/EG film ............................................................................. 95
3.3 Antifogging and mechanical property of PSQ-Diol/EG film........................................ 98
3.4 Durability of PSQ-Diol/EG film on humidity and temperature change ....................... 101
4.
Conclusions .................................................................................................................. 106
5.
References ................................................................................................................... 107
Chapter 6: Summary ............................................................................................................. 108
List of publications ................................................................................................................ 111
Acknowledgments .................................................................................................................. 112

Chapter 1: Introduction
1.

Introduction to antifogging materials

In recent years, antifogging materials have been attracting attention to prevent fogging on the solid
surface. Fogging occurs when atmospheric moisture in the air condenses and water droplets with adiameter of 190 nm (half of the shortest wavelength of visible light) or longer adhere to the solid
surfaces (Figure 1) [1-4]. Fogging on the solid surface scatters light and significantly reducestransparency and results in the poor optical performance of transparent and optical materials such as
eyeglasses, goggles, solar cells, microscopes, camera lenses, mirrors, automobile windshields,
headlamps and other display devices [5-13]. Fogging is a serious problem affecting not only a daily
comfort but also a safe life. In surgical treatment, the fogging at the lens tip of the medical endoscopes
may be life-threatening [14]. In windshields of vehicles, fogging may cause serious traffic accidents
due to a reduction in the driver’s visibility [15, 16].

Figure 1. Mechanism of fogging occurrence.

Considering global warming and CO2 emission, fogging has a negative effect on energy efficiency.
In solar cells, fogging induces light scattering and reduces the amount of power produced [7, 17]. A
standard method for preventing fogging in vehicles is to warm the cold air outside by a heater, and the1warmed and dried air is blown to the windshield to prevent fogging [18]. Operation of the defogger
system, however, requires large energy consumption, leading to lower cruising distance when the
defogger system is activated. This is more serious for electric vehicles that cannot utilize the waste
heat from the engine [19], compared with internal combustion engine vehicles [20]. Therefore, afacility that can reduce the energy consumption for the defogger system is desired in electric vehicles.
Consequently, antifogging materials have drawn attention because they can remarkably reduce theenergy consumption of antifogging systems, including the defogger and a hot wire on the windshields
surface.

2.

Antifogging materials

There are three types of antifogging materials: (1) superhydrophilic material, (2) superhydrophobic
material, and (3) water-absorbing material, as shown in Figure 2.

Figure 2. Antifogging mechanism of each antifogging material. (1) superhydrophilic material, (2)superhydrophobic material, and (3) water-absorbing material.

2.1 Superhydrophilic antifogging material
In the superhydrophilic material, water droplets on the superhydrophilic surface with a water contact2

angle (CA) of less than 5° spread over the surface and form a thin water layer to prevent light scattering.
For example, inorganic oxides such as titanium oxide (TiO2) and silicon oxide (SiO2) have beenstudied [21-24]. TiO2 film exhibits superhydrophilicity after ultraviolet (UV) irradiation, because theconcentration of OH groups on the TiO2 surface increases by UV irradiation [25], and exhibit excellent
antifogging properties. However, TiO2 films quickly become hydrophobic in the dark, limiting theirapplication [26]. Furthermore, the thin water layer formed on the surface of hydrophilic materials isfrozen below the freezing point, resulting in a significant loss of transparency and limiting theirapplication in environments exposed to freezing temperatures [1].

2.2 Superhydrophobic antifogging material
In the superhydrophobic antifogging material with water contact angles exceeding 150°, water
droplets are repelled on the surface. Bio-inspired by the characteristic microstructure of mosquito eyes
and lotus leaf, superhydrophobic antifogging material that combined nanoscale surface roughness andlow surface energy has been studied [1, 2, 27, 28]. Micro/nano roughness films were fabricated by
combining polydimethylsiloxane and silicon dioxide [27]. This surface exhibited excellent
superhydrophobic antifogging performance with a water contact angle of 158°. However, thesuperhydrophobicity typically originates from the nanoscale surface roughness arising from thecharacteristic microstructure, leading to poor mechanical strength and transparency. Therefore, theapplication of superhydrophobic material as antifogging material is limited.

2.3 Water-absorbing antifogging material
Water droplets are quickly absorbed into the water-absorbing material, exhibiting antifogging
properties. The water-absorbing antifogging materials have been extensively studied to overcome thedisadvantages of superhydrophilic and superhydrophobic materials. The water-absorbing materials
3

have been reported to exhibit high antifogging properties by rapidly absorbing water in hydrophilicpolymers containing hydrophilic functional groups such as hydroxyl groups, carboxyl groups, andethylene glycol [3]. They include poly(acrylic acid) (PAA)/poly(vinyl alcohol) (PVA) [29, 30],
PAA/poly(ethyleneimine)[31],

PVA/Nafion[32],

poly(ethylene

glycol)

[33],

and

poly(vinylpyrrolidone) [34]. The absorbed waters in hydrophilic polymers exist as nonfreezing water
via strong hydrogen bonding [29]. The disadvantage of water-absorbing polymer films typically is low
scratch resistance [30, 31]. The advantage and disadvantage of three types of antifogging materials are
summarized in Table 1. This thesis focuses on the water-absorbing antifogging material, which isconsidered to have a wide range of applications.

Table 1. The advantages and disadvantages of three types of antifogging materials
Type of

Examples ofantifogging material

antifogging material

Superhydrophilic

TiO2, SiO2

Advantage

Disadvantage

High antifogging

Restrictions on use inmaterial
Superhydrophobic

specific environments
Polysiloxane

No freezing

material
Water-absorbing
material3.

Low mechanical strength
Low transparency

PVA, PAAHigh antifogging

Low scratch resistanceNo freezing

Performance required for water-absorbing antifogging material

As mentioned above, water-absorbing antifogging materials have attracted much attention in recent
years, and numerous reported examples exist. Typical performance of water-absorbing antifogging
materials and their respective issues are described below.

3.1 Water uptake
Numerous studies in recent years have improved the water uptake of water-absorbing antifogging
4

material because the more significant capacity to absorb water into the material, the higher the
antifogging performance. The content of these studies can be outlined in a model equation for theswelling ratio of polymer. Various model equations have been discussed to express the swelling ratioof polymers and Flory's theory is known as one of the representative model equations [35]. According
to Flory’s theory, the water uptake of the polymer is related to the crosslinking density, ionic osmoticpressure, and affinity of the polymer with water. The swelling ratio Q can be expressed by Equation
(1).

(1)

Q: water absorption, Ve/V0: crosslinking density of polymer, (1/2 - X1)/V1: interaction between polymer
and solution, i/Vu: fixed charge per unit volume of polymer, S: ionic strength of external solution

Previous research on achieving high water uptake in water-absorbing antifogging materials has been
carried out regarding three factors of Flory's theory. Concerning water affinity of the polymer, almost
all water-absorbing antifogging materials have polar hydrophilic functional groups such as hydroxyl
groups, carboxyl groups, and ethylene glycol to interact with water molecules through hydrogenbonding and dipole interaction [29-33]. For ionic osmotic pressure, ionic unis such as ammonium
chloride and sulfobetaine that have stronger interaction with water than neutral polar functional groups
are introduced into the polymer structure [36, 37]. For crosslinking density, highly crosslinked
polymers limit the amount of water absorbed into the polymer material because the higher crosslinking
density results in the less swelling of polymer. Therefore, linear polymers such as PVA and PAA,
5

which are not crosslinked structures, are often used for antifogging materials [29-32]. These
considerations indicate that the water uptake can be controlled by appropriately designing thehydrophilic groups and crosslinking structure. However, material design based on the Flory's theory
often involves a trade-off between water uptake and durability such as scratch resistance andenvironment resistance.

3.2 Scratch resistance
As mentioned above, polymers without a crosslinked structure, such as PVA and PAA, have highantifogging performance due to their high water uptake. However, their practical application has beendifficult due to low scratch resistance, which causes deterioration in transparency and antifogging
properties after long-term use [32]. Therefore, many studies have discussed previously thedevelopment of new antifogging materials with high scratch resistance.
Hydrophilic organic polymers containing silica nanofillers have been investigated to improve thescratch resistance of antifogging materials [38, 39]. For example, adding SiO2 filler into PVA canenhance the scratch resistance [5]. However, the addition of filler sometimes suppresses theantifogging performance that is usually in a trade-off relationship with the scratch resistance.
Furthermore, silica nanoparticles' aggregation may reduce the transparency of antifogging films.
Self-healing materials that heal scratches by external stimuli such as heat, solvents, and light havebeen well studied recently and the self-healing property can improve the scratch resistance ofhydrophilic organic polymers with low cross-linked structures [40-42]. Antifogging materials with
self-healing ability often contain non-covalent bonding; e.g., electrostatic interactions and hydrogenbonds [43-46]. For example, antifogging copolymers based on poly(sulfobetaine methacrylate)(PSBMA) and poly(2-hydroxyethyl methacrylate) (PHEMA) can quickly heal scratches in thepresence of water [43]. As the copolymer of PSBMA and PHEMA absorbs water, the electrostatic
6interactions and hydrogen bonds between the PSBMA and PHEMA components weaken, and themobility of each component increases, allowing them to diffuse easily into the scratched area.
However, the healing ability of many self-healing polymers is highly dependent on the environment
in which they are used because they require external stimuli to heal.
As described above, there are few reports of antifogging materials that have both high water uptake
and scratch resistance, and breakthrough achievement is required to develop those materials.

3.3 Environment resistanceThe durability of antifogging materials is essential for realizing practical applications. However,antifogging materials may deteriorate by chemical and physical changes caused by external factors
such as heat and moisture, leading to the reduction of performances. For example, coloration is causedby oxidation, increasing the absorption in the visible light region. Additionally, physical propertychanges such as embrittlement due to chemical degradation cause cracks and an increase of surface
roughness, leading to visible light scattering. These decreases in transparency cause issues in practicalapplications, for example, that of automobile windshield endangers the driver. Therefore, thedevelopment of antifogging materials that are stable under practical conditions is of high necessity. In
particular, degradation due to chemical changes are often caused by hydrophilic groups. For example,
the hydrophilic groups may accelerate the hydrolysis reaction of the main chain[47, 48]. Therefore, it
is important to select appropriate hydrophilic groups to ensure environmental resistance.

7

4.

Polysilsesquioxane (PSQ)

Organic-inorganic hybrid materials attract recent attention for the development of unconventional
materials by combining both the properties of soft materials (rubber, gels, plastics) and hard materials(metals, ceramics, glass) synergistically [49-52]. They have, for instance, the high mechanical strengthof inorganic materials and the flexibility of organic materials. Polysilsesquioxane (PSQ) is known asa typical organic-inorganic hybrid material, in which the inorganic Si-O-Si bonds and organic
functional groups in the PSQ framework provide high mechanical strength and the high hydrophilicity,respectively (Figure 3) [53-55]. PSQ is readily processible to form film due to high solubility inorganic solvents [56-59] and the films are used in a wide range of applications, such as opticalmaterials [58], abrasion resistant coating [59], anti-reflective coating [60], antibacterial/antifungal
coatings [61] low-dielectric materials [62], dielectric layer for organic field-effect transistor [63]. In
this study, the author focuses the attention on PSQ as robust antifogging materials.

Figure 3. Structure and preparation of PSQ.

4.1 Synthesis of PSQ
PSQs are usually synthesized from alkoxysilane by the sol-gel process consisting of hydrolysis andcondensation reactions forming the sol, followed by gelation of the sol (Figure 3) [64]. First, a solution
composed of four raw materials is prepared. (1) Alkoxysilane with a selected organic group thatprovides the desired function, (2) Water for hydrolysis of alkoxysilane, (3) Solvent, and (4) Acid orbase catalyst if necessary. Then, bulk, fiber, and thin films can be prepared by calcination of the8resultant sol after processing [58-63, 65, 66].
Hydrolysis and condensation reactions proceed by different mechanisms under acidic and basic
conditions [67, 68]. In the hydrolysis reaction, there are differences in the reaction mechanism
depending the catalyst used i.e., acidic or basic catalysts. Under the acidic conditions, the hydrolysis
reaction giving silanol is promoted by nucleophilic attack of water with the oxonium intermediate ofalkoxysilane, while hydroxide anion attacks the alkoxysilane under the basic conditions. In thecondensation of silanol to form siloxane, the oxonium intermediate of silanol is attacked by anothersilanol unit under the acidic conditions, while the nucleophilic reaction of silanol anion with silanol isinvolved under the basic conditions. Because the reaction rate differs from each other under the acidand basic conditions, polymers with different shapes, such as linear polymers, crosslinked polymers,
and spherical particles, are produced depending on the reaction conditions. Therefore, to obtain thedesired polymer structure, the reaction conditions must be designed appropriately. For example, themethod reported by Abe et al successfully prepared a variety of polysilsesquioxanes with controlled
molecular weight by conducting the polycondensation reaction of triethoxysilanes under a nitrogenflow to remove ethanol while expelling the acid catalyst after only hydrolysis proceeds at low
temperature [69].

4.2 Characterization of PSQ
Characterization of PSQs is essential for understanding the relationship between their physicalproperties, reactivities, structures and applications, thus gaining insights for designing new materials.
1H and 29Si nuclear magnetic resonance (NMR) spectroscopy is a standard spectroscopic method toanalyze the structures of PSQs [70-76] by the chemical shifts that reflect the chemical environment of
atoms. 1H-NMR is often measured to estimate the consumption of alkoxy groups (degree of hydrolysis
reaction) by the sol-gel process. For example, the 1H-NMR peak derived from the methoxy group9

around 3.5 ppm was reduced by the sol-gel process of trimethoxymethylsilanes. The progress of thehydrolysis reaction was calculated by comparing the integral ratios of the peaks of methyl and methoxy
protons during the reaction course [75]. In the 29Si-NMR, peaks are clearly separated by the numberof Si bonded to OSi groups in the range of -60 to -120 ppm. For example, in the case of PSQ
synthesized from methyltrialkoxysilane, the chemical shifts of T0, T1, T2, and T3 (numbers
superscripted indicate the numbers of OSi bounded to the Si) are observed at -37 to -42 ppm, -47 to-51 ppm, -53 to -57 ppm, and -61 to -66 ppm, respectively [56, 57, 76]. V. Reschke et al reported theassignments of 29Si-NMR signals of poly(methoxymethyl)siloxane as shown in Figure 4 [77].

Figure 4.

29Si-NMR spectra of the poly(methoxymethyl) siloxane. Reprinted from "Rheology andcrosslinking of a low-viscosity SiOC preceramic polymer “, Vol 42, V. Reschke et al., p7623,
Copyright 2016, with permission from Elsevier.

Infrared (IR) absorption measurements can identify substances and analyze their states by observing
atomic vibrations in molecules [78, 79], which can be performed in all states, from monomer topolymer and from liquid to solid obtained during the sol-gel process. For example, the Si-OH-derived
10

peak near 950 cm-1 in a PSQ film gradually decreases as the silanol condensation proceeds when thetemperature is elevated from 350 °C to 900 °C [78]. This indicates that the progress of the Si-OH
condensation reaction can be analyzed quantitatively by IR measurement. GPC (Gel Permeation
Chromatography) is a method of separating analytes by molecular size using a column with pores, andcan measure the relative molecular weight of polymers to estimate the degree of progress of thecondensation reaction. X-ray diffraction (XRD) measurements can identify and quantify the
crystallization degrees and crystal structures, such as rod, ladder, and cage structures in PSQs [80, 81].
For example, PSQ with ammonium chloride groups (PSQ-NH3+Cl-) give the diffraction peaks withthe d-values consistent with the hexagonal stacking of rod-like polymers [80].

4.3 Application of PSQ to antifogging materials
Research on antifogging materials based on PSQ has been limited. In previous works, copolymers ofpolyhedral oligomeric silsesquioxane (POSS) and poly(2-(dimethylamino)-ethyl methacrylate)-blockpoly(sulfobetaine methacrylate) exhibited excellent antifogging and anti-icing properties [82, 83].
This is because hydrophobic POSS groups aggregate on the film surface to form a self-lubricating
aqueous layer by nonfreezable bound water on the surface. In addition, a POSS-linking polyamide
was reported to exhibit good antifogging properties and high surface hardness [84]. The high surface
hardness of this polymer film was likely due to the crosslinked structure and the rigidity of the POSS
structure. However, the mechanism of effects of the siloxane network in PSQ on the scratch resistance
was not adequately discussed.

5.

Overview of this thesis

As described above, various studies have been conducted on water-absorbing antifogging materials
to improve both water uptake and scratch resistance, which are usually in a trade-off relationship.
11

However, few reports succeeded in the development of high performance antifogging materials withhigh water uptake and scratch resistance. In this thesis, the author focuses on the antifogging materials
based on PSQ containing hydrophilic groups. The effects of PSQ structures on the water uptake andscratch resistance was investigated in detail. In addition, considering the practical application of PSQ
antifogging materials, the improvement of environmental resistance by designing the PSQ structures
was also examined.
In Chapter 2, to investigate the potential of amine units as hydrophilic groups, solid films of poly(3aminopropyl)silsesquioxane(PAPS)

andpoly(3-(2-aminoethylaminopropyl)silsesquioxane)(PAEAPS) were prepared on glass substrate by a sol-gel process, and their performance was evaluated(Figure 5). Furthermore, the mechanism of high scratch resistance of the PSQ films was discussed incomparison with PVA films based on the mechanical property measurement using a nanoindenter.

Figure 5. Schematic diagram of PAEAPS film (Chapter 2).

Chapter 3 is focused on the amine hydrochloride salt as a hydrophilic group in PSQ. It is expectedthat the stronger interaction of ionic units with water than neutral polar groups leads to thedevelopment of the higher performance-antifogging materials, as discussed in Equation (1). Therefore,
PAEAPS film was immersed in a 0.5 mol/L hydrochloric acid (HCl) methanolic solution to preparepoly(3-(2-aminoethylamino)propyl)silsesquioxane hydrochloride (PAEAPS-Cl) film containing
12

amine hydrochloride salt units (Figure 6). The influence of amine hydrochloride salt on theantifogging properties and scratch resistance was investigated. In addition, the durability of PAEAPS
and PAEAPS-Cl films under high humidity environments is also investigated to realize the practicalapplication.

Figure 6. Schematic diagram of PAEAPS-Cl (Chapter 3).

PAEAPS and PAEAPS-Cl films were light yellow and decreased in the short wavelength range. The
author hypothesized that the mechanism of yellowing was due to the oxidation of amino groups andamine hydrochloride.
In Chapter 4, hydroxyl groups are focused as hydrophilic groups in PSQ. In Chapter 2, the synthesisof amino-containing PSQs is described. Although the amino-containing PSQs show high water uptake
with desirable scratch resistance, the PSQ films turn yellow upon calcination. Hydrophilic organic
polymers with hydroxyl groups, such as PVA, have been widely studied and do not undergo coloration
unlike polymers with amino groups. This inspired the author to prepare PSQ with hydroxy groups as
colorless antifogging materials. However, synthesizing PSQ films containing hydroxyl groups isdifficult due to possible side reactions between silanol and hydroxyl groups. To suppress the side
reactions and to obtain a PSQ with a high concentration of hydroxyl groups (PSQ-OH), a new synthetic
strategy including the preparation of PSQ with epoxy units and its hydrolysis has been developed(Figure 7).
13

Figure 7. Schematic diagram of PSQ-OH film (Chapter 4).

Under high humidity conditions, the surface smoothness of the PSQ-OH film was significantly
reduced due to surface cracking, resulting in reduced transparency. Furthermore, the water uptake of
the PSQ-OH film was found to decrease by the durability test with repeated exposure of the film tohigh and low humidity environments. The author hypothesizes that this is due to the increasedhydrophobicity of PSQ caused by polycondensation of silanols forming siloxanes in PSQ.
In

Chapter

5,organicallybridged

PSQ

synthesized

fromtetraethylene

glycolbis(triethoxysilylpropyl)ether is described, aiming to suppress the polycondensation reaction of silanolgroups due to the space effects of tetraethylene glycol units that sterically separate the silanol groups(Figure 8). A poly[3-(2,3-dihydroxypropoxypropyl)-co-tetraethylene glycol]silsesquioxane (PSQDiol/EG) film was prepared via the sol-gel reaction of 3-glycidyloxypropyltrimethoxysilane (GPTMS)
and tetraethylene glycol bis(triethoxysilylpropyl)ether (BTESP-EG). The effects of introducing
tetraethylene glycol chains into PSQ-OH films on the durability under high humidity conditions are
discussed.
Finally, in Chapter 6, the conclusions of this thesis are described.

14

Figure 8. Schematic diagram of PSQ-Diol/EG film (Chapter 5).

15

6.

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21

Chapter 2: Antifogging Polysilsesquioxane Film Containing an Amino
Group with High Scratch Resistance
1. Introduction
As described in Chapter 1, polysilsesquioxanes (PSQ) are organic−inorganic hybrid materials thatconsist of a siloxane network with organic functional groups covalently linked to the silicon atoms [15]. The properties of organic−inorganic hybrid materials based on polysilsesquioxanes depend on thesiloxane network structure and the choice of the organic functional group, where the inorganic
Si−O−Si network structure provides thermal and mechanical stability and the organic functional groupmay be chosen depending on the intended application of the material [1]. Thus, a polysilsesquioxanewith appropriate organic groups may be a good antifogging coating material because
polysilsesquioxane films typically exhibit high scratch resistance and good transparency. However,films prepared from typical poly(alkylsilsesquioxane)s exhibit high water contact angles because thealkyl group covalently linked to the silicone atom is hydrophobic [6-9]. However, the author
anticipated that a polysilsesquioxane prepared from a trialkoxysilane bearing a hydrophilic aminogroup would exhibit both high scratch resistance and hydrophilicity imparted by the siloxane networkand the amino groups, respectively. Accordingly, in this chapter, the author describes the preparationof poly(3-aminopropyl)silsesquioxane (PAPS) and poly(3-(2-aminoethylaminopropyl)silsesquioxane)(PAEAPS) by sol−gel reactions of aminofunctionalized trialkoxysilanes and the antifogging andmechanical properties of the PSQ films. Furthermore, the mechanism of high scratch resistance of the
PSQ films is discussed based on the difference in scratch behavior between poly(vinyl alcohol) (PVA)and PAEAPS films by the nanoscratch test.

22

2. Experimental
2.1 Materials
3-Aminopropyltriethoxysilane, 3-(2-aminoethylamino)propyltriethoxysilane, and poly(vinyl
alcohol) (n = ca. 2000; degree of saponification = ca. 80 mol%) were purchased from Tokyo Chemical
Industry Co., Ltd. and used as received. Ethanol (super dehydrated) was purchased from FUJIFILM
Wako Pure Chemical Co., Ltd. and used as received. All other solvents were of the highest grade
commercially available and used without further purification. The water used for the sol-gel reaction
was purified by a Millipore Mill-Q UV system and had a resistance of 18.2 M cm.
2.2 Synthesis of poly(3-(2-aminoethylaminopropyl)silsesquioxane) (PAEAPS)In a 100 mL round-bottom flask, 3-(2-aminoethylaminopropyl)triethoxysilane (2.649 g, 10.00mmol) and ethanol (4.605 g, 100.0 mmol) were mixed and cooled using an ice bath. Water (0.5411 g,
30.00 mmol) was slowly added and the reaction mixture was stirred at 0 C for 10 min. Then, thereaction mixture was stirred at room temperature for 10 min and refluxed for 5 h. Finally, ethanol was
removed under reduced pressure at 60 C to obtain PAEAPS as a viscous liquid. The obtained PAEAPS
was diluted with ethanol to a concentration of 20 wt% and stored in a refrigerator at ca. 4 C prior tofurther use.
2.3 Synthesis of poly(3-aminopropyl)silsesquioxane (PAPS)
PAPS was prepared from 3-aminopropyltriethoxysilane in the same way and obtained as a glasslike solid. PAPS was also diluted to a concentration of 20 wt% in ethanol and stored in a refrigerator.
2.4 Preparation of film coatings
A glass substrate was cleaned using detergent and then washed successively with distilled water,acetone, and 2-propanol. The 20 wt% ethanolic polymer solution prepared above was coated onto theglass substrate using an applicator. The film was heated at 60 C for 2 h, and then heated at 180 C for
0.5, 1, or 2 h in air to form a gel film.
23

For comparison, PVA films were prepared. PVA (2 g) was added to 20 mL of distilled water andstirred for 30 min, and then the obtained solution was coated onto a glass substrate using an applicator.
Finally, the PVA film was heated at 70 C for 3 h.
2.5 Characterization
1H nuclear magnetic resonance (NMR) measurements were performed using a Varian 400 MHz

spectrometer and 29Si NMR spectra were obtained using a Varian 500 MHz spectrometer. The samples
were dissolved in deuterium chloroform (CDCl3) and tetramethylsilane was used as an internal
standard. Fourier transform infrared (FTIR) spectra were recorded on a Shimadzu IR Affinity-1
spectrometer equipped with an attenuated total reflectance (ATR) unit. Transmittance measurements
were performed on a HITACHI U-2910 spectrophotometer. X-ray diffraction (XRD) analysis was
performed on a Rigaku Ultima IV diffractometer using Cu Kα radiation (λ= 1.54 Å) generated at 40
kV and 45 mA. Samples were scanned in the 2θ range 5°–40. Thermogravimetric analysis (TGA)
was performed using a SII EXSTAR TG-DTA6200 thermal analyzer at a heating rate of 10 C/min
under air flow at 100 mL/min. The contact angle was measured with KYOWA DM 300 contact angle
meter.
To measure water absorption, the films were placed in a humidity-controlled chamber at different
relative humidities (RHs) at 30 C for 1–2 h, and the weight changes were measured using a
microbalance. Water uptake was calculated using Equation (1):

𝑊𝑎𝑡𝑒𝑟 𝑢𝑝𝑡𝑎𝑘𝑒 (%) =𝑊95%𝑅𝐻 − 𝑊20%𝑅𝐻
× 100
𝑊20%𝑅𝐻(1)

where W20%RH is the weight of the film after exposure to 20% RH at 30 C for 1–2 h and W95%RH is
the weight of the film after exposure to 95% RH at 30 C for 1–2 h.
The scratch resistances, elastic moduli, and elastic part of indentation work (η) of the films were24measured using an Agilent Technologies Nano Indenter G200. Scratch resistance was measured by the
G-series ramp load scratch method with a cube corner diamond tip and calculated according toEquation (2) and (3). Elastic moduli and elastic part of indentation work (η) were measured with a
Berkovich diamond tip in accordance with ISO 14577-1 [10].

𝑆𝑐𝑟𝑎𝑡𝑐ℎ 𝑟𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 = 𝑙𝑜𝑔

𝑡𝑒𝑠𝑡 𝑙𝑜𝑎𝑑 (𝑁) × 10−92.5981 × (𝑝𝑙𝑎𝑠𝑡𝑖𝑐 𝑑𝑒𝑓𝑜𝑟𝑚𝑎𝑡𝑖𝑜𝑛 𝑑𝑒𝑝𝑡ℎ)2 (𝑚)2

𝑡𝑒𝑠𝑡 𝑙𝑜𝑎𝑑 (𝑁) × 10−9
= 𝑙𝑜𝑔
𝑐𝑜𝑛𝑡𝑎𝑐𝑡 𝑎𝑟𝑒𝑎 (𝑚2 )(2)

𝑃𝑙𝑎𝑠𝑡𝑖𝑐 𝑑𝑒𝑓𝑜𝑟𝑚𝑎𝑡𝑖𝑜𝑛 𝑑𝑒𝑝𝑡ℎ= (displacement depth into surface at postscratch)(3)− (displacement depth into surface at prescratch)

3. Results and discussion
3.1 Synthesis of amino-functionalized polysilsesquioxane
For the preparation of amino-functionalized polysilsesquioxanes, the author used 3aminopropyltriethoxysilane and 3-(2-aminoethylaminopropyl)triethoxysilane as the monomers. The
sol-gel reactions of 3-aminopropyltriethoxysilane and 3-(2-aminoethylaminopropyl)triethoxysilane
are shown in Scheme 1. Sol-gel reactions are typically accelerated under acidic or basic conditions,and hydrochloric acid is typically used as a catalyst [1, 2]. However, 3-aminopropyltriethoxysilane
and 3-(2-aminoethylaminopropyl)triethoxysilane have basic amino groups. Thus, the amino groups in
the monomer catalyze the hydrolysis and polycondensation reactions.

25

Scheme 1. Preparation of PAPS and PAEAPS by sol-gel reactions in ethanol.

First,

thehydrolysis

of

3-aminopropyltriethoxysilane

and

3-(2-

aminoethylaminopropyl)triethoxysilane was conducted at 0 C for 10 min and then at room
temperature for 10 min. Then, polycondensation was conducted under reflux for 5 h. PAPS andPAEAPS were obtained as a glass-like solid and a viscous liquid without gelation after the removal of
ethanol, respectively. PAEAPS exhibits good solubility in organic solvents such as THF, ethanol, andchloroform, whereas PAPS does not easily dissolve in organic solvents, taking several hours to fully
dissolve in ethanol.
The structures of PAPS and PAEAPS were investigated using 1H NMR and 29Si NMR analysis.
Figure 1 shows the 1H NMR spectra of PAPS and PAEAPS in CDCl3. For PAPS, the broad signals
observed at 0.51, 1.42, and 2.57 ppm are attributed to the propyl side chains. The amino group signal
overlaps with that for the propyl group at 1.42 ppm. The ethoxy group signals around 1.10 and 3.70
ppm are barely observed. Accordingly, the degree of hydrolysis of the ethoxy group was estimated to
be over 99%. Thus, the starting monomer is almost completely converted by hydrolysis, even though
no catalyst was added.

26

Figure 1. 1H NMR spectra of (a) PAPS and (b) PAEAPS in CDCl3.

Similarly, in the 1H NMR spectrum of PAEAPS, broad signals attributed to propyl groups areobserved at 0.58, 1.54, and 2.60 ppm, and ethyl group signals are observed at 2.60 and 2.77 ppm. The
two amino group signals overlap at 1.85 ppm. Again, the ethoxy group signals around at 1.20 and 3.80
ppm are almost completely absent following hydrolysis, and the estimated conversion is over 99%. As
expected, the amino groups in the starting monomer efficiently autocatalyze the sol-gel reaction.
Although the autocatalyzed sol-gel by nitrogen flow method was reported [11], the synthesized PAPS
and PAEAPS contained not ethoxy group, namely, the hydrolysis of ethoxy group efficiently
proceeded by autocatalyzed sol-gel reaction. In the nitrogen flow method, water was removed by theflow together with ethanol to make the fine control of the reaction possible. However, in the present
system, the staying water in the mixture accelerated further hydrolysis and polycondensation reaction.
The autocatalyzed sol-gel reaction is useful method to prepare polysilsesquioxane not containing
alkoxy group without adding catalyst. This is advantage of investigating the antifogging andmechanical property for avoiding the influence of alkoxy group because the remaining alkoxy groupis hydrophobic in nature and also sometimes affects the physical property such as thermal andmechanical property.
27

Figure 2 shows the 29Si NMR spectra of PAPS and PAEAPS in CDCl3. The 29Si NMR spectrumof PAPS features multiple sharp signals and small signals ranging from −65.7 to −70.8 ppm and −57.8
to −60.6 ppm, respectively. These signals are attributed to T3 and T2, where Tn denotes the siloxane
structural unit RSi(OSi)n(OR)3-n (n = 1–3, R = organic group). Although the author tried to estimate
the amount of silanol groups in PAPS by the 29Si NMR, it was difficult to detect the silanol groups
because their signals were considerably small, as shown in Figure 2. This result indicates that PAPS
is mainly composed of T3 structures. Thus, the results of 1H and 29Si NMR analyses for PAPS indicatethat the hydrolysis and polycondensation efficiently proceed under autocatalysis by the amino group,and that PAPS has highly network-like structure with a low content of ethoxy groups.

Figure 2. 29Si NMR spectra of (a) PAPS and (b) PAEAPS in CDCl3.

Similarly, the 29Si NMR spectrum of PAEAPS features multiple sharp signals in the range from−65.8 to −71.0 ppm attributed to T3 structures and small signals around at −58.4 ppm assigned to T2
structures. Thus, both PAPS and PAEAPS are mainly composed of T3 structures, demonstrating thatthe amino-functionalized polysilsesquioxanes adopt highly networked structures.
28

Kaneko et al. reported similar behavior for the acid-catalyzed sol-gel reactions of 3aminopropyltrimethoxysilane and 1-methyl-3-[3-(triethoxysilyl)propyl]imidazolium chloride, where
cage-type oligosilsesquioxanes were afforded as the main products [12-15]. Furthermore, the sol-gel
reaction of aminopropyltrimethoxysilane in a mixture of methanol and HCl at room temperature
affords a cage-like octa(3-aminoporpyl)silsesquioxane in the low yield of ca. 30% [16]. However, inthe case of PAPS and PAEAPS, polycondensation effectively proceeds by the catalytic effect of theamino group, and these sol-gel reactions not only form highly cross-linked structures, they may also
form partially condensed polysilsesquioxanes.
Regrettably, the molecular weights of PAPS and PAEAPS could not be measured by gel
permeation chromatography because the polymers adsorb onto the column resin through the polaramino group.
3.2 Preparation of polysilsesquioxane films
To assess the antifogging and mechanical properties of the polysilsesquioxane films, ethanolic
solutions of PAPS and PAEAPS were coated onto glass substrates and heated at 60 C for 2 h toremove the ethanol. Then, the films were heated at 180 C for 0.5, 1, or 2 h to promote gelation. To
investigate the structural changes in the PAEAPS film during heating, the reaction progress wasmonitored using ATR–FTIR measurements. Figure 3 shows the ATR–FTIR spectra of PAEAPS films
after drying at 60 C for 2 h and heating at 180 C for 0.5, 1, and 2 h. For the PAEAPS film dried at
60 C for 2 h, absorption peaks at 1093 and 1045 cm−1, which are attributed to the Si-O-Si bond, areobserved. Furthermore, a weak peak that corresponded to the silanol group appears around 900 cm−1.
As shown in Figure 3, the absorption peak around 900 cm−1 decreases with increasing heating time at
180 C. Furthermore, the absorption peak at 1045 cm−1 gradually increases in intensity with increasing
heating time and also shifts to 1020 cm−1. Thus, the Si-O-Si bond changes during heating at 180 C.
This indicates that PAEAPS forms a highly cross-linked network upon film formation. Indeed,
29

PAEAPS film did not peel off from glass substrate by tape testing and showed good adhesion probably
because of the formation of Si-O-Si bonds between PAEAPS and glass substrate. Accordingly, theobtained PAEAPS films are insoluble in ethanol and water. The obtained PAEAPS films are uniform,
transparent, and pinhole-free according to laser microscopy observation (Figure 4). Moreover, thePAEAPS film has a smooth surface and a root-mean-square (RMS) roughness of 68 nm, also
determined by laser microscopy (Figure 4). Similarly, PAPS also forms a highly cross-linked network
after heating at 180 C for 2 h. However, the PAPS films become turbid upon cooling to room
temperature, even though they are prepared by the same procedure as the PAEAPS films. The PAPS
film has a rougher surface and RMS roughness was 679 nm estimated by laser microscopy (Figure 4).
One possibility is that the surface roughness caused PAPS film turbid.

Figure 3. ATR–FTIR spectra of PAEAPS film after heating at 180 C.

30

Figure 4. Laser microscopy image of (a) the PAEAPS film after heating at 180 C for 1 h and (b) the
PAPS film after heating at 180 C for 1 h. Surface profile of (c) the PAEAPS film after heating at 180

C for 1 h and (d) the PAPS film after heating at 180 C for 1 h.

3.3 XRD analysis of PAPS and PAEAPS films
The PAEAPS film could have ladder-like or cage-like structures because its 29Si NMR spectrum
mainly shows multiple T3 peaks. Furthermore, the PAPS film may also comprise ladder-type or cagetype structures because it becomes a whitish solid upon curing. In other words, PAPS might form ahighly crystalline gel film. Therefore, XRD analysis of the PAPS and PAEAPS films was conducted31

to elucidate their structures. The XRD pattern of the PAPS film features distinct broad peaks at 8.08
and 21.13, as shown in Figure 5. Unlike the cage-type silsesquioxane amine salt [12-15], the PAPS
film is amorphous, as evidenced by the lack of sharp diffraction peaks in its XRD pattern. However,some distinct peaks can be observed, and the d-spacings were calculated to be 1.09 (d1) and 0.42 nm(d2). Thus, the XRD pattern of the PAPS film indicates the formation of ordered domains, namely,
ladder-like structures. According to previous reports, the d1-spacing corresponds to the intramolecular
chain-to-chain distance, i.e., the width of each double siloxane chain [17, 18]. Taken together, the XRD
pattern and 29Si NMR spectrum indicate that the PAPS film has not only amorphous structure but alsoa partial ladder-like structure because the broad peak at 8.08 corresponding to the d1-spacing isrelatively narrow and sharp and the T3 peak for the fully condensed silicon atom in the SiO3/2 unit ispredominant.

Figure 5. XRD patterns of (a) glass substrate, (b) PAPS film and (c) PAEAPS film after heating at 180
C for 1 h.
Similarly, the PAEAPS film shows distinct broad peaks at 6.24 and 21.38, as shown in Figure
5. Although PAEAPS is a viscous liquid, the obtained PAEAPS film shows diffraction peaks. The dspacings were calculated to be 1.41 (d1) and 0.42 nm (d2). Interestingly, the broad peak, corresponding
to d1-spacing, is presented at a lower angle compared with that of the PAPS film. This is due to the32different sizes of the substituent groups in the side chains of the PAPS and PAEAPS films. According
to a previous report, for octakis(dimethylsiloxy)octasilsesquioxanes having alkyl chains, thediffraction peak at 8 shifts to lower angles with increasing alkyl chain length [19]. In the case of the
PAEAPS film, the longer side chain leads to a longer intermolecular distance between neighboring
double siloxane chains.
3.4 Transparency of PAEAPS films
The transparencies and colors of antifogging materials are crucial parameters for their application
to optical lenses and vehicle windshields. However, PAPS films turn whitish and turbid upon coolingto room temperature. Therefore, only the optical properties of PAEAPS-coated glass were evaluated.
Accordingly, Figure 6 shows the UV-Vis transmission spectra of a glass substrate and PAEAPS films
heated at 180 C for 1–2 h. The glass substrate shows high transmittance in the wavelength range 400–
800 nm. Similarly, the PAEAPS film heated at 180 C for 1 h exhibits a transmittance of over 88% in
the wavelength range 400–800 nm, as shown in Figure 6. However, when the heating time is increased,
the transmittance of the PAEAPS film decreases. After heating at 180 C for 2 h, the transmittance of
the PAEAPS film at 400 nm decreases to 76% accompanied by a color change from colorless to lightyellow. This may be due to some denaturation such as oxidation of the amino groups in the side chains,even though no structural changes in the amino groups are indicated by the ATR–FTIR spectra of the
PAEAPS film.

33

Figure 6. UV-Vis spectra of a glass substrate and PAEAPS films prepared by heating at 180 C for 1
and 2 h.

3.5 Antifogging abilities of PAPS and PAEAPS films
To evaluate their antifogging properties, the water uptakes of PAEAPS, PAPS, and PVA films
were compared. Water uptake is defined by the weight difference at 20% RH and 95% RH, and it istypically used to evaluate the water absorption materials. It is enough to discuss the antifogging
property of films even though the water uptake might be not necessarily equal to antifogging property.
PAEAPS was coated onto a glass substrate and heated at 60 C for 2 h, and then at 180 C for 0.5–2
h. For measuring water uptake, the films with similar thickness of 8.4−14.9 μm were measured for
excluding the influence of film thickness. The author has also confirmed that the water uptake reachedequilibrium after 1−2 h after placing in a humidity-controlled chamber at different RHs at 30 °C. The
water uptake of the PAEAPS film increases with increasing RH in the range 20%–95%. For the
PAEAPS film prepared by heating at 180 C for 0.5 h, the water uptake at 95% RH was calculated to
be 52%. The water uptakes of the PAEAPS films decrease from 52% to 22% with increasing theheating time from 0.5 to 2 h, as shown in Table 1. As discussed above, PAEAPS forms a highly crosslinked network when the heating time is increased from 0.5 to 2 h. The formation of network Si-O-Si
34

bonds restricts the mobility of the polymer chains, decreasing water uptake. Furthermore, the PAEAPS
film before heating at 180 C contains hydrophilic silanol groups, which also absorb water, resulting
in a higher water uptake. As shown in Figure 3, the abundance of silanol groups decreases withincreasing heating time, and the water uptake of the PAEAPS films decreased from 52% to 22% at
95% RH. Conversely, the PAPS film prepared by heating at 180 C for 1 h exhibits a water uptake of
34%, which is lower than that of the PAEAPS film prepared under the same conditions, as shown in
Table 1. This is due to the difference in the hydrophilicities of the side chain in the polymer units,
where the PAEAPS film has two amino groups in each side chain. Although the author tried to estimate
the swelling ratio of PAEAPS film after exposure to 95% RH at 30 °C, the swelling change,
unfortunately, was not observed because the thickness of PAEAPS film was thin to observe theirchange. However, the wight change of PAEAPS film obviously indicated that PAEAPS film has theability to absorb the water.

Table 1. Antifogging and mechanical properties of PAEAPS and PAPS films
Curing time

WUa (%)

Scratch resistance

Elastic modulus
ηb (%)(h)(GPa)

PAEAPS film

0.5

52

2.3

1.2

54

PAEAPS film

1

42

2.8

2.0

58

PAEAPS film

2

22

3.2

3.7

61

PAPS film

1

34

-

1.4

22

PVA film

-

27

0.5

9.0

20

aWater uptake. bElastic part of indentation work.

The water uptake of the PAEAPS film prepared by heating at 180 C for 0.5 h is 1.9-times higher
than that of the corresponding PVA film (27%). For the PAEAPS films, the 3-(235aminoethyl)aminopropyl groups act as hydrophilic moieties and absorb water under high RH
conditions. The hydrophilic amino group is separated from the siloxane network by the alkyl chain
and the aminoethylaminopropyl group is flexible and easily rotates in the film state. Therefore,
PAEAPS films more effectively absorb water. In contrast, the water molecules cannot diffuse into the
PVA film because it has high crystallinity imparted by strong hydrogen-bonding interactions.
As mentioned above, PAEAPS films exhibit high water uptake. Thus, PAEAPS films have theability to prevent fog formation. To investigate the antifogging ability of PAEAPS, a bare glass
substrate and a PAEAPS-coated substrate were cooled to 4 C in a refrigerator and then exposed toambient air. The glass substrate immediately fogged in the air, while the PAEAPS-coated substrateretained its transparency. Furthermore, a glass substrate and a PAEAPS-coated substrate were exposed
to water vapor at 50 C for several seconds. Again, while the glass substrate quickly fogged, thePAEAPS film retained its transparency, as shown in Figure 7. This indicates that the PAEAPS film
quickly absorbs water and prevents the formation of fog. Interestingly, PAEAPS film exhibited
antifogging ability for several ten times when it was exposed to exhaled breath. In addition, PAEAPS
film has kept the antifogging ability for at least one month, showing the long-term stability.
To understand the mechanism of antifogging in PAEAPS film, water contact angle on the surface
was measured. Compared with superhydrophilic material, PAPS film and PAEAPS film exhibited highwater contact angles of 68° and 61°. However, PAEAPS film interestingly exhibited high water uptake
and ability to prevent fog formation. Therefore, the mechanism of antifogging in PAEAPS film wastotally different from superhydrophilic material. The water droplet contacted the surface of PAEAPS
film and then water molecules were gradually drawn by the amine moieties and permeated into
PAEAPS film. Thus, PAEAPS films exhibit high transparency even under humidified conditions andshow good antifogging ability.

36

Figure 7. Photographs of a PAEAPS film on the glass substrate (left) and a glass substrate (right)
exposed to water vapor.

3.6 Thermal stability of PAPS and PAEAPS films
Thermal stability is not necessarily an important property for antifogging materials, but it is ofinterest in the field of materials chemistry. Thus, the thermal stabilities of PAPS and PAEAPS films
were evaluated using TGA. To investigate the nature of antifogging materials exposed to atmosphericwater vapor, PAPS and PAEAPS films heated at 180 C for 2 h were left in ambient conditions forseveral days before measurement. As shown in Figure 8, TGA revealed a two-step weigh loss for
PAPS and PAEAPS films. The first weight loss (up to 180 C) is attributed to 8 and 14 wt% losses ofwater for PAPS and PAEAPS films, respectively. Interestingly, the loss of water weight for the
PAEAPS film is higher than that for the PAPS film. This is due to the difference in hydrophilicities ofthe films, i.e., the PAEAPS film has two amino groups in its side chains and tends to absorb and retain
water. Indeed, the water uptake of the PAEAPS film is higher than that of the PAPS film, as shown in
Table 1, and the weight loss is in good agreement with water uptake. The second weight loss starts ataround at 400 C and is assigned to the decomposition of the side chains (i.e., the aminopropyl groupand (2-aminoethyl)aminopropyl group). It should be noted that these hybrid-type antifogging materials

37exhibit considerable thermal stabilities compared with those of organic polymers.

Figure 8. TGA curves for PAPS and PAEAPS measured at a heating rate of 10 C/min under air.

3.7 Mechanical properties of PAPS and PAEAPS films
The scratch resistances of PAPS, PAEAPS, and PVA films were measured using a nanoindenter.
First, scratch profiles were obtained at a scan range of 1200 μm and a scratch speed of 50 μm/s by aramp loading of 0–20 mN on the surface of the film (Figure 9), and the scratch resistance wascalculated according to Eq. 2. PAEAPS films prepared by heating at 180 C for 0.5 h exhibit a scratch
resistance of 2.3. The scratch resistance of the PAEAPS films increases with increasing heating timeand reaches 3.2 after heating for 2 h. This increase in scratch resistance is attributed to the progress ofthe cross-linking reaction, as evidenced by the ATR–FTIR spectra of the PAEAPS films (Figure 3).
Although the scratch resistance of the PAPS film was expected to be similar to that of the PAEAPS
film, it was not measured because the film was not uniform. The PVA film exhibits a low scratch
resistance of 0.5. Thus, the scratch resistance of the PAEAPS film is 4–6 times higher than that of the38

PVA film. It has been reported that a Si-O-Si inorganic backbone structure imparts improved abrasion
resistance to a material [20]. Furthermore, it is reported that polyoctahedral silsesquioxanes exhibit
enhanced scratch resistance [21]. Therefore, the Si-O-Si network structure of the PAEAPS film
endows it with enhanced scratch resistance.

Figure 9. Scratch profile of (a) a PVA film and (b) a PAEAPS film prepared by heating at 180 C
for 1 h.

To improve the scratch resistance of antifogging materials such as PVA and polyacrylate, silica
nanoparticles were introduced into their film [22-24]. Indeed, the hardness of films increased withincreasing the amount of silica nanoparticles. In some cases, the trade-off relationship between theantifogging ability and the scratch resistance occurred by their strategy. Furthermore, the addition ofsilica nanoparticles decreases the transparency of antifogging film because of the aggregation of silica
nanoparticles. However, PAEAPS film exhibited the excellent antifogging ability and scratch
resistance without the additive because the PAEAPS films composed of the siloxane network andhydrophilic amino group. Furthermore, the decrease of transparency did not occur because there is notnecessarily to add the silica nanoparticles. These are good advantages for antifogging materials.
Recently, hybrid-type antifogging material also has been reported and this polyhedral oligomeric39

silsesquioxane-poly(quaternary ammonium-co-2-aminoethyl methacrylate hydrochloride) showed
excellent antifogging performance [25]. The content of polyhedral oligomeric silsesquioxane in thepolymer was considerably low and, unfortunately, their mechanical property of hybrid-type
antifogging material has not been mentioned. In contrast, the content of siloxane network in PAEAPS
film was considerably high, and it might enhance the scratch resistance.
To explore the high scratch resistance of the PAEAPS films, their mechanical properties werealso measured using the nanoindenter in accordance with ISO 14577-1. The elastic moduli and elastic
part of indentation work (η) of PAEAPS films heated at 180 C are shown in Table 1. The elastic
modulus increases with increasing heating time and reaches 3.7 GPa after heating at 180 C for 2 h.
This is because the cross-linking and formation of Si-O-Si bonds enhances the elastic modulus.
However, the elastic modulus of PVA is 9.0 GPa, which is higher than that of the PAEAPS film
prepared at 180 C for 2 h. It should be noted that the PAEAPS films exhibit high scratch resistanceseven though their elastic moduli are lower than that of the PVA film. The elastic part of indentation
work (η) of the PAEAPS and PVA films was calculated from the plastic deformation work and elastic
deformation work [10]. The η of the PAEAPS films was higher than that of the PVA film. The PVA
film exhibited a low elastic deformation work of 20%, indicating that the film showed low elastic
recovery. In contrast, the PAEAPS films exhibited a high elastic deformation work of 54−61%; in
particular, they easily recovered from deformation after nanoindentation, unlike the PVA film. Actually,
when the PAEAPS film surface was scratched in the range of 0−1200 μm using a ramp loading of
0−20 mN, the postscratch test showed an almost completely recovered surface from the rampedscratch test, as shown in Figure 9. On the other hand, the PVA scratch test showed slight recovery
from deformation during the lamp scratch test. These results indicate that a characteristic feature ofpolysiloxanes whereby flexible Si-O bonds help to recover from deformation and thus enhance scratch
resistance.
404. Conclusions
PAPS and PAEAPS were successfully prepared by sol-gel reactions autocatalyzed by the amine
moieties of the monomers. 1H and 29Si NMR analyses indicated that the hydrolysis andpolycondensation proceed efficiently, forming amine-functionalized polysilsesquioxanes with highly
cross-linked T3 structures. PAPS and PAEAPS showed good film-form ability, and the obtained films
were found to be uniform and pinhole-free. The XRD patterns of the PAPS and PAEAPS films
indicated the formation of ladder-like structures. The PAPS and PAEAPS films exhibit high water
uptakes of 34% and 42%, which are 1.2- and 1.5-times higher than that of the typical hydrophilicpolymer PVA. The optimal PAEAPS film showed the high scratch resistance of 3.2, which is 6–7times higher than that of a corresponding PVA film. Furthermore, a PAEAPS-coated glass substratedemonstrated excellent transparency and antifogging property. Thus, PAEAPS is a promising
candidate as an antifogging material that demonstrates both excellent antifogging property andappropriate scratch resistance simultaneously.

41

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43

Chapter 3: Enhancing Antifogging Property of Polysilsesquioxane Film
via an Amine Hydrochloride Salt
1. Introduction
As described in Chapter 2, the PAEAPS film absorbs water owing to hydrophilicity and flexibility of
3-(2-aminoethyl)aminopropyl group , and the siloxane network enhances their mechanical properties.
As a result, the PAEAPS film exhibited high water uptake and scratch resistance. Antifogging
materials based on PSQ may replace traditional antifogging materials. Therefore, further investigationof the structure and antifogging properties of PSQ films is required to develop high-performance
antifogging materials.
Previously, ionic units such as ammonium chloride and sulfobetaine that have stronger interaction
with water than polar functional groups were introduced into the polymer as hydrophilic groups [1, 2].
This is easily understood considering that ammonium salts are usually readily dissolved in water by
hydration

of

the

ionic

units.

For

example,thepolymer

containing

2-(methacryloyloxy)ethyltrimethylammonium chloride and sulfobetaine methacrylate exhibited highwater-absorbing capacity due to strong polymer-water interactions by strong hydrogen bonds [2]. In
Chapter 3, the author describes the preparation of amine salt-containing PSQ films, expecting that theamine hydrochloride salt could provide high water uptake. The influence of amine hydrochloride saltof PSQ on the antifogging properties and scratch resistance was investigated. In addition, the durabilityof PAEAPS and PAEAPS-Cl films under high humidity environments is also investigated to explore
the potential for practical application.

44

2. Experimental
2.1 Materials
PAEAPS was synthesized as described in Chapter 2. 3-(2-Aminoethylaminopropyl)triethoxysilane
and methyltriethoxysilane were purchased from Tokyo Chemical Industry Co. Ltd. (Tokyo, Japan) andused as received without further purification. Ethanol (superdehydrated) and 0.5 mol/L hydrochloric
acid (HCl) methanolic solution were purchased from FUJIFILM Wako Pure Chemical Co. Ltd. (Osaka,
Japan). Water was purified using a Millipore Milli-Q UV system and showed resistance and totalorganic carbon content values of 18.2 Mcm and <10 ppb, respectively. To clean the glass substrates
using an alkaline solution, KOH (50 g) was first dissolved in a mixture containing 2-propanol (600mL) and water (100 mL). Then, the glass substrates were immersed in this mixture for at least 15 h.
The cleaned glass substrates were washed with water twice and immersed in a 0.2 M HCl solution.
Finally, the cleaned glass substrates were rewashed with water and dried under an argon flow. The
water contact angle of the glass substrates was confirmed to be ~28°. The cleaned glass substrates
were immediately used for film preparation.
2.2 Measurements
1H nuclear magnetic resonance (NMR) measurements were performed on a Varian 400 MHz

spectrometer in deuterium chloroform (CDCl3) or deuterium oxide (D2O) using residual chloroform
or water as internal standards (7.26 ppm and 4.79 ppm) for chemical shift referencing. 13C and 29Si
solid-state NMR experiments were performed using a Varian System 600 spectrometer by magic-angle
spinning. For the 13C and 29Si solid-state NMR spectra, hexamethylbenzene and 3-(trimethylsilyl)propionic acid were used as external standards for chemical shift referencing. Fourier-transform
infrared (FTIR) spectroscopy was conducted in the transmittance mode on a Shimadzu IR Affinity-1
spectrometer. Size exclusion chromatography (SEC) was performed on a Shimadzu Prominence
HPLC System with triply connected Shodex OHpak SB-G/SB-805HQ/SB-804HQ columns calibrated
45

using poly(ethylene oxide). 0.2 mol/L sodium nitrate (NaNO3) solution was used as the eluent at aflow rate of 0.5 mL/min at 40 °C. Scanning electron microscopy (SEM) and energy-dispersive X-ray
spectroscopy (EDX) was performed using an EDX (GENESIS, EDAX) attached to a high-resolution
SEM (HITACHI S-5200). The PSQ film prepared on the Kapton film was coated with carbon by
sputtering to prevent charging. The scratch resistance and the elastic modulus of the PSQ film
containing the amine hydrochloride salt were measured by indentation and scratch tests using a Nano
Indenter G200 (the detailed procedure is provided in Chapter 2).
To measure the water uptake (WU) of the film, the 12.5-µm-film Kapton film was used as a substrate
to reduce the influence of the substrate weight error. The PSQ-OH film coated on the Kapton film
prepared using the aforementioned procedure was placed in a temperature- and humidity-controlledchamber, and the weight of the polymer film coated on the Kapton film was measured at 20% and
95% relative humidity (RH) for 2 h at 30 °C. The WU was calculated using Equation (1):

𝑊𝑈 (%) =𝑊95%𝑅𝐻 − 0.024 × 𝑊𝐾𝑎𝑝𝑡𝑜𝑛 − 𝑊20%𝑅𝐻
× 100,
𝑊20%𝑅𝐻(1)

where W20% RH and W95% RH denote the weight of the polymer film after exposure to 20% and 95%
relative humidity, respectively, at 30 °C for 2 h. WKapton denotes the weight of the Kapton film as thesubstrate and is corrected by taking into consideration the water absorbed by the Kapton film. The
Kapton film absorbed ~2.4 wt% water relative to its weight of the Kapton film under 95% relative
humidity at 30 °C.
2.3 Preparation of poly[3-(2-aminoethylamino)propyl-co-methyl]silsesquioxane (P(AEAP-coMe)S)P(AEAP-co-Me)S was synthesized by the reflux method described in Chapter 2. In a 100-mL
round-bottom flask equipped with a Dimroth condenser, 3-(2-aminoethylaminopropyl)triethoxysilane
46(5.289 g, 20.00 mmol), methyltriethoxysilane (1.783 g, 10.00 mmol), and ethanol (13.82 g, 300.0mmol) were mixed in an ice–water bath for 10 min. Water (1.081 g, 60.00 mmol) was slowly added,
and the reaction mixture was stirred at 0 °C for 10 min. Then, the mixture was stirred at room
temperature for 10 min and refluxed for 5 h. Finally, ethanol was removed under reduced pressure at
60 °C to obtain P(AEAP-co-Me)S as a viscous liquid. The obtained P(AEAP-co-Me)S was diluted
with ethanol to a concentration of 20 wt% and stored in a refrigerator at ca. 4 °C prior to further use.
1H NMR (400 MHz, CDCl , ppm): δ = 0.08 (1.1H, brs, SiCH ), 0.55 (2H, brs, SiCH ), 1.41–1.59
3
3
2(5.2H, brm, CH2, amino group, OCH2CH3), 2.54–2.74 (6H, brm, CH2 (adjacent to nitrogen atoms)),
3.76 (0.4H, m, OCH2CH3).
2.4 Preparation of poly[3-(2-aminoethylamino)propyl]silsesquioxane hydrochloride (PAEAPSCl)andpoly[3-(2-aminoethylamino)propyl-co-methyl]silsesquioxanehydrochloride(P(AEAP-co-Me)S-Cl) films by the immersion method
An ethanol solution of 20 wt% PAEAPS or P(AEAP-co-Me)S was coated on the glass substrateby an applicator with a clearance gap of 100 µm and heated at 60 °C and 180 °C for 2 h, respectively.
The obtained PAEAPS or P(AEAP-co-Me)S film on the glass substrate was immersed in 0.5 mol/L
HCl methanolic solution for 1 h and washed with methanol several times. Finally, the obtained
PAEAPS-Cl and P(AEAP-co-Me)S-Cl films on the glass substrate were dried at 60 °C for 30 min.
2.5 Synthesis of PAEAPS-Cl by the reaction of PAEAPS with HCl
In a 50-mL round-bottom flask was placed 551 mg (3.60 mmol) of PAEAPS as a viscous liquidand 18 mL of 0.5 mol/L HCl methanolic solution was slowly added. The white solid was gradually
precipitated, and the reaction mixture was stirred at room temperature for 1 h. Finally, the solvent wasremoved by an evaporator, and the white solid (809 mg, 99%) was dried at 100 °C for 2 h under avacuum.
1H NMR (400 MHz, D O, ppm): δ = 0.84 (2H, brs, CH ), 1.84 (2H, brs, CH ), 3.17 (2H, brs, CH ),
2
2
2
2

47

3.43–3.45 (4H, brm, CH2).
2.6 Preparation of the PAEAPS-Cl film by the coating method
PAEAPS-Cl was dissolved in water to obtain 20 wt% PAEAPS-Cl/water solution and coated on
the glass substrate by the applicator with a clearance gap of 100 µm. The wet film was heated at 60
and 180 °C for 2 h, respectively, to afford the PAEAPS-Cl film.

3. Results and discussion
3.1 Preparation of the PAEAPS-Cl film by the immersion method
For the preparation of PSQ films containing amine hydrochloride salts, two methods wereconducted as follows: (1) PAEAPS film was treated using a HCl methanolic solution to form the aminehydrochloride salt, and (2) PSQ having amine hydrochloride salt was synthesized, and coated on thesubstrate using the applicator, as shown in Scheme 1.
First, PAEAPS was coated on a silicon wafer and heated at 60 and 180 °C for 2 h, respectively.
The obtained PAEAPS film on silicon was immersed in 0.5 mol/L HCl methanolic solution for 1 h toconvert the amino group to the amine hydrochloride salt (Scheme 1). The chemical structures of the
PAEAPS and PAEAPS-Cl films were investigated by FTIR spectroscopy and 13C solid-state NMR. As
shown in Figure 1, the PAEAPS film showed distinct peaks at 1126 cm−1 and 1036 cm−1
corresponding to the siloxane bond, and small peaks corresponding to the amino group were observed
at 1666 cm−1 and 1603 cm−1 before HCl treatment. After immersion in 0.5 mol/L HCl methanolic
solution, a broad peak appeared in the range of 3500–2500 cm−1, and the small peaks corresponding
to the amino group slightly changed [3]. Then, in the 13C solid-state NMR spectrum of the PAEAPS
film (Figure 2), signals corresponding to the methylene group were observed at 9.2, 22.2, 40.5, and51.4 ppm. These signals shifted entirely to the upfield region after the conversion to the aminehydrochloride salt at 8.7, 19.1, 36.4, and 48.0 ppm. These results clearly supported that the amine48

group was converted to the amine hydrochloride salt upon immersion in 0.5 mol/L HCl methanolic
solution.

Scheme 1. Schematic illustrating the preparation of the PAEAPS-Cl film via the immersion method
and the coating method.

Figure 1. FTIR spectra of (a) PAEAPS film and (b) PAEAPS-Cl film prepared by immersion in 0.5
M HCl/MeOH solution for 1 h.

49

Figure 2. 13C solid-state NMR spectra of (a) PAEAPS film and (b) PAEAPS-Cl film prepared byimmersion in 0.5 mol/L HCl/MeOH solution for 1 h.

In addition, the introduction of chloride ions into the amino group was also confirmed by SEMEDX spectra before and after immersion in 0.5 mol/L HCl methanolic solution. In the PAEAPS film,
only the peaks attributed to carbon, oxygen, and silicon were observed at 0.25, 0.52, and 1.75 eV,
respectively. A new peak at 2.63 eV corresponding to the chloride atom appeared in the SEM-EDX
spectrum of the PAEAPS-Cl film after the formation of the amine hydrochloride salt (Figure 3). The
PAEAPS-Cl film maintained a smooth surface, and cracks and pinholes were not observed on thesurface and cross-sectional images of the PAEAPS-Cl film even after the formation of the amine
chloride salt (Figure 4). Furthermore, the elemental mapping image also showed that chloride atoms
were homogeneously distributed on the surface of the PAEAPS-Cl film, as shown in Figure 4.
Overall, FTIR, 13C solid-state NMR, and SEM-EDX results showed that the amine hydrochloride
salt was successfully formed by the neutralization of amino groups with HCl in the PAEAPS film.

50

Figure 3. Scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM-EDX) spectraof (a) poly[3-(2-aminoethylaminopropyl)]silsesquioxane (PAEAPS) film and (b) poly[3-(2aminoethylamino)propyl]silsesquioxane hydrochloride (PAEAPS-Cl) film prepared by immersion in
0.5 M HCl/methanol solution for 1 h.

Figure 4. SEM micrograph of (a) surface and (b) cross section of the PAEAPS-Cl film on the Kapton
film. (c) Elemental mapping image of chlorine atoms on the surface of the PAEAPS-Cl film.

3.2 Synthesis of PAEAPS-Cl and preparation of the PAEAPS-Cl film by the coating method
For the synthesis of PSQ having the amine hydrochloride salt, PAEAPS was reacted with HCl inmethanol (Scheme 1). As described in Chapter 2, PAEAPS shows high solubility in organic solvents,
including ethanol, chloroform, and acetone. The solubility of PSQ having the amine hydrochloride
51

salt was totally different, and the precipitant was obtained through the addition of an HCl methanolic
solution. The reaction mixture was stirred at room temperature for 1 h to attain the quantitative reaction.
PAEAPS-Cl was obtained as a white solid with a high yield (99%). The solubility of PAEAPS-Cl
drastically changed, and it did not dissolve in organic solvents, such as acetone, THF, chloroform,
methanol, and ethanol. Interestingly, PAEAPS-Cl dissolved in water, verifying that the amino group
in PAEAPS was converted to the amine hydrochloride salt. Then, the structure of PAEAPS-Cl was
confirmed using 1H NMR in D2O. All signals shifted downfield, and their signals were reasonable
based on the integration of the methylene proton (Figure 5). In Chapter 2, the molecular weight of
PAEAPS was not detected by SEC employing a polystyrene gel column in THF as an eluent because
PAEAPS was adsorbed on the column via the amino group. However, the ionization of the aminogroup prevented the adsorption on the column, and the molecular weight of PAEAPS-Cl was estimatedto be 5700 (weight-average) with a polydispersity index of 2.4 by SEC employing polyhydroxymethacrylate gel in a 0.2 mol/L NaNO3 solution.
Next, the PAEAPS-Cl solution in water was coated on a silicon wafer and heated at 60 °C and
180 °C for 2 h, respectively. In the FTIR spectrum of the PAEAPS-Cl film after heating at 60 °C for 2h, the peak of the siloxane bond was observed at 1132 cm−1 and 1042 cm−1, as shown in Figure 6.
After heating at 180 °C for 2 h, the intensity of the peak attributed to the siloxane bond at 1040 cm−1
increased (Figure 6), indicating that a network structure composed of siloxane bonds was formed bythermal curing, and the PAEAPS-Cl film was obtained by the coating process.

52

Figure 5. 1H nuclear magnetic resonance (NMR) spectra of (a) PAEAPS in CDCl3 and (b) PAEAPSCl in D2O.

Figure 6. FTIR spectra of the PAEAPS-Cl film prepared using the coating method (a) after heating at
60 °C for 2 h and (b) after heating at 180 °C for 2 h.

3.3 Synthesis of P(AEAP-co-Me)S and preparation of the P(AEAP-co-Me)S-Cl film by theimmersion method
To enhance the surface hardness of the PAEAPS film and investigate the influence of the number53

of amino groups on the antifogging property, P(AEAP-co-Me)S was also synthesized at a 3-(2aminoethylaminopropyl)triethoxysilane/methyltriethoxysilane molar ratio of 2/1 by hydrolysis andpolycondensation (Scheme 2). As described in Chapter 2, the amino groups in 3-(2aminoethylaminopropyl)triethoxysilane act as a catalyst for the hydrolysis and polycondensation
reaction.

Therefore,thehydrolysis

andpolycondensation

of

3-(2-

aminoethylaminopropyl)triethoxysilane and methyltriethoxysilane were conducted under the same
conditions without adding a catalyst for the preparation of PAEAPS. After the polycondensation
reaction, a viscous liquid was obtained upon the removal of the solvent. The structure of P(AEAP-coMe)S was investigated by 1H NMR. In the 1H NMR spectrum of P(AEAP-co-Me)S in CDCl3, thesignals attributed to the propyl group were observed at 0.55, 1.51, and 2.54 ppm, and part of the signal
was observed with the signal of the ethyl group in the ethoxy group at 2.54–2.74 ppm. Similarly, thesignals of two amino groups at 1.29 ppm overlapped with the signal of the propyl group. In PAEAPS,
over 99% of the ethoxy group was consumed because of amine autocatalyzation. In the preparation of
P(AEAP-co-Me)S, the hydrolysis and polycondensation reaction effectively proceeded, and theresidual ethoxy group was less than 5%. The composition of the aminoethylaminopropyl group andthe methyl group was estimated to be 2.7:1 based on the integration of methylene and methyl groups.
Although the number of methyl groups was slightly lower than the calculated value based on the feed
ratio, P(AEAP-co-Me)S with different contents of amino groups could be prepared bycopolymerization without gelation. P(AEAP-co-Me)S also showed good film-forming ability, and its
film containing the amine hydrochloride salt was also prepared similarly, as shown in Scheme 2.

54

Scheme 2. Synthesis of P(AEAP-co-Me)S via the hydrolysis and polycondensation of 3-(2aminoethylaminopropyl)triethoxysilane and triethoxymethylsilane and the preparation of theP(AEAP-co-Me)S-Cl film by the immersion method.

3.4 Antifogging and mechanical properties of the PAEAPS-Cl and P(AEAP-co-Me)S-Cl films
and its stability against water vapor
To investigate the influence of the amine hydrochloride salt on the antifogging and mechanicalproperties of the PAEAPS film, the WU of the PAEAPS-Cl film was measured and compared withthat of the PAEAPS film, along with the fog test conducted through exposure to water vapor. The
surface hardness of the PAEAPS-Cl film was also evaluated based on scratch resistance and elastic
modulus by the nanoindenter. The data are shown in Table 1. The PAEAPS film prepared by heatingat 180 °C for 2 h exhibits a WU of 22%. When the PAEAPS film on the glass substrate was exposed
to hot vapor at 40 °C at a distance of 2 cm, the PAEAPS film on the glass substrate became cloudy
within 9 s. On the other hand, the WU of the PAEAPS-Cl film increased up to 29% upon the
introduction of the amine hydrochloride salt structure. The PAEAPS-Cl film on the glass substrate55

maintained transparency for 8 s, which was almost similar to the PAEAPS film on the glass substrate.

Table 1. Antifogging properties and mechanical properties of PAEAPS, PAEAPS-Cl, and P(AEAPco-Me)S-Cl films
WUa (%)

fogging testb(s)scratchresistanceelastic
modulus(GPa)film state

PAEAPS

22

9

3.2

3.7

transparent

PAEAPS-Cl

29

8

4.3

3.4

transparent

P(AEAP-co-Me)S-Cl

17

7

3.7

2.6

transparent

aWater uptake. bFilm was exposed to hot vapor at 40°C at a distance of 2 cm, and an average of 3

measurements was presented.

Although the introduction of the amine hydrochloride salt apparently enhanced the WU, thedifference in the time of fog formation was not observed in the evaluation of the antifogging property
by the fog test. In the PAEAPS film, the amino group in the side chain absorbs water via hydrogenbonding and retains it in the film. In the case of the PAEAPS-Cl film, the absorption mechanism ofwater might be due to the hydrate around the chloride ion, similar to the polymer electrolyte membrane[4]. The hydrophilicity of the film totally increased by the introduction of the amine hydrochloride salt
structure, increasing the WU of PAEAPS-Cl. However, according to the fog test, the PAEAPS-Cl film
might slowly absorb water and retain water molecules around the salt structure. It is concluded thatthe absorption speed due to the hydration of water molecules is slower than that due to hydrogenbonding.
As shown in Table 1, the PAEAPS film prepared by heating at 180 °C for 2 h showed scratch
resistance and elastic modulus values of 3.2 and 3.7 GPa, respectively. Interestingly, the PAEAPS-Cl
56

film exhibited a high scratch resistance of 4.3. As discussed in Chapter 2, the scratch resistance of the
PAEAPS film is affected by the crosslinking density of the siloxane network. Indeed, the scratch
resistance of the PAEAPS film increased from 2.3 to 3.2 as the heating period increased from 0.5 h to
2 h. However, the crosslinking densities of the PAEAPS and PAEAPS-Cl films are similar because the
PAEAPS-Cl film, as well as the PAEAPS film, was also prepared by heating at 180 °C for 2 h. The
introduction of the amine hydrochloride salt into the PAEAPS film enhanced surface hardness. On theother hand, the elastic modulus of the PAEAPS-Cl film was similar to or slightly lower than that of
the PAEAPS film, indicating that the PAEAPS-Cl film tended to deform, compared with the PAEAPS
film, even though the amine hydrochloride salt structure increased the surface hardness. This may be
due to the presence of water molecules in the PAEAPS-Cl film. The PAEAPS-Cl film can retain watermolecules through hydration around the salt structure. Water molecules might have acted as aplasticizer, decreasing the elastic modulus of the PAEAPS-Cl film [5]. In addition, the high scratch
resistance of the PAEAPS-Cl film might be derived from the effect of water molecules as a plasticizer.
Importantly, both films exhibited high surface hardness compared with a (hydrophilic) poly(vinyl
alcohol) film.
The long-term stability of antifogging materials is an important factor from the viewpoint ofpractical applications. Thus, the PAEAPS and PAEAPS-Cl films were stored at 40 °C and 95% relative
humidity (RH) for 1 h for investigating film stability against water vapor. To investigate whether the
structural changes occur after exposure to water vapor at 40 °C and 95% RH for 1 h, the FTIR
measurements of the PAEAPS and PAEAPS-Cl films were conducted. In the FTIR spectrum of the
PAEAPS film, the peak corresponding to the amino group at 1643 cm−1 showed almost no change
after exposure to water vapor at 40 °C and 95% RH for 1 h, as shown in Figure 7 (a). However, thepeaks of the siloxane bond at 1132 cm−1 and 1038 cm−1 slightly changed. In the case of thepolymethylsilsesquioxane film, the peaks at 1120 cm−1 and 1030 cm−1 were assigned to the cage and57

network structures of siloxane bonds in the FTIR spectrum [6]. In the PAEAPS film, a subtle change
in the ratio of two peaks was observed before and after exposure to water vapor at 40 °C and 95% RH
for 1 h, indicating that the siloxane network structure attributed to the cage and network structure
might be changed. On the other hand, in the FTIR spectrum of the PAEAPS-Cl film, the change in the
structure of the PAEAPS-Cl film was not observed before and after exposure to water vapor at 40 °C
and 95% RH for 1 h, as shown in Figure 7 (b).

Figure 7. FTIR spectra of (a) PAEAPS film and (b) PAEAPS-Cl film before and after exposure tovapor at 40 °C and 95% for 1 h.

29Si

solid-state NMR afforded useful information on the structural changes of the siloxane

network in the PAEAPS film. In Figure 8 (a), the PAEAPS film mainly exhibited a strong peak at−66.9 ppm attributed to the T3 structure, along with a small T2 peak at −58.2 ppm. The peakcorresponding to the T3 structure decreased after exposure to water vapor at 40 °C and 95% RH for 1
h, and the peak intensities of the T3 and T2 structures were quite similar, indicating that the structure58

changed because of hydrolysis and the cleavage of the siloxane network. As described in Chapter 2,
PAEAPS was prepared by the autocatalyzed sol–gel reaction using the reflux method. In this reaction,
the amino group efficiently catalyzed the hydrolysis of the ethoxy group by water and thepolycondensation reaction of silanol in the polymer. Similarly, in the PAEAPS film, the amino groupacted as a base catalyst to facilitate hydrolysis. On the other hand, in the PAEAPS-Cl film, the T3
structure at −67.9 ppm was mainly observed even after exposure to water vapor at 40 °C, along withthe small T2 structure at −59.1 ppm in the 29Si solid-state NMR spectrum (Figure 8 (b)). It was
concluded that the introduction of the amine hydrochloride salt prevented the decomposition of thesiloxane network. As mentioned above, the siloxane network in the PAEAPS film was cleaved becauseof the basicity of amino groups. In the case of the PAEAPS-Cl film, the decomposition of the siloxane
network upon hydrolysis was prevented because the amine hydrochloride salt was almost neutral.
Therefore, the introduction of the amine hydrochloride salt structure increased the WU and prevented
the decomposition of the siloxane network. This means that the stability under high humidity was also
improved by the neutralization of the amino group.

Figure 8. 29Si solid-state NMR spectra of (a) PAEAPS film and (b) PAEAPS-Cl film before and after
exposure to vapor at 40 °C and 95% RH for 1 h.

59After exposure to water vapor at 40 °C and 95% RH for 1 h, the surface morphology of the
PAEAPS film was smooth, and no cracks were observed. However, the morphology of the PAEAPSCl film sometimes drastically changed, and cracks and dimples were observed by laser microscopy(data shown later). Interestingly, these morphological changes did not always occur, and the PAEAPSCl film sometimes showed a clear appearance after exposure at 40 °C and 95% RH for 1 h. Additionally,
the morphological change of the PAEAPS-Cl film prepared using the coating method was moresignificant than that prepared using the immersion method. When the PAEAPS-Cl film prepared using
the coating method was exposed to water vapor, a crack suddenly formed during the absorption ofwater.
The morphological change of the PAEAPS-Cl film might be due to the hydration aroundhydrophilic groups. In other words, the hydrated water induced the volume change in the PAEAPS-Cl
film, and their volume change was not maintained even though the siloxane network provided
excellent mechanical properties. Furthermore, the PAEAPS-Cl film prepared by the coating method
showed a more substantial morphological change than the PAEAPS-Cl film prepared using theimmersion method. Unfortunately, the WU of the PAEAPS-Cl film prepared using the coating method
could not be measured due to the strong morphological changes. In the PAEAPS-Cl film preparedusing the coating method, the siloxane network might not be formed efficiently because PAEAPS-Cl
contains a large side chain of the amine hydrochloride salt. As a result, the PAEAPS-Cl film preparedusing the coating method easily led to a morphological change. Overall, the introduction of an amine
salt structure enhanced the WU and surface hardness and prevented the hydrolysis of the siloxane
network. Unfortunately, cracks and dimples sometimes formed after exposure to water vapor. This isa significant disadvantage for the practical applications of the film.
P(AEAP-co-Me)S-Cl film was synthesized to enhance the surface hardness of the PAEAPS filmby the introduction of methyltrialkoxysilane, and their antifogging property and mechanical properties
60

were investigated. However, despite expectations, an interesting phenomenon was observed following
the copolymerization of methyltriethoxysilane. The P(AEAP-co-Me)S-Cl film exhibited a WU of 17%,
which was lower than those of the PAEAPS and PAEAPS-Cl films. When the P(AEAP-co-Me)S-Cl
film on the glass substrate was exposed to vapor at 40 °C at a distance of 2 cm, it turned cloudy after
7 s. This is reasonable because the number of amino groups decreased because of the copolymerizationof methyltriethoxysilane. However, the WU of the P(AEAP-co-Me)S-Cl film was sufficient to show
considerable antifogging performance. Contrary to expectations, the surface hardness and elastic
modulus of the P(AEAP-co-Me)S-Cl film were 3.7 and 2.6 GPa, respectively. As discussed in Chapter
2, the amino groups in 3-(2-aminoethylaminopropyl)triethoxysilane acted as the catalyst for thehydrolysis and polycondensation reaction, leading to a highly crosslinked network of siloxane bonds.
However, the number of amino groups decreased in the presence of methyltriethoxysilane. The
decrease in surface hardness might be due to the reduction in the network structure. On the other hand,the copolymerization of 3-(2-aminoethylaminopropyl)triethoxysilane and methyltriethoxysilane was
effective in improving stability under high humidity. In the FTIR spectra of the P(AEAP-co-Me)S-Cl
film before and after exposure to water vapor at 40 °C and 95% RH for 1 h, the structural change was
not observed, similar to the PAEAPS-Cl film (Figure 9). The P(AEAP-co-Me)S-Cl film maintained asmooth surface even after exposure to water vapor at 40 °C and 95% RH for 1 h, and cracks were notobserved. Figure 10 shows the laser microscopy image of the P(AEAP-co-Me)S-Cl film after
exposure to water vapor at 40 °C and 95% RH for 1 h, along with that of the treated PAEAPS-Cl film.
The surface of the PAEAPS-Cl film was considerably rough, and its root-mean-square (rms) roughness,
estimated by laser microscopy, was 773 nm after exposure to water vapor at 40 °C and 95% RH for 1
h. In contrast, the laser microscopy image of the P(AEAP-co-Me)S-Cl film showed a smooth surface
even after exposure to water vapor, and an rms roughness was determined to be 71 nm (Figure 10).
Therefore, in the P(AEAP-co-Me)S-Cl film, the volume change due to the hydration of water61

molecules was prevented by the decreased amount of the amine hydrochloride salt.

Figure 9. FTIR spectra of the P(AEAP-co-Me)S-Cl film before and after exposure to vapor at 40 °C
and 95% RH for 1 h.

(a)

(b)

(d)
20

20

15

15

Depth (m)

Depth (m)

(c)

10

5

0

10

5

0

50

100 150200

250 300

Distance (m)

0

0

50

100 150200

250 300

Distance (m)Figure 10. Laser microscopy images of (a) PAEAPS-Cl film and (b) P(AEAP-co-Me)S-Cl film after
exposure to vapor at 40 °C and 95% RH for 1 h. Surface profiles of (c) PAEAPS-Cl film and (d)P(AEAP-co-Me)S-Cl film after exposure to vapor at 40 °C and 95% RH for 1 h.
62

The transparency and color of antifogging materials are also important factors from the viewpointof practical applications. Figure 11 shows the UV-vis spectra of the PAEAPS, PAEAPS-Cl, andP(AEAP-co-Me)S-Cl films. The transmittance of the PAEAPS-Cl film at 400 nm was less than 85%,
which showed light-yellow. This may be due to oxidation of ammonium salts, similar to PAEAPS.

Figure 11. UV-vis spectra of PAEAPS, PAEAPS-Cl, and P(AEAP-co-Me)S-Cl films.

4. Conclusions
PAEAPS-Cl films containing amine hydrochloride salt were prepared by two methods: theimmersion method and the coating method. In the immersion method, the PAEAPS film on thesubstrate was immersed in 0.5 mol/L HCl methanolic solution. FTIR, 13C solid-state NMR, and SEMEDX results indicated that the amino group was converted to the amine hydrochloride salt upon
immersion in 0.5 mol/L HCl methanolic solution for 1 h. The PAEAPS-Cl film showed no cracks or
pinholes, and chloride atoms were homogeneously distributed on the surface of the PAEAPS-Cl film.
In the coating method, PAEAPS-Cl was synthesized by the treatment of PAEAPS with HCl for 1 h atroom temperature, and PAEAPS-Cl was obtained as a white solid with a yield of 99%. The obtained

63

PAEAPS-Cl did not dissolve in organic solvents but in water. The solubility of PAEAPS-Cl drasticallychanged following the introduction of the amine hydrochloride salt. The PAEAPS-Cl film was also
prepared by the coating method. The WU and surface hardness of the PAEAPS-Cl film prepared using
the immersion method were measured to investigate the influence of the amine hydrochloride salt on
the antifogging property and mechanical properties. The PAEAPS film showed a WU and scratch
resistance of 22% and 3.2, respectively. The introduction of the amine hydrochloride salt into the
PAEAPS film increased its antifogging property and surface hardness, and the WU and scratch
resistance of the PAEAPS-Cl film became 29% and 4.3. When the PAEAPS film was exposed to water
vapor at 40 °C and 95% RH for 1 h, the structural change of the siloxane network was observed
because of decomposition via the hydrolysis caused by the basicity of the amino group in the FTIR
and 29Si solid-state NMR results. On the other hand, as the amine hydrochloride salt structure wasalmost neutral, it prevented the cleavage of the siloxane network. However, the amine hydrochloride
salt sometimes induced the morphological change of the PAEAPS-Cl film owing to strong hydration,and cracks and dimples were observed after exposure to water vapor at 40 °C and 95% for 1 h, whereas
the P(AEAP-co-Me)S-Cl film exhibited a WU of 17%, which was lower than those of the PAEAPS
and PAEAPS-Cl films, but the cracks and dimples of the P(AEAP-co-Me)S-Cl films were notobserved even after exposure to water vapor at 40 °C and 95% RH for 1 h. The introduction of theamine hydrochloride salt structure did not decrease transparency. These findings are promising for
further design and development of antifogging materials with high-performance and long-term
stability.

645. References[1] C. Tao, S. Bai, X.H. Li, C. Li, L.X. Ren, Y.H. Zhao, X.Y. Yuan, Formation of zwitterionic coatings withan aqueous lubricating layer for antifogging/anti-icing applications, Progress in Organic Coatings 115(2018) 56-64.
[2] S. Bai, X.H. Li, R.C. Zhang, C. Li, K.Y. Zhu, P.C. Sun, Y.H. Zhao, L.X. Ren, X.Y. Yuan, Enhancing
antifogging/frost-resisting performances of amphiphilic coatings via cationic, zwitterionic or anionicpolyelectrolytes, Chemical Engineering Journal 357 (2019) 667-677.
[3] Y. Kaneko, N. Iyi, T. Matsumoto, K. Kitamura, Synthesis of rodlike polysiloxane with hexagonal phaseby sol-gel reaction of organotrialkoxysilane monomer containing two amino groups, Polymer 46(6) (2005)
1828-1833.
[4] J.R. Varcoe, P. Atanassov, D.R. Dekel, A.M. Herring, M.A. Hickner, P.A. Kohl, A.R. Kucernak, W.E.
Mustain, K. Nijmeijer, K. Scott, T.W. Xu, L. Zhuang, Anion-exchange membranes in electrochemicalenergy systems, Energy & Environmental Science 7(10) (2014) 3135-3191.
[5] T.T. Duy, S. Sawada, S. Hasegawa, Y. Katsumura, Y. Maekawa, Poly(ethylene-co-tetrafluoroethylene)(ETFE)-based graft-type polymer electrolyte membranes with different ion exchange capacities: Relative
humidity dependence for fuel cell applications, Journal of Membrane Science 447 (2013) 19-25.
[6] L.H. Lee, W.C. Chen, W.C. Liu, Structural control of oligomeric methyl silsesquioxane precursors andtheir thin-film properties, Journal of Polymer Science Part a-Polymer Chemistry 40(10) (2002) 1560-1571.

65

Chapter 4: Highly Transparent Antifogging Materials Based on
Polysilsesquioxane Containing a Hydroxy Group
1. Introduction
As described in Chapter 2 and 3, the PAEAPS film and PAEAPS-Cl film on a glass substrate showed
high transparency under humidified conditions and thus good antifogging properties. The amino andamine hydrochloride groups in the side chain effectively work to absorb water, and the siloxane
network enhances the scratch resistance. However, the transmittance of the PAEAPS film and
PAEAPS-Cl film decreases in the short-wavelength region and the film has a light yellow color
because of denaturation, such as the oxidation of the amino group and amine hydrochloride group in
the side chain. Therefore, a new design for PSQ-based antifogging materials is necessary; in particular,
the hydrophilic group must be changed to another hydrophilic group. For example, hydrophilicpolymers containing a hydroxy group have been widely studied as antifogging materials, althoughthese organic polymers exhibit low scratch resistance, and the hydroxy group is typically not prone todiscoloration. However, the preparation of PSQ film containing a hydroxy group is difficult becauseof the side reaction between silanol and hydroxy groups.
In Chapter 4, to develop a scratch-resistant, transparent, and colorless antifogging material, theauthor focused on 3-glycidyloxypropyltrimethoxysilane because the epoxy ring is hydrolyzed to forma hydrophilic diol group. The preparation of a PSQ film containing a high concentration of hydroxygroups while suppressing side reactions is described. The antifogging properties, mechanicalproperties, and transparency of the diol-containing film are discussed.

66

2. Experimental
2.1 Materials
Herein, 3-glycidyloxypropyltrimethoxysilane was purchased from Tokyo Chemical Industry Co.
Ltd. (Tokyo, Japan) and used as received without purification. Methanol (super dehydrated),
tetrahydrofuran (THF; super dehydrated), 2-propanol, 6 mol/L hydrochloric acid (HCl), 1 mol/L
sulfuric acid (H2SO4), and potassium hydroxide (KOH) were purchased from FUJIFILM Wako Pure
Chemical Co. Ltd. (Osaka, Japan) and used as received. The water used in the experiments was
purified using a Millipore Milli-Q UV system and showed a resistance and total organic carbon content
of 18.2 Mcm and <10 ppb, respectively. Glass substrates were cleaned in an alkaline solution. The
detailed procedure was described in Chapter 3. A 12.5-µm-thick Kapton film was purchased from AZ
ONE Corporation (Osaka, Japan).
2.2 Synthesisofpoly(glycidyloxypropyl)silsesquioxane(PGPS)byhydrolysis

andpolycondensation
PSQ with different molecular weights were synthesized according to the procedure described inprevious studies [1-3]. In a typical synthesis using a water/monomer molar ratio of 1.2, 3glycidyloxypropyltrimethoxysilane (4.727 g and 20.00 mmol) and methanol (6.408 g and 200.0 mmol)
were added to a 100-mL four-necked flask equipped with a mechanical stirrer and a nitrogen inlet andoutlet. The flask was placed in an ice-water bath, and the solution was stirred for 10 min with a rotation
speed of 150 rpm. A solution of 0.3646 g of 6 mol/L HCl and 0.1403 g of water was slowly added by
pipette under a nitrogen stream of 360 mL/min, and the reaction mixture was stirred at ice-water bathtemperature for 10 min and at room temperature for 10 min. Then, the reaction mixture was further
stirred at 80°C for 3 h with a rotation speed of 150 rpm under a nitrogen stream of 360 mL/min. PGPS
was obtained as a viscous liquid and dissolved in THF to a concentration of 50 wt%, and was stored
in a refrigerator until use.
67

The reaction ratios were estimated by the weight of the initial monomer and obtained polymer andthe molecular weight (Mw) of the monomer and polymer unit (RSiO1.5) by assuming that the hydrolysis
and polycondensation proceeded quantitatively according to Equation (1).

𝑅𝑒𝑎𝑐𝑡𝑖𝑜𝑛 𝑟𝑎𝑡𝑖𝑜 (%)
𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑚𝑜𝑛𝑜𝑚𝑒𝑟 − 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑 𝑝𝑜𝑙𝑦𝑚𝑒𝑟=
× 100(𝑀W 𝑜𝑓 𝑚𝑜𝑛𝑜𝑚𝑒𝑟 − 𝑀W 𝑜𝑓 𝑅𝑆𝑖𝑂1.5 ) × 𝑚𝑜𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑛𝑜𝑚𝑒𝑟(1)

2.3 Preparation of poly(3-(2,3-dihydroxypropoxypropyl)silsesquioxane) (PSQ-OH) film via
route AIn a 50-mL flask, 0.20 g of 50 wt% PGPS solution in THF was diluted with 0.80 g of THF andstirred at ice-water bath temperature for 10 min. To hydrolyze the epoxy group, 5 g of 1 mol/L HCl(aq) was added dropwise at ice-water bath temperature, and the resulting solution was stirred at room
temperature for 3 h. Finally, the reaction mixture was evaporated under reduced pressure and dried
under vacuum. PSQ-OH was obtained as a viscous liquid. For the film preparation, a 50 wt% PSQOH solution in THF was coated on a glass substrate using an applicator with a clearance gap of 50µm; then, the coated substrate was heated at 80 °C for 1 h and at 150 °C for 2 h.
2.4 Preparation of PSQ-OH film via route B
A 50 wt% PGPS solution in THF was coated on a glass substrate using an applicator with a clearance
gap of 50 µm, and the coated glass substrate was heated at 80 °C for 1 h and at 150 °C for 0.5–2 h.
Then, the obtained substrate was immersed in 0.5 mol/L H2SO4 for 1–15 h to hydrolyze the epoxy
group. After being washed several times with water, the polymer film on the glass substrate was driedat 60 °C for 1 h.

68

2.5 Measurements
1H and 29Si nuclear magnetic resonance (NMR) spectra were recorded on Varian 400-MHz and 500-

MHz spectrometers, respectively. Deuterium chloroform (CDCl3) was used as the solvent, andtetramethylsilane was used as an internal standard for chemical shift reference in the 1H and 29Si NMR
spectra. Solid-state 13C and 29Si NMR experiments were performed using a Varian 600-MHz
spectrometer by magic-angle spinning. Hexamethylbenzene and 3-(trimethylsilyl) propionic acid wereused as external standards for chemical shift reference in the 13C and 29Si NMR spectra, respectively.
Gel permeation chromatography was performed on a Shimadzu LC-20AD equipped with a CTO-20A
column oven and a RID-10A detector using triply connected TSKgel G6000H/G4000H/G2000H
columns that was calibrated using polystyrene standards. THF was used as the eluent at a flow rate of
1 mL/min (40 °C). For Fourier transform infrared (FTIR) spectroscopy, the polymer was coated ontoa silicon wafer and the FTIR spectrum of the polymer film on the silicon wafer was recorded in thetransmittance mode on a Shimadzu IRAffinity-1 spectrometer. The water uptake (WU) of the film
coated on the Kapton film was measured using a temperature- and humidity-controlled chamber. The
detailed procedure was described in Chapter 3.
Indentation and scratch tests were performed to evaluate the elastic modulus, scratch resistance,elastic part of indentation work (η), using a Nano Indenter G200. The detailed procedure is available
in Chapter 2.

3. Results and discussion
3.1 Synthesis of PGPS by hydrolysis and polycondensation
PGPS was synthesized by hydrolysis and polycondensation by the nitrogen flow method, as
illustrated in Scheme 1. The nitrogen flow method is useful for controlling the molecular weight of
PSQ by changing the water/monomer molar ratio, as reported in previous studies [1-5]. Therefore,
69

PGPS samples were synthesized by changing the water/monomer molar ratio to obtain a polymer withdifferent molecular weights, as presented in Table 1. With a water/monomer molar ratio of 1.2, theweight-average molecular weight (Mw) and polydispersity index (Mw/Mn) of PGPS were 5200 and 2.0,
respectively (Entry 1 in Table 1). The obtained PGPS was easily soluble in organic solvents, such asacetone, THF, and chloroform. The 1H NMR spectrum of PGPS with Mw of 5200 and Mw/Mn of 2.0 ispresented in Figure 1. Broad signals attributed to the propylene CH2-CH2-Si group were observed at
0.67 and 1.69 ppm, and signals attributed to the epoxy ring appeared at 2.60, 2.79, and 3.14 ppm. Twomethylene protons adjacent to an oxygen atom and methyl proton of the residual methoxy groupoverlapped at 3.37–3.73 ppm. Based on the integration of the methylene protons and methoxy protons,
the residual methoxy group against the methoxy group in the initial monomer was estimated to be
41%. The reaction ratio estimated based on the change in the weight of the film using Equation (1)was 63%, similar to the consumption of the methoxy group (59%) estimated using 1H NMR.

Scheme 1. Preparation of PGPS by hydrolysis and polycondensation.

70

When the water/monomer molar ratio was increased from 1.2 to 1.7, the molecular weight increased
from Mw = 5200 to 11000 (Entries 1–6 in Table 1). The reaction ratio also increased from 63% to 78%
with increasing the water/monomer molar ratio (Table 1). Finally, the formation of gel was observedwith the water/monomer molar ratio of 1.8 (Entry 7 in Table 1). In hydrolysis and polycondensationby the nitrogen flow method, a large amount of water facilitates efficient hydrolysis and moderate
polycondensation to form high-molecular-weight PGPS. Indeed, Mw linearly increased with increasingwater/monomer molar ratio (Figure 2), indicating that the molecular weight of PGPS could becontrolled by varying the amount of water. This trend is consistent with the hydrolysis andpolycondensation of bis(triethoxysilyl)ethane and triethoxymethylsilane by the nitrogen flow method[1, 3, 5].
Table 1. Results on the synthesis of PGPS
Entry

Water/monomer molar ratio

Mw

Mw/Mn

Reaction ratio (%)

1

1.2

5200

2.0

63

2

1.3

7300

2.2

70

3

1.4

11000

2.7

71

4

1.5

13000

3.2

73

5

1.6

22000

4.5

75

6

1.7

110000

19

78

7

1.8

Gel

71

Figure 1. 1H NMR spectrum of PGPS (Entry 1, Table 1) in CDCl3.

Figure 2. Influence of the water/monomer molar ratio on Mw of PGPS.

72

3.2 Preparation of PSQ-OH film via route A
Two routes were designed for the preparation of the PSQ-OH films (Figure 3). First, PGPS washydrolyzed under acidic or basic conditions to convert the epoxy groups to diol groups. When thehydrolysis of the epoxy group was performed in a mixture containing THF and water with nitric acidor HCl, the PGPS solution remained transparent for 3 h. The polymer was isolated via extraction withbrine to remove the acid; however, a gel was formed during extraction. In contrast, the hydrolysis of
the epoxy group in a mixture containing THF and ammonia solution produced gel during the reaction.
Therefore, HCl was used for the hydrolysis of the epoxy group by considering the removal of acid.
After the hydrolysis of the epoxy group in PGPS for 3 h, HCl and solvents were removed by a vacuum
pump at room temperature without extraction, and the obtained viscous liquid was dissolved in THF.
The polymer/THF solution was coated onto a silicon wafer for FTIR measurements and heated at
80 °C for 1 h and 150 °C for 2 h to obtain the PSQ-OH film (route A).

Route A

HCl (aq)

PGPS

Curingat 150 ºC

PSQ-OH

H2SO4 (aq)Curingat 150 ºC

PSQ-OH film

Route BPGPS film
Figure 3. Preparation of the PSQ-OH film via routes A and B.
73

To investigate the chemical structure, the PGPS film was also prepared on a silicon wafer by heating
the PGPS-coated wafer at 80 °C for 1 h and at 150 °C for 0.5 h (PGPS with Mw = 5200). For the PGPS
film, distinct absorption peaks at 1100 and 3450 cm−1, corresponding to the Si–O–Si bond and silanolgroup, respectively, were observed (Figure 4). A weak peak at ~900 cm−1, corresponding to the epoxy
ring, overlapped with the absorption peak of the silanol group. For the PSQ-OH film prepared via
route A, the absorption peak at ~3450 cm−1 increased by the formation of the diol group by hydrolysis.
However, it was difficult to quantify the formation of the diol group by FTIR measurement due to theoverlapping of the silanol and hydroxyl groups.

Figure 4. FTIR spectra of (a) PGPS film, (b) PSQ-OH film prepared via route A, and (c) PSQ-OH
film prepared via route B (immersion for 15 h).

To obtain further information, the hydrolyzed PGPS/THF solution was poured into apoly(tetrafluoroethylene-co-perfluoroalkyl vinyl ether) (PFA) vial, and a free-standing gel film of
PSQ-OH was prepared by heating at 80 °C for 1 h and 150 °C for 3 h for solid-state 13C NMR
74

spectroscopic measurements. Similarly, a free-standing gel film of PGPS was prepared by heating at
80 °C for 1 h and 150 °C for 3 h. The solid-state 13C NMR spectra before and after the hydrolysis of
PGPS are presented in Figure 5. In the spectrum of the PGPS film before hydrolysis, signals attributed
to the propylene group were observed at 7.5, 22.5, and 72.5 ppm. The peak at 70.9 ppm was attributed
to methylene carbon adjacent to an oxygen atom. Furthermore, peaks attributed to the epoxy ring wereobserved at 42.9 and 49.9 ppm. In the PSQ-OH film prepared via route A, the peaks attributed to theepoxy group at 42.9 and 49.9 ppm completely disappeared, and new peaks corresponding to the carbon
atom in the diol were observed at 62.8 and 69.3 ppm. It was observed that an unknown peak appearedat 45.6 ppm in the solid-state 13C NMR of PSQ-OH film prepared via route A. This may be due to aside reaction between the epoxy and silanol groups. For example, PSQ containing a hydroxy group
was prepared from hydroxymethyl(triethoxy)silane by hydrolysis and polycondensation [6]. In thisreaction, the condensation reaction of C–OH and Si–OH bonds occurred to form Si–O–C bonds athigh temperature. In the PSQ-OH film prepared via route A, a similar reaction may have occurred byheating the hydrolyzed film at 150 °C. If this peak was attributed to the Si–O–C bond formed by theside reaction of the epoxy and silanol groups, the Si–O–C bond should have been easily hydrolyzed.
However, the unknown peak did not disappear even after further hydrolysis of the PSQ-OH film.
However, FTIR and solid-state 13C NMR spectroscopy indicated that the epoxy group was fully
converted to a diol group by hydrolysis, which was sufficient to investigate the antifogging propertiesof the film.

75

Figure 5. Solid-state 13C NMR spectra of (a) PGPS film, (b) PSQ-OH film prepared via route A, (c)PSQ-OH film prepared via route B (after immersion for 7 h), and (d) PSQ-OH film prepared via route
B (after immersion for 15 h).

Finally, to prepare the PSQ-OH film on a glass substrate via route A, a 50 wt% PSQ-OH solution
in THF was coated onto an alkali-washed glass substrate and heated at 80 °C for 1 h and 150 °C for 2
h. The obtained PSQ-OH film was uniform and transparent.

3.3 Preparation of PSQ-OH film via route B
Next, a PSQ-OH film was prepared via route B (Figure 3). To prepare the PGPS film, a solution
containing PGPS with Mw = 5200 in THF was coated onto a glass substrate and heated at 80 °C for 1
h and 150 °C for 0.5–2 h. The obtained PGPS film was completely stiff and transparent without cracks.
When PGPS films were prepared using PGPS with Mw = 13000 and 22000 (water/monomer molar
ratio = 1.5 and 1.6), cracks were partially observed after heating at 150 °C for 3 h. This may be76

attributed to the high cross-linking ratio of the siloxane bond (Figure 6). The main signal at −66 ppm
attributed to the T3 structure was observed in the solid-state 29Si NMR of the PGPS films, where Tn
denotes the siloxane structural unit. The calculated cross-linking ratios of the PGPS films based on
T3/Ttotal ranged from 82% to 88%, which increased in the following order: water/monomer molar ratio= 1.2, 1.5, and 1.6. PGPS with a high molecular weight formed a cross-linked network, and theobtained film was too stiff, resulting in crack formation. Therefore, PGPS with an Mw of 5200
(water/monomer molar ratio = 1.2) was used for PSQ-OH film preparation.

Figure6.

29Si

solid-state

nuclearmagnetic

resonance(NMR)

spectraofpoly(glycidyloxypropyl)silsesquioxane (PGPS) films prepared by heating the polymer samples at
150 °C for 3 h. PGPS prepared by water/monomer molar ratio (r) = 1.2, 1.5, and 1.6 was used for film
preparation.

77

To investigate the reaction progress, the free-standing gel film of PGPS and the PGPS film on thesilicon wafer were immersed in a 0.5 mol/L H2SO4 aqueous solution for 1–15 h for the ring-opening
reaction of the epoxy group. As illustrated in Figure 4, a distinct broad peak corresponding to thehydroxy group was observed at ~3400 cm−1 in the IR spectrum, after immersion in the 0.5 mol/L
H2SO4 solution, indicating the formation of the diol group by hydrolysis. However, the conversion of
the epoxy group to the diol group could not be estimated using FTIR measurements because the peakof the hydroxy group overlapped with the absorption peak of the silanol group. However, solid-state
13C NMR spectroscopy successfully estimated the yield of the diol group formation. Figure 5 presents

the solid-state 13C NMR spectra of the PGPS and PSQ-OH films after immersion in 0.5 mol/L H2SO4(aq) for 7 and 15 h. The peaks at 42.9 and 49.9 ppm, corresponding to the epoxy ring carbons,decreased after immersion in 0.5 mol/L H2SO4 (aq) for 7 h. In addition to the reduction of the epoxy
ring signals, a new peak ascribed to one of the carbon atoms in the diol unit was observed at 63 ppm.
Another carbon atom in the diol overlapped with the methylene carbon adjacent to the ether group.
The peaks at 42.9 and 49.9 ppm completely disappeared after immersion in 0.5 mol/L H2SO4 (aq) for
15 h; in other words, the hydrolysis of the epoxy group quantitatively proceeded in this process. Unlike
the PSQ-OH film prepared via route A, no unidentified peak was observed in the solid-state 13C NMR
spectrum of the free-standing gel film of PSQ-OH. Overall, a PSQ-OH film containing a diol group
could be successfully prepared via route B (Figure 3). The PSQ-OH film was uniform and transparent,
similar to the PSQ-OH film prepared via route A. Furthermore, the PSQ-OH film did not peel off after
tape testing and exhibited good adhesion to the glass substrate owing to the formation of Si–O–Si
bonds, similar to the PAEAPS film.

78

3.4 Antifogging and mechanical properties of PSQ-OH film via routes A and B
To compare the antifogging and mechanical properties of the PSQ-OH films prepared via routes A
and B, the WU and scratch resistance were investigated; the results are presented in Table 2. The WUof the PSQ-OH film prepared via route A was only 5%, whereas that of the PSQ-OH film prepared
via route B was 5%–19%. As mentioned in the section Preparation of PSQ-OH film via route A, a side
reaction occurred during preparation, which may be responsible for the decrease in WU because theamount of hydrophilic materials in the film decreased by the reaction of C–OH and Si–OH that formeda Si–O–C bond. In the PSQ-OH film prepared via route B, the WU increased from 5% to 19% as theimmersion time was increased from 1 to 15 h. As shown in Figure 5, the epoxy ring was completelyhydrolyzed after immersion in 0.5 mol/L H2SO4 (aq) for 15 h. Therefore, the WU of the PSQ-OH film
depended on the number of diol groups. Furthermore, the WU of the PSQ-OH film decreased from
19% to 14% as the curing time increased from 0.5 to 2 h at 150 °C before immersion in 0.5 mol/L
H2SO4 (aq), likely because the enlargement of the PSQ-OH film by swelling with water was
suppressed by the enhanced cross-linking provided by the siloxane bond.

79

Table 2. Antifogging and mechanical properties of PSQ-OH film prepared via route A and route B
CuringFilm

Route

Elastic
Immersion

WU

time (h)

(%)

c

ηd

Scratchtime

modulusresistance

(h)

(%)
(GPa)

PSQ-OH film

Aa

2

PSQ-OH film

Bb

0.5

PSQ-OH film

Bb

PSQ-OH film
PSQ-OH film

5

1.6

0.2

94

1

5

3.6

0.9

70

0.5

9

12

2.7

1.5

72

Bb

0.5

15

19

2.7

1.1

76

Bb

2

15

14

3.5

1.9

61

22

3.2

3.7

61

27

0.5

9.0

20

PAEAPS film

2

PVA film

aPGPS was hydrolyzed in an aqueous HCl/THF solution to form a diol group; the hydrolyzed polymer

was coated on a glass substrate and heated at 150 °C for 2 h. bPGPS was coated on a glass substrate andimmersed in a 0.5 mol/L H2SO4 solution for the ring-opening reaction of the epoxy group. cWater uptake.
dElastic part of indentation work.

80

As described in Chapter 2, the PAEAPS film with an amino group in the side chain exhibited high
WU. The WU of the PSQ-OH film was lower than that of the PAEAPS film (Table 2) owing to thehydrophilicity of the side chain in the polymer. In other words, the amino groups in the side chain of
PAEAPS effectively absorbed more water than the hydroxy group in the side chain of PSQ-OH.
Similarly, the WU of the PSQ-OH film was lower than that of the PVA film. However, the PSQ-OH
film exhibited a WU of 5%–19%, which is sufficiently high for antifogging properties. Indeed, when
the PSQ-OH film with a WU of 19% and an average thickness of 5.3 µm coated on a glass substrate
was exposed to water vapor at 40 °C at a distance of 2 cm, it retained transparency for 13–16 s. In the
PSQ-OH film coated on the glass substrate, fogging was prevented by the absorption of water (Figure
7).

Figure 7. Photographs of the PSQ-OH film on a glass substrate (top) and a glass substrate without the
PSQ-OH film (bottom) exposed to water vapor.

The mechanical properties of the PSQ-OH film were evaluated using a nanoindenter, and the data
were compared with those of the PAEAPS and PVA films. The PSQ-OH film prepared via route B
exhibited a high scratch resistance of 2.7–3.6, similar to that of the PAEAPS film and 5–7 times higher
than that of the PVA film. However, the elastic moduli of the PSQ-OH films were 0.9–1.9 GPa, 5–10
81times lower than those of the PVA film. The high scratch resistance was attributed to the highly crosslinked siloxane network. Moreover, the flexible siloxane bond helped the film to recover fromdeformation, as described in Chapter 2. When the PSQ-OH film surface was scratched in the range of
0–1200 µm using a ramp loading of 0–20 mN, the post-scratch test revealed an almost completely
recovered surface from the ramped-scratch test (Figure 8). A similar phenomenon was observed in
the scratch profiles of PAEAPS film. Although the PVA film exhibited a high elastic modulus of 9
GPa, its scratch resistance was considerably low due to the lack of a restorative effect.
Furthermore, the PSQ-OH film exhibited a high elastic part of indentation work (η) of 67%–94%,
similar to that of the PAEAPS film. These results indicate that the siloxane network can recover fromdeformation in PSQ-OH films as well as in PAEAPS films.

Figure 8. Scratch profiles of PSQ-OH film prepared via route B (immersion for 15 h).

82

3.5 Surface morphology and transparency of PSQ-OH film prepared via route B
The surface morphology of the PSQ-OH film prepared via route B was investigated using laser
microscopy. The PSQ-OH film prepared by immersion in 0.5 mol/L H2SO4 (aq) for 15 h was uniform,
and pinholes and cracks were not observed (Figure 9). The root-mean-square (rms) roughness wasdetermined to be 54 nm using laser microscopy. The PSQ-OH film exhibited a smooth surface, similar
to that of the PAEAPS film (rms = 68 nm).

Figure 9. Poly(3-(2,3-dihydroxypropoxypropyl)silsesquioxane) (PSQ-OH) film prepared by route
B. (a) Laser microscopy image, and (b) surface profile of PSQ-OH film prepared by route B.

The transparency of antifogging materials is also important for practical applications. Figure 10
presents the UV–visible transmission spectra of a glass substrate, PAEAPS film, and PSQ-OH film
prepared via routes A and B. The glass substrate exhibited a high transmittance of 100% in the
wavelength range of 400–800 nm. The PAEAPS film prepared by heating at 180 °C for 1 h exhibiteda high transmittance of >88% in the wavelength range of 400–800 nm (Figure 10). However, thetransmittance of the PAEAPS film prepared by heating at 180 °C for 2 h decreased sharply to 76% at
400 nm. This indicates that the amino group in the side chain was unstable at high temperatures owing
to denaturation, such as oxidation. Alternatively, the PSQ-OH films prepared via routes A and B were83

highly transparent and colorless. In particular, the PSQ-OH film prepared via route B exhibited a hightransmittance of >98% in the wavelength range of 400–800 nm. The color of the PSQ-OH film did
not change even after several months. Unlike the amino group, the hydroxy group in the side chain of
the PSQ-OH film was stable at high temperatures because oxidation does not occur in ambient
atmosphere.

Figure 10. UV–visible spectra of a glass substrate, PSQ-OH film prepared via route A, PSQ-OH film
prepared via route B (where the PGPS film was prepared by heating at 150 °C for 0.5 or 2 h, and theobtained film was immersed in 0.5 mol/L sulfuric acid for 1, 9, and 15 h), and PAEAPS film.

4. Conclusions
PGPS was successfully synthesized by hydrolysis and polycondensation using the nitrogen flow
method. The molecular weight Mw of PGPS was controlled at 5200–110000 by changing thewater/monomer molar ratio from 1.2 to 1.7. PSQ-OH films containing a hydroxy group were prepared
via two routes. In route A, PGPS was hydrolyzed in an aqueous HCl/THF solution to form a diolgroup; the hydrolyzed polymer was coated on a glass substrate and heated at 150 °C for 2 h. The
84

obtained PSQ-OH film exhibited a low WU of 5% and a scratch resistance of 1.6 because of theformation of the Si–O–C bond via the side reaction between the silanol and hydroxy groups. In route
B, PGPS was coated on a glass substrate and immersed in a 0.5 mol/L H2SO4 solution for the ringopening reaction of the epoxy group. The hydrolysis of the epoxy group was confirmed using solidstate 13C NMR, and the epoxy group was completely hydrolyzed after immersion in the 0.5 mol/L
H2SO4 solution for 15 h. The WU of the PSQ-OH film prepared via route B increased from 5% to 19%
as the immersion time increased from 1 to 15 h and was higher than that of the PSQ-OH film prepared
via route A. The WU of the PSQ-OH film was 12%–19%, lower than those of the PAEAPS and PVA
films but sufficiently high to prevent fogging. Indeed, the PSQ-OH film on a glass substrate retainedtransparency when exposed to water vapor at 60 °C. The PSQ-OH film prepared via route B exhibiteda high scratch resistance of 2.7–3.6, similar to that of the PAEAPS film. Surprisingly, the scratch
resistance of the PSQ-OH film was 5–7 times higher than that of the PVA film. The PSQ-OH film
prepared via route B was uniform, and no pinholes and cracks were observed using laser microscopy.
The PSQ-OH film on a glass substrate was highly transparent and colorless and exhibited a hightransmittance of >90% in the wavelength range of 400–800 nm. Thus, this study presents a convenient
procedure for preparing a PSQ film containing a hydroxy group. The PSQ-OH film prepared via route
B is demonstrated to be an excellent antifogging material.

85

5. Reference[1] T. Ishimoto, S. Tsukada, S. Wakitani, K. Sato, D. Saito, Y. Nakanishi, S. Takase, T. Hamada, J. Ohshita,
H. Kai, Model-based research toward design of innovative materials: molecular weight prediction ofbridged polysilsesquioxanes, Rsc Advances 10(48) (2020) 28595-28602.
[2] S. Tsukada, Y. Nakanishi, T. Hamada, K. Okada, S. Mineoi, J. Ohshita, Ethylene-bridged
polysilsesquioxane/hollow silica particle hybrid film for thermal insulation material, Rsc Advances 11(40)(2021) 24968-24975.
[3] T. Hamada, T. Goto, S. Takase, K. Okada, A. Uedono, J. Ohshita, Structure-Thermal Property
Relationships of Polysilsesquioxanes for Thermal Insulation Materials, Acs Applied Polymer Materials 4(4)(2022) 2851-2859.
[4] N. Takamura, T. Gunji, H. Hatano, Y. Abe, Preparation and properties of polysilsesquioxanes:
Polysilsesquioxanes and flexible thin films by acid-catalyzed controlled hydrolytic polycondensation of
methyl- and vinyltrimethoxysilane, Journal of Polymer Science Part a-Polymer Chemistry 37(7) (1999)
1017-1026.
[5] T. Gunji, Y. Iizuka, K. Arimitsu, Y. Abe, Preparation and properties of alkoxy(methyl)silsesquioxanes
as coating agents, Journal of Polymer Science Part a-Polymer Chemistry 42(15) (2004) 3676-3684.
[6] K. Yamamoto, J. Ohshita, T. Mizumo, M. Kanezashi, T. Tsuru, Preparation of hydroxyl group containing
bridged organosilica membranes for water desalination, Separation and Purification Technology 156 (2015)396-402.

86

Chapter 5: Highly Durable Antifogging Polysilsesquioxane Film
Containing Tetraethylene Glycol Chains
1. Introduction
In Chapter 4, the PSQ-OH film exhibited a high scratch resistance, antifogging properties, andtransparency. For the practical applications of PSQ-OH, the author conducted a durability test on the
PSQ-OH film by keeping the film under humid and dry conditions repeatedly. From theaforementioned investigation, the PSQ-OH films revealed the following problems: (1) a decrease in
the water uptake (WU) and (2) the formation of cracks in the PSQ-OH film were observed during the
durability test. The author hypothesized that the decrease in WU and formation of cracks were due tothe polycondensation reaction between residual silanol groups in the PSQ-OH film during repeatedexposure to high and low humidity.
To address these problems, the author studied bridged PSQ prepared from organically bridged
trialkoxysilanes, [(RO)3Si–R–Si(OR)3] [1, 2], in which each silanol group is sterically separated by
the organic bridges, i.e., the polycondensation reaction of the residual silanol groups might beprevented by their space effect. In the present study, we employed hydrophilic ethylene glycol chain
as the spacer, expecting that its high hydrophilicity would not affect the antifogging property. The
preparation of high-performance antifogging films based on poly(ethylene glycol) (PEG) has beenreported, although their mechanical stability is low [3].
In Chapter 5, the effect of introducing ethylene glycol chains into a PSQ-OH film on the antifogging
property and durability of the diol-containing film is described. PSQs with diol groups andtetraethylene glycol units were prepared by a sol–gel reaction. Their antifogging property, mechanicalproperty, and durability are compared with those of the PSQ-OH film.

87

2. Experimental
2.1 Materials
3-Glycidyloxypropyltrimethoxysilane (GPTMS), tetraethylene glycol, allyl bromide, andtriethoxysilane were purchased from Tokyo Chemical Industry Co., Ltd (Tokyo, Japan) and used asreceived. In addition, tetraethyleneglycol diallylether (TEGDAE) and tetraethylene glycolbis(triethoxysilylpropyl)ether (BTESP-EG) were synthesized according to the previous study [4-6].
Super dehydrated methanol; tetrahydrofuran (THF); toluene; N,N-dimethylformamide (DMF); hexane(super dehydrated); 2-propanol; 6-mol/L hydrochloric acid (HCl); 1-mol/L sulfuric acid (H2SO4); andpotassium hydroxide (KOH) were purchased from Fujifilm Wako Pure Chemical Co., Ltd (Osaka,
Japan) and used as received. Sodium hydride (60% dispersion in mineral oil) and platinum(0)-1,3divinyl-1,1,3,3-tetramethyldisiloxane complex solution (Karstedt’s catalyst, in xylene, Pt ∼2%) werepurchased from Sigma-Aldrich. Water was purified using a Millipore Mill-Q UV system. The glass
substrates were washed using an alkaline solution according to Chapter 3. A Kapton film (thickness,
12.5 µm) was purchased from AZ One Corporation (Osaka, Japan).
2.2 Synthesis of tetraethyleneglycol diallylether (TEGDAE)
TEGDAE was synthesized according to previous studies [4, 5]. Sodium hydride (2.81 g, 70.4 mmolin mineral oil) and hexane (30 mL) were placed in a vacuum-dried 100-mL two-necked flask in anitrogen atmosphere. The mixture was stirred and allowed to stand, and the supernatant was removed
using a syringe. This process was repeated thrice to remove the oil of sodium hydride. A solution oftetraethylene glycol (2.51 g, 12.9 mmol) in DMF (25 mL) was slowly added to the flask, and the
mixture was stirred at room temperature for 20 min. Thereafter, allyl bromide (4.37 mL, 51.6 mmol)
was added dropwise, and the mixture was stirred overnight at room temperature. The reaction was
quenched by the addition of dilute hydrochloric acid (120 mL) in an ice bath. The product was
extracted with hexane (50 mL × 3), and the combined hexane solution was washed with water (50 mL
88

× 3), dried with anhydrous MgSO4, and the solvent was removed under reduced pressure. The productwas purified by silica gel column chromatography (eluent: ethyl acetate:hexane = 3:1) to yield
TEGDAE as a viscous liquid (75% yield).
1H NMR (400 MHz, CDCl , ppm): δ= 3.63 (16H, m), 4.02 (4H, m), 5.22 (4H, m), 5.91 (2H, m).
3

2.3 Synthesis of tetraethylene glycol bis(triethoxysilylpropyl) ether (BTESP-EG)
BTESP-EG was synthesized according to a reported procedure [6]. A mixture of TEGDAE (1.41 g,
5.13 mmol); triethoxysilane (2.11 g, 12.8 mmol); Karstedt’s catalyst (7.0 mg); and toluene (10 mL)
was placed in a 100-mL two-necked flask equipped with a nitrogen inlet and outlet. The reaction
mixture was stirred at 60 °C for 2 h, and the solvent was removed under reduced pressure to provide
BTESP-EG as a clear colorless oil.
1H NMR (400 MHz, CDCl , ppm): BTESP-EG: δ = 0.63 (4H, t, J = 8.4 Hz), 1.22 (18H, t, J = 7.0
3Hz), 1.70 (4H, quin, J = 7.0, 8.4 Hz), 3.43 (4H, t, J = 7.0 Hz), 3.59 (4H, m), 3.65 (14H, m), 3.82 (12Hq, J = 7.0 Hz); byproduct: δ = 1.56 (1.4H, m), 3.70 (1.1H, m), 3.87 (1.3H, m), 4.36 (0.4H, m), 4.77
(0.2H, m). 5.98 (0.2H, m), 6.25 (0.2H, m).
2.4 Synthesis of poly(glycidyloxypropyl-co-tetraethylene glycol)silsesquioxane (PSQ-Gly/EG)
GPTMS (0.709 g, 3.00 mmol); BTESP-EG (0.603 g, 1.00 mmol); and methanol (1.28 g, 40.0 mmol)
were added in a 100-mL flask equipped with a mechanical stirrer and nitrogen inlet and outlet. The
rotation speed and nitrogen flow rate were fixed at 150 rpm and 360 mL/min, respectively. The mixture
was stirred at ice-water bath temperature for 10 min. Afterward, 0.0407 g (5.50 mmol) of water and0.0730 g of 6 mol/L HCl were slowly added and successively stirred at ice-water bath temperature for10 min. The polycondensation reaction was conducted at room temperature for 5 h to yield PSQGly/EG. The obtained PSQ-Gly/EG was dissolved in THF to a 50 wt% solution and stored in arefrigerator until use. PSQ-Gly/EG with different feed ratios of GPTMS and BTESP-EG were also89

similarly prepared and denoted by PSQ-Glyx/EGy, where x and y indicate the feed ratios of GPTMS
and BTESP-EG.
2.5 Preparation of poly[3-(2,3-dihydroxypropoxypropyl)-co-tetraethylene glycol]silsesquioxane(PSQ-Diol/EG) film
PSQ-Diol/EG films were prepared according to the method described in Chapter 4. First, a 50-wt%
PSQ-Gly/EG–THF solution was coated onto a cleaned glass substrate using an applicator (clearance
gap of 50 μm) and heated at 80 °C and 150 °C for 1 and 0.5 h, respectively. The polymer-coated glass
substrate was immersed in 0.5-mol/L H2SO4 for 9–15 h at room temperature to convert the epoxy
group into a diol group. The obtained PSQ-Diol/EG film on the glass substrate was washed with water
several times and dried at 60 °C for 1 h.
2.6 Measurements
1H and 29Si nuclear magnetic resonance (NMR) measurements were performed using Varian 400

and 500 MHz spectrometers using deuterium chloroform (CDCl3) as a solvent and tetramethylsilane
as an internal standard. Gel permeation chromatography was performed using a Shimadzu LC-20AD
equipped with CTO-20A and RID-10A detectors and TSKgel G6000H/G4000H/G2000H columns at
40 °C with THF as an eluent at a flow rate of 1 mL/min. Fourier transform infrared (FT-IR)
spectroscopy was performed using a Shimadzu IRAffinity-1 spectrometer on a sample-coated siliconwafer in transmittance mode. To measure the water uptake (WU) of the PSQ-Diol/EG film, a PSQDiol/EG film was prepared on the Kapton film, and the PSQ-Diol/EG-coated Kapton film was placedin a temperature and relative humidity (RH)-controlled chamber and weighed after exposure to 20%
or 95% RH at 30 °C for 2 h. The detailed calculation for WU is described in Chapter 3. Indentationand scratch tests were performed to evaluate the elastic modulus and scratch resistance of the PSQDiol/EG film, respectively, using a Nano Indenter G200. The detailed procedure is available in
Chapter 2.
90

3. Results and discussion
3.1 Synthesis of PSQ-Gly/EG by hydrolysis/polycondensation reaction
The author investigated ethylene glycol chains as bridges for improving the durability of the PSQOH film. According to previous studies [4-6], BTESP-EG containing a hydrophilic tetraethylene
glycol unit was synthesized in two steps including the allylation of tetraethylene glycol andhydrosilylation reaction of the allylation product in a total yield of 65% (Scheme 1). After thehydrosilylation reaction, BTESP-EG was obtained as a clear colorless oil by the evaporation of solvent
and the unreactive triethoxysilane even without removal of Karstedt’s catalyst because the amount of
Karstedt’s catalyst was low for the hydrosilylation reaction. The chemical structure of BTESP-EG wasverified by its 1H NMR spectrum. Although small impurity peaks attributed to side reaction such as
the isomerization of allyl ether were observed, the main peaks were assigned to BTESP-EG bycomparison with the literature data [6].

H

Br

O
4

OH

HSi(OC2H5)3O
4

NaH, DMFO(C2H5O)3Si

4

Pt/toluene

O

O

Si(OC2H5)3

Scheme 1. Synthesis of tetraethylene glycol bis(triethoxysilylpropyl) ether (BTESP-EG).

91

PSQ-Gly/EG with different ratios of diols and tetraethylene glycol chains was synthesized fromGPTMS and BTESP-EG via hydrolysis/polycondensation using the nitrogen flow method (Scheme2) [7]. The results for PSQ-Gly/EG are shown in Table 1. When the polycondensation was conducted
at 50 °C–80 °C at a feed molar ratio of GPTMS and BTESP-EG = 3/1, the formation of gel wasobserved during the polycondensation reaction (Entries 1–2 in Table 1). The high network structure
was easily formed by the addition of BTESP-EG because of the bridged alkoxysilane containing six
alkoxy groups. Oppositely, the polycondensation reaction at room temperature afforded a highly
viscous product that was soluble in typical organic solvents, such as THF and chloroform after 5 h(entry 3 in Table 1). The obtained PSQ-Gly3/EG1 possessed a low weight-average molecular weight(Mw) of 800 and polydispersity index (Mw/Mn) of 1.7 (entry 3 in Table 1). The 1H NMR spectrum of
PSQ-Gly3/EG1 is shown in Figure 1. The broad signals at 0.73 and 1.8 ppm were attributed topropylene units at α- and β-positions to Si, respectively. Signals attributed to other protons of theglycidyloxypropyl unit were observed in the same regions as those of the PGPS, as described in
Chapter 4. The signal attributed to the methylene adjacent to the oxygen of tetraethylene glycol wasobserved at 3.7 ppm. Peaks of residual ethoxy groups were observed at 1.2 and 3.8 ppm. Based on the
integration of the methylene proton of Si-CH2 and the ethoxy proton, 85% of the ethoxy groups were
calculated to be consumed by the hydrolysis/polycondensation reaction. The 29Si NMR spectrum of
PSQ-Gly3/EG1 is shown in Figure 2, along with those of GPTMS, PGPS, and BTESP-EG. Four kindsof peaks attributed to T0, T1, T2, and T3 were observed in ranges of –40.4 to –42.8 ppm, –49.0 to –51.4
ppm, –57.4 to –59.8 ppm, and –66.0 to –69.0 ppm, respectively, in the PSQ-Gly3/EG1 spectrum.
BTESP-EG exhibited a sharp signal at –45 ppm, which completely disappeared after thepolycondensation reaction, as shown in 29Si NMR spectrum of PSQ-Gly3/EG1. Contrarily, the T0
signal of GPTMS remained or was slightly shifted. In the 29Si NMR spectra of PSQ-Gly3/EG1 and
PGPS, the positions of the peaks derived from the T1 and T2 structures were slightly shifted. Overall,92

the tetraethylene glycol chain was introduced into PSQ-OH, and PSQ-Gly3/EG1 was successfully
synthesized by the copolymerization of GPTMS and BTESP-EG.

OMe
MeO Si OMe+O(C2H5O)3Si

H2O, HCl
MeOH

O

GPTMS

n

4

Si(OC2H5)3

BTESP-EG

O

OR
Si O

O

OR'
Si
OR'

O

O

4

OR'
Si O
OR'

Si
R, R' =
m

H
Me ,

Et

O
O
PSQ-Gly/EG

Scheme 2. Preparation of poly(glycidyloxypropyl-co-tetraethylene glycol)silsesquioxane (PSQGly/EG) using the sol–gel method.

93

Table 1. Results of the synthesis of poly(glycidyloxypropyl-co-tetraethylene glycol)silsesquioxane(PSQ-Gly/EG)
Feed molar ratio of
Entry

TemperatureTime

Copolymer
GPTMS:BTESP-EG:H2O

(°C)

(h)

Mw

Mw/Mn

1

PSQ-Gly3/EG1

3.0:1.0:5.5

80

3

2

PSQ-Gly3/EG1

3.0:1.0:5.5

50

3

3

PSQ-Gly3/EG1

3.0:1.0:5.5

r.t.

5

800

1.7

4

PSQ-Gly1/EG1

2.0:2.0:5.0

r.t.

5

700

1.6

5

PSQ-Gly1/EG3

1.0:3.0:4.5

r.t.

5

680

1.5

Figure 1. The 1H NMR spectrum of poly(glycidyloxypropyl-co-tetraethylene glycol)silsesquioxane(PSQ-Gly3/EG1) in CDCl3.
94Figure 2. The 29Si NMR spectra of (a) poly(glycidyloxypropyl)silsesquioxane (PGPS), (b)tetraethylene

glycolbis(triethoxysilylpropyl)ether(BTESP-EG),

(c)

3-

glycidyloxypropyltrimethoxysilane (GPTMS), and (d) poly(glycidyloxypropyl-co-tetraethylene
glycol)silsesquioxane (PSQ-Gly3/EG1) in CDCl3.

Similarly, PSQ-Gly/EG with different feed ratios of GPTMS and BTESP-EG were prepared with
their Mw and Mw/Mn ranged from 680–700 and 1.5–1.6, respectively (Entries 4–5 in Table 1).
Unfortunately, the storage stability of PSQ-Gly/EG was extremely low, and the Mw of PSQ-Gly/EG
increased from 800 to 11000 after 8 days even under storage in a refrigerator. Therefore, to ensure therepeatability of the film preparation, the PSQ-Gly/EG films were prepared within one day after thesynthesis of PSQ-Gly/EG. No significant changes of the polymer molecular weights and the NMR
spectra were found within one day.

3.2 Preparation of PSQ-Diol/EG film
The ring-opening reaction of epoxy groups in the PSQ-Gly/EG film prepared on the glass substrate
was conducted by immersion in sulfuric acid to prepare the PSQ-Diol/EG film (Scheme 3). To
95

investigate the progress of the ring-opening reaction of the epoxy groups, a THF solution containing
PSQ-Gly1/EG1 containing the same amount of epoxy group and tetraethylene glycol chain was coatedonto the silicon wafer and heated at 80 °C and 150 °C for 1 and 0.5 h, respectively. Thereafter, theresultant PSQ-Gly1/EG1 films on the silicon wafer were immersed in a 0.5-mol/L H2SO4 aqueous
solution for 9 and 15 h. The FT-IR spectrum of the PSQ-Gly1/EG1 film exhibited a peak around 1100
cm–1 corresponding to the Si–O–Si bonding (Figure 3). When the film was immersed in H2SO4 (aq)for 9 h, the peak intensity of the hydroxyl groups around 3000–3600 cm–1 increased. It took 15 h for
the PSQ-OH film to wholly convert the epoxy group into a diol group under the same conditions.
However, for PSQ-Gly1/EG1, no evident changes in the FT-IR spectrum were observed after further
immersion of the film for an additional 6 h (Figure 3(c)). To obtain additional information for the
ring-opening reaction, the surface property was investigated with respect to the water contact angle,
which drastically changed prior to and after the ring-opening reaction of the epoxy group. The PSQGly1/EG1 pristine film exhibited a water contact angle of 71°. After immersion for 15 h, the watercontact angle decreased to 59°. This means that the epoxy groups were wholly converted into diolgroups after immersion in H2SO4 (aq) for 15 h. Furthermore, the PSQ-Diol1/EG1 films prepared byimmersion in H2SO4 (aq) for 9 and 15 h exhibited similar WU (vide infra). The surface of the PSQDiol1/EG1 film prepared on the glass substrate was smooth and free of pinholes, and the root-meansquare (rms) was determined to be 0.15 μm by laser microscopy even after immersion in H2SO4 (aq),indicating the formation of a crack-free, transparent, and tack-free PSQ-Diol /EG film using theimmersion method.

96

Curing

PSQ-Gly/EG

Scheme3.

Preparationof

H2SO4 (aq)

glass

glass

PSQ-Gly/EG film

PSQ-Diol/EG film

thepoly[3-(2,3-dihydroxypropoxypropyl)-co-tetraethylene

glycol]silsesquioxane (PSQ-Diol/EG) film.

Figure 3. FT-IR spectra of the (a) poly(glycidyloxypropyl-co-tetraethylene glycol)silsesquioxane(PSQ-Gly1/EG1); (b) poly[3-(2,3-dihydroxypropoxypropyl)-co-tetraethylene glycol]silsesquioxane(PSQ-Diol1/EG1) (immersion for 9 h); and (c) PSQ-Diol1/EG1 films (immersion for 15 h).

97

3.3 Antifogging and mechanical property of PSQ-Diol/EG film
To investigate the antifogging and mechanical properties of the PSQ-Diol/EG films, the WU,
scratch resistance, and elastic modulus were evaluated and are summarized in Table 2. The WU of
the PSQ-Diol/EG films was practically independent of the amount of tetraethylene glycol units,
ranging from 15% to 19%, and these values were similar to those of the PSQ-OH films (WU of 12–19%). Similar water contact angles were observed for the PSQ-OH and PSQ-Diol1/EG1 films (63° and
59°, respectively) immersed in a 0.5-mol/L H2SO4 aqueous solution for 15 h, despite the decrease in
the number of hydroxyl groups in the PSQ-Diol/EG film, compared with the PSQ-OH film. This
indicated that the tetraethylene glycol chains contributed to retaining the hydrophilicity of the film.
The contact angle of the PGPS and PSQ-Gly/EG films without hydroxyl groups were 82° and 71°,
respectively. The smaller contact angle of the PSQ-Gly/EG film indicated that the tetraethylene glycol
chains endowed the film with hydrophilicity. A glass substrate and a PSQ-Diol1/EG1 film on a glass
substrate prepared by immersion in a 0.5-mol/L H2SO4 aqueous solution for 15 h were exposed towater vapor at 50 °C for several seconds. The glass substrate rapidly fogged, and the PSQ-Diol1/EG1
film on the glass substrate maintained its transparency (Figure 4). This indicated that the PSQDiol1/EG1 film exhibited antifogging properties.

98

Table 2. Antifogging and mechanical properties of the poly[3-(2,3-dihydroxypropoxypropyl)-cotetraethylene glycol]silsesquioxane (PSQ-Diol/EG) film
Immersion time (h)WU (%)

Scratch resistance

Elastic modulus (GPa)PSQ-OH

9

12

2.7

1.5

PSQ-OH

15

19

2.7

1.1

PSQ-Diol3/EG1

15

15

3.3

1.2

PSQ-Diol1/EG1

9

19

3.5

1.2

PSQ-Diol1/EG1

15

18

2.4

1.1

PSQ-Diol1/EG3

15

16

3.2

1.2

27

0.5

9.0

PVA

Bare glass

Coated glass

Figure 4. Photograph of the glass substrate (upper) and poly[3-(2,3-dihydroxypropoxypropyl)-cotetraethylene glycol]silsesquioxane (PSQ-Diol1/EG1) film on the glass substrate (immersion for 15 h)(lower) exposed to water steam.

99

The PSQ-OH film exhibited a high scratch resistance of 2.7–3.6, which was 5–7 times higher thanthat of the PVA film. The scratch resistance of PSQ-Diol/EG films ranged from 2.4 to 3.5, comparable
to that of PSQ-OH. In the scratch profile of the PSQ-Diol1/EG1 films prepared on glass substrates by
the nanoindenter scratch test (Figure 5), the profile during scratching (ramped scratch) deformed toapproximately 4500 nm in displacement into the surface. Oppositely, the postscratch profile wasnearly identical to the prescratch profile because of the recovery from the deformation during
scratching. The high elasticity recovery of the flexible siloxane bond appeared to assist the recovery
from deformation, as described in Chapter 2. These results indicated that the tetraethylene glycol
chains did not decrease the scratch resistance, and the PSQ-Diol/EG films were highly scratchresistant.

Figure5.

Scratchprofileofthepoly[3-(2,3-dihydroxypropoxypropyl)-co-tetraethylene

glycol]silsesquioxane (PSQ-Diol1/EG1) film (immersion for 9 h).

100

3.4 Durability of PSQ-Diol/EG film on humidity and temperature change
If an automobile windshield is coated with an antifogging film, the coated film prevents fogging byabsorbing water droplets that condense on the windshield surface. However, fogging occurs when theantifogging film is saturated with water (over WU), i.e., the water droplets that cannot be absorbed by
the antifogging film form on the film surface. Therefore, the absorbed water in the film must be driedby a heater, such as a defogger system, before reaching saturated water absorption. In addition,
considering the atmospheric conditions in said automobile, antifogging films must maintain theirantifogging ability, surface smoothness, and transparency even after repeated moisture absorption anddesorption. Therefore, after repeated exposure to humid and dry air, the change in WU was monitored
to investigate the durability of the antifogging property, surface smoothness, and transparency of the
PSQ films through the repeated absorption and desorption of water vapor.
(1) Effect of tetraethylene glycol chain on the antifogging property through repeated testing bychanging the humidity
The author performed repeated testing of moisture absorption and desorption on the PSQ-Diol1/EG1
and PSQ-OH films. The change in WU was monitored during five repeated cycles at 20% and 95%
RH at 30 °C (Figure 6). The WU of the PSQ-OH film at 95% RH gradually decreased from 16% to
14% after the fifth cycle. Conversely, the WU of the PSQ-Diol1/EG1 film did not exhibit a changeeven after the fifth cycle. In Chapter 2, the WU of the PAEAPS films decreased from 52% to 22%
with an increase in the heating time at 180 °C from 0.5 to 2 h. The decrease in WU was due to theformation of a highly crosslinked siloxane network when the heating time was increased from 0.5 to
2 h. Similarly, the author considered that the decrease in WU of the PSQ-OH film after repeatedexposure to high and low humidity was due to the formation of a crosslinked siloxane network by thepolycondensation reaction of the residual silanol groups. In preparation method, silanol groups wereformed in the PSQ-OH and PSQ-Diol/EG films by the hydrolysis reaction of residual alkoxy groups101

in the films during the ring-opening reaction of the epoxy group. In the course of desorption testing,the remaining silanol groups in the film reacted with each other to form a siloxane bond by thepolycondensation reaction. Thus, the decrease in the WU of the PSQ-OH film was observed after
repeated absorption and desorption cycles. Contrarily, the PSQ-Diol1/EG1 film contained tetraethylene
glycol chains between the silicon atoms, which provided space between the siloxane backbone andthe distance between the silanol groups to prevent a further polycondensation reaction of the silanolgroups.

Figure 6. Water uptake (WU) of the (a) poly[3-(2,3-dihydroxypropoxypropyl)]silsesquioxane (PSQOH) film prepared by immersion in 0.5-mol/L sulfuric acid for 15 h (black circles). (b) Poly[3-(2,3dihydroxypropoxypropyl)-co-tetraethylene glycol]silsesquioxane (PSQ-Diol1/EG1) film prepared byimmersion in 0.5-mol/L sulfuric acid for 9 h (light blue circles) and 15 h (blue circles) after placing
the films at a relative humidity (RH) of 20% (D) and 95% (W), respectively, for 2 h at 30 °C.

(2) Effect of tetraethylene glycol chain on the surface smoothness through repeated testing bychanging humidity and temperature

102

The PSQ-OH and PSQ-Diol1/EG1 films were exposed to water vapor at 50 °C at 95% RH for 1–7
days to investigate their durability regarding surface smoothness. Their appearance was observed
using a laser microscope under atmospheric conditions. For the PSQ-OH film, the formation of cracks
was partially observed, and a part of the PSQ-OH film was peeled off from the glass substrate after 1
day at 50 °C and 95% RH. Overall, the formation of cracks and the peeling of the PSQ-OH film fromthe glass substrate occurred after 2 days at 50 °C and 95% RH. Oppositely, the PSQ-Diol1/EG1 film
did not exhibit cracks or a detachment of the film from the glass substrate even after 1 week at 50 °C
and 95% RH; it possessed a smooth surface (Figure 7). Contrarily, the laser microscope image of the
PSQ-OH film shows the rough surface due to the formation of cracks and the peeling of the film fromthe glass substrate. The time-dependent change in the rms roughness at 50 °C and 95% RH wasmonitored by laser microscopy (Figure 8). The rms roughness of the PSQ-OH film increased from
0.16 μm, exceeded 1.5 μm after 1 day at 50 °C and 95% RH, and exceeded 3.0 μm after 2 days. The
PSQ-Diol1/EG1 film maintained the initial rms roughness within 0.18 μm even after 1 week under thesame conditions. Any changes in the chemical structure were undetected by FT-IR or other methods
after exposure to water vapor at 50 °C and 95% RH for the PSQ-OH and PSQ-Diol1/EG1 films. Whenwater-absorbing antifogging films are exposed to high humidity, the films usually swell and expandin volume, owing to the absorption of water. Thus, the drying process under atmospheric conditions
during the laser microscopy caused the film to shrink. Simultaneously, the polycondensation reactionof the residual silanol groups also promotes the shrinkage of film. The repeated swollen and drying
processes were accompanied by large volume changes that led to the formation of cracks and peelingof the PSQ-OH film. In addition to the inhibition of polycondensation reaction of silanol groups, theflexibility of the tetraethylene glycol chains in the PSQ-Diol1/EG1 film may have prevented theformation of cracks by relaxing the internal stress during the swelling and drying conditions.

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(a)

(b)

Figure 7. Laser microscopy image of the (a) poly[3-(2,3-dihydroxypropoxypropyl)]silsesquioxane(PSQ-OH) film (immersion for 15 h) after exposure at 50 °C and 95% relative humidity (RH) for 1
day and the (b) poly[3-(2,3-dihydroxypropoxypropyl)-co-tetraethylene glycol]silsesquioxane (PSQDiol1/EG1) film (immersion for 15 h) after exposure at 50 °C and 95% RH for 1 day.

Figure 8. Time-dependent change in the root-mean-square roughness at 50 °C and 95% relative
humidity (RH) of the poly[(3-(2,3-dihydroxypropoxypropyl)]silsesquioxane (PSQ-OH) film
(immersion for 15 h) (black circles), poly[3-(2,3-dihydroxypropoxypropyl)-co-tetraethylene
glycol]silsesquioxane (PSQ-Diol1/EG1) film (immersion for 9 h) (light blue circles), and PSQDiol1/EG1 film (immersion for 15 h) (blue circles).

104(3) Transparency of PSQ-Diol1/EG1 film after exposure to water vapor at high temperature
Transparency is also desired for antifogging materials for practical safety; therefore, thetransmittance of the PSQ-Diol1/EG1 film was measured. The transmittance of the PAEAPS film
prepared at 180 °C for 1 h was 91% at 400 nm (Figure 9). The low transmittance of the PAEAPS film
may have been due to denaturation, such as the oxidation of the amino groups on the side chains. The
PSQ-Diol1/EG1 film on a glass substrate exhibited over 99% of transmittance in the wavelength rangeof 400−800 nm. This indicates that the hydroxy groups and tetraethylene glycol in the PSQ-Diol1/EG1
film were thermally stable and oxidation-resistant at high temperatures.

Figure 9. UV–visible spectra of the poly[3-(2,3-dihydroxypropoxypropyl)-co-tetraethylene
glycol]silsesquioxane(PSQ-Diol1/EG1)

film(immersion

for

15

h),

poly[3-(2-aminoethylaminopropyl)]silsesquioxane (PAEAPS) film prior to and after exposure at 50 °C and 95%
relative humidity for 1–2 weeks.

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Changes in transparency under high humidity conditions were investigated. The transmittance at
400 nm of the PAEAPS film decreased from 91% to 86% and 83% after exposure to water vapor at
50 °C and 95% RH for one and two weeks, respectively. Conversely, the PSQ-Diol1/EG1 film retained
a transmittance exceeding 99% at 400 nm even after exposure to the water vapor at 50 °C and 95%
RH for two weeks. As discussed, the color change of the PAEAPS film was derived from the oxidationof amino groups. Under high humidity conditions, the oxidation of amino groups might haveaccelerated in the wet state. In contrast, the PSQ-Diol1/EG1 film showed high oxidation resistance.

4. Conclusions
The PSQ-Diol/EG film was successfully prepared for the application of antifogging materials. The
PSQ-Diol/EG films exhibited a high WU of 15%–19%, which was similar to that of the PSQ-OH film.
From the WU and contact angle measurements, it was observed that the tetraethylene glycol chains of
the PSQ-Diol/EG film were sufficiently hydrophilic to exhibit antifogging abilities. The PSQ-Diol/EGfilm on the glass substrate remained transparent when exposed to water vapor. For the mechanicalproperties, the PSQ-Diol/EG film exhibited a high scratch resistance of 2.4–3.5, which was similar tothat of PSQ-OH film. It was concluded that the introduction of tetraethylene glycol chains did notdecrease the WU and mechanical properties. For durability, the WU of the PSQ-OH film decreased
by repeated exposure to dry and wet conditions at 20% and 95% RH, respectively, at 30 °C, and theformation of cracks was observed by leaving the film to stand at 50 °C and 95% RH. The WU of the
PSQ-Diol/EG film did not decrease, and the formation of cracks was not observed. The space effectof the tetraethylene glycol chains inhibited the residual silanol groups from being condensed, and theflexible chain effect provided film stability upon volume changes during the repeated swelling–drying
processes. Overall, PSQ-Diol/EG exhibited antifogging, scratch resistance, and humidity resistance.

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5. References[1] K.J. Shea, D.A. Loy, Bridged polysilsesquioxanes. Molecular-engineered hybrid organic-inorganic
materials, Chemistry of Materials 13(10) (2001) 3306-3319.
[2] D.A. Loy, K.J. Shea, BRIDGED POLYSILSESQUIOXANES - HIGHLY POROUS HYBRIDORGANIC-INORGANIC MATERIALS, Chemical Reviews 95(5) (1995) 1431-1442.
[3] E. Nam, E.H.H. Wong, S. Tan, Q. Fu, A. Blencowe, G.G. Qiao, Antifogging Surface Facilitated by
Nanoscale Coatings with Controllable Hydrophobicity and Cross-Linking Density, MacromolecularMaterials and Engineering 302(1) (2017) 1600199.
[4]

C.

Zona,

G.

D'Orazio,B.

La

Ferla,

Controlled-Length

Efficient

SynthesisofHeterobifunctionalized Oligo Ethylene Glycols, Synlett 24(6) (2013) 709-712.
[5] R. Guterman, A.R. Kenaree, J.B. Gilroy, E.R. Gillies, P.J. Ragogna, Polymer Network Formation
Using the Phosphane-ene Reaction: A Thiol-ene Analogue with Diverse Postpolymerization Chemistry,
Chemistry of Materials 27(4) (2015) 1412-1419.
[6] A. Bouvet-Marchand, C. Chatard, A. Graillot, G. Boutevin, C. Loubat, D. Grosso, Influence ofexperimental parameters on the side reactions of hydrosilylation of allyl polyethers studied by afractional factorial design, Reaction Chemistry & Engineering 3(5) (2018) 696-706.
[7]

T.

Gunji,Y.

Iizuka,K.

Arimitsu,

Y.

Abe,

Preparation

andproperties

ofalkoxy(methyl)silsesquioxanes as coating agents, Journal of Polymer Science Part a-Polymer
Chemistry 42(15) (2004) 3676-3684.

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Chapter 6: Summary
In summary, the author developed PSQ antifogging materials with hydrophilic groups to achieve ahigh level of water uptake and scratch resistance in antifogging materials. In addition, considering thepractical application of PSQ antifogging materials, the improvement of environmental resistance bydesigning hydrophilic groups was also investigated.
In Chapter 1, the overview of previous studies on antifogging materials and PSQ was given to clarify
the purpose of the thesis.
In Chapter 2, the author investigated whether PSQ films with hydrophilic groups have the potential
as coating materials with both high water uptake and scratch resistance. The PSQ antifogging materialspoly(3-aminopropyl)silsesquioxane (PAPS) and poly(3-(2-aminoethylaminopropyl)silsesquioxane)(PAEAPS) were prepared by sol-gel reactions that are self-catalyzed by the amine moieties of themonomers. The PAPS and PAEAPS films exhibited high water uptakes of 34% and 42%, which are
1.2- and 1.5-times that of the typical antifogging film of PVA, respectively. PAEAPS films exhibitedhigh transparency under humidified conditions. Furthermore, the PAEAPS film exhibited a scratch
resistance 6–7 times higher than that of PVA, as determined by a nanoindenter experiment. The
mechanical property measurement using a nanoindenter indicated that a characteristic feature ofpolysiloxanes whereby flexible Si-O bonds induce recovery from the deformation and thus enhancescratch resistance.
In Chapter 3, the author focused the talk on the amine hydrochloride salt as a hydrophilic group in
PSQ, because the ion is expected to possess stronger interaction with water than neutral polarfunctional groups to develop the high-performance-antifogging materials. The poly[3-(2aminoethylamino)propyl]silsesquioxane hydrochloride (PAEAPS-Cl) films containing aminehydrochloride salt were prepared by immersing the PAEAPS film in 0.5 mol/L HCl methanolic108

solution. FTIR, 13C solid-state NMR and SEM-EDX analysis indicated that the amino group wasconverted to the amine hydrochloride salt upon immersion in 0.5 mol/L HCl methanolic solution for
1 h. The PAEAPS-Cl films showed no cracks or pinholes, and chlorine atoms were homogeneously
distributed on the surface of the PAEAPS-Cl film. The PAEAPS film showed a water uptake andscratch resistance of 22% and 3.2, respectively. The introduction of the amine hydrochloride salt into
the PAEAPS film increased its antifogging property and surface hardness, and the water uptake andscratch resistance of the PAEAPS-Cl film were improved to 29% and 4.3, respectively. However, theamine hydrochloride salt sometimes induced the morphological change of the PAEAPS-Cl film owing
to strong hydration, and cracks and dimples were observed after exposure to water vapor at 40 °C and
95% for 1 h. In contrast, the poly[3-(2-aminoethylamino)propyl-co-methyl]silsesquioxane (P(AEAPco-Me)S-Cl) film exhibited a water uptake of 17%, which was lower than those of the PAEAPS andPAEAPS-Cl films, but the cracks and dimples were not observed for the P(AEAP-co-Me)S-Cl films
even after exposure to water vapor at 40 °C and 95% RH for 1 h. The introduction of the aminehydrochloride salt structure did not decrease transparency. These findings provides the information
for further design and development of antifogging materials with high-performance.
Chapter 4 is focused on hydroxyl groups as hydrophilic groups in PSQ, aiming to develop a colorless
antifogging film. Poly(glycidyloxypropyl)silsesquioxane (PGPS) was successfully synthesized byhydrolysis and polycondensation of 3-glycidyloxypropyltrimethoxysilane using the nitrogen flow
method. To prepare poly(3-(2,3-dihydroxypropoxypropyl)silsesquioxane) (PSQ-OH) film, PGPS wascoated on a glass substrate and immersed in a 0.5 mol/L sulfuric acid for 1–15 h at room temperature,
producing a diol group. The water uptake of the PSQ-OH film increased from 5% to 19% withincreasing immersion time. The PSQ-OH film exhibited a high scratch resistance of 2.7–3.6, similar
to that of a PAEAPS film. The PSQ-OH film was transparent and colorless and exhibited a high109

transmittance of >90% in the wavelength range of 400–800 nm. Unlike the amino-containing PSQ
films, the PSQ-OH film was stable at high temperature and no coloration was observed.
In Chapter 5, the author deals with organically bridged PSQ synthesized from 3glycidyloxypropyltrimethoxysilane and tetraethylene glycol bis(triethoxysilylpropyl)ether (BTESPEG), aiming to suppress degradation under high humidity conditions. A poly[3-(2,3dihydroxypropoxypropyl)-co-tetraethylene glycol]silsesquioxane (PSQ-Diol/EG) film was prepared
via the sol–gel reaction of 3-glycidyloxypropyltrimethoxysilane (GPTMS) and BTESP-EG. From thewater uptake and contact angle measurements, it was concluded that the tetraethylene glycol chains of
the PSQ-Diol/EG film were sufficiently hydrophilic not to suppress the antifogging abilities of PSQOH. For the mechanical properties, the PSQ-Diol/EG film exhibited a high scratch resistance of 2.4–
3.5, which was similar to that of PSQ-OH film. It was demonstrated that the introduction oftetraethylene glycol chains did not decrease the water uptake and scratch resistance. For durability,
the water uptake of the PSQ-Diol/EG film did not decrease, and the formation of cracks was notobserved. The space effect of the tetraethylene glycol chains inhibited the residual silanol groups frombeing condensed, and the flexible chain effect provided film stability upon volume changes during therepeated swelling–drying processes.
In this thesis, the author demonstrates that the development of PSQ antifogging materials with bothwater uptake and scratch resistance are at high level could be achieved by the choice of appropriatehydrophilic groups. In addition, the author clarified that organically bridged PSQ could improve
environment resistance. In the future, PSQ will enable the design of new antifogging materials.

110

List of publications

1. T. Maeda, T. Hamada, S. Tsukada, D. Katsura, K. Okada, J. Ohshita, Antifogging Hybrid Materials
Based on Amino-Functionalized Polysilsesquioxanes, ACS Applied Polymer Materials 3(5)(2021) 2568-2575. (Chapter 2)

2. T. Hamada, T. Maeda, K. Kawashima, T. Sugimoto, A. Tanaka, Y. Tanaka, D. Katsura, S. Mineoi,
Y. Kaneko, J. Ohshita, Effect of the Amine Hydrochloride Salt on the Antifogging Properties ofAmino-Functionalized Polysilsesquioxane, ACS Applied Polymer Materials 5(2) (2023) 1596-1605.
(Chapter 3)

3. T. Hamada, T. Sugimoto, T. Maeda, D. Katsura, S. Mineoi, J. Ohshita, Robust and Transparent
Antifogging Polysilsesquioxane Film Containing a Hydroxy Group, Langmuir 38(18) (2022)
5829-5837. (Chapter 4)

4. T. Maeda, T. Sugimoto, T. Hamada, D. Katsura, S. Mineoi, J. Ohshita, Highly Durable Antifogging
Materials Based on Polysilsesquioxane with Double Hydrophilic Groups: Effect of Bridged
Tetraethylene Glycol Chains in Polysilsesquioxane Films, ACS Applied Polymer Materials 4(10)(2022) 7599-7606. (Chapter 5)This doctoral thesis includes contents reproduced from the papers listed above with permission of the
publishers. Copyright 2021, 2022, and 2023 American Chemical Society.

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Acknowledgments
This thesis is a summary of the author’s studies from 2020 to 2023 under the direction of Professor
Joji Ohshita at Hiroshima University.
I would like to express my gratitude to my supervisor Professor Joji Ohshita for his advice and warm
encouragement. I am also grateful to Lecturer Takashi Hamada for helpful and careful advises. I would
like to thank Professor Toshinori Tsuru, Associate Professor Ichiro Imae, Assistant Professor Yohei
Adachi. I would like to thank Dr. Kazuaki Kawashima, Mr. Susumu Mineoi, Ms. Yuko Tanaka, Mr.
Katsuhiro Horata, Mr. Daiji Katsura, Ms. Sakino Takase, Mr. Sun Weipeng, Ms. Wang Conghuan,
Mr. Takashi Kai, Mr. Keigo Kawakami, Mr. Kei Oshima, Ms. Maho Kurihara, Mr. Mitsuru Sakabe,
Mr. Tetsuya Sugimoto, Mr. Kohei Yamada, Mr. Arata Tanaka, Mr. Takumi Hasegawa, Mr. Tsubasa
Yoshio, Mr. Lin Zhixin, Mr. Shota Terao, Mr. Ryuji Matsuura, Mr. Ryuto Miyazaki for their kindness
and collaboration.

112