Structure-Scavenging Abilities of 

Cyclodextrin-Based 

Polyurethanes 

by Sandra K. Young, Peter L. Vajda, Eugene Napadensky, 

Dawn M. Crawford, James M. Sloan, and Samuel F. Trevino 

ARL-TR-2776 July 2002 

Approved for public release; distribution is unlimited.
NOTICES 

Disclaimers 

The findings in this report are not to be construed as an official Department of the Army position unless 

so designated by other authorized documents. 

Citation of manufacturer’s or trade names does not constitute an official endorsement or approval of the 

use thereof. 

Destroy this report when it is no longer needed. Do not return it to the originator. 
Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5069 

ARL-TR-2776 July 2002 

Structure-Scavenging Abilities 

of Cyclodextrin-Based 

Polyurethanes 

Sandra K. Young, Peter L. Vajda, Eugene Napadensky, 

Dawn M. Crawford, James M. Sloan, and 

Samuel F. Trevino 

Weapons and Materials Research Directorate, ARL 

Approved for public release; distribution is unlimited. 
ii

Abstract 

Cyclodextrins are ring-shaped molecules containing an apolar cavity with a 

diameter 4–8 Å wide and approximately 8 Å deep. Because of the hydrophilic 

nature of the surface, the materials are readily dispersed in water. However, 

hydrophobic groups on the inner surface of the nanoporous molecules attract 

hydrophobic organics that bind noncovalently to the apolar cavity. Recently, 

polycyclodextrins have been developed as binders for energetic materials and as 

sorbants for biological materials, and exhibit potential for development as 

sorbant materials for water filtration. Studies using these polymers have been 

reported in the literature and show that the polycyclodextrins are very effective 

scavengers of organic contaminants in water. Our work expands on the use of 

cyclodextrins in polymers through the synthesis of several organic cyclodextrinbased polymers. These filtering materials have been shown to scavenge several 

different kinds of contaminants up to parts per million concentrations from 

water. Some neutron work has been done to try to ascertain the nature of 

capture of these contaminants. 
iii

Acknowledgments 

The authors would also like to acknowledge financial support from the U.S. 

Army Research Laboratory (ARL) Director’s Research Initiative (DRI) Program. 

The authors would like to acknowledge the use of the facilities at the National 

Institute of Standards and Technology (NIST) Center for Neutron Research in 

performing all of the 30-m small angle neutron scattering experiments. 
iv

INTENTIONALLY LEFT BLANK.
v

Contents 

Acknowledgments iii

List of Figures vii

List of Tables ix

1. Introduction 1

2. Experimental 5

2.1 Materials.......................................................................................................... 5

2.2 Reference Polyurethane Material Synthesis............................................... 5

2.3 CD-Based Polyurethane Material Synthesis .............................................. 6

2.3.1 Diisocyanate:PEG:CD Materials ..................................................... 6

2.3.2 Diisocyanate:CD Materials .............................................................. 6

2.4 Solubility ......................................................................................................... 6

2.5 FTIR Spectroscopy ......................................................................................... 7

2.6 13C Solid State NMR Spectroscopy .............................................................. 8

2.7 TGA.................................................................................................................. 8

2.8 DSC .................................................................................................................. 8

2.9 Small-Angle Neutron Scattering (SANS).................................................... 8

2.10 Wide-Angle X-ray Diffraction (XRD).......................................................... 9

2.11 High-Performance Liquid Chromatography (HPLC)............................... 9

2.11.1 TNT and RDX Contaminant Samples ............................................ 9

2.11.2 DMMP Contaminant Samples ........................................................ 9

2.12 Scavenging Studies ...................................................................................... 10

2.13 UV/Visible Spectroscopy (UV/Vis).......................................................... 10

3. Results and Discussion 11

3.1 FTIR Studies.................................................................................................. 11

3.2 NMR............................................................................................................... 14
vi

3.3 TGA................................................................................................................ 14

3.4 DSC ................................................................................................................ 15

3.5 SANS.............................................................................................................. 15

3.6 XRD................................................................................................................ 16

3.7 HPLC/Contaminant Scavenging/Renewability Studies....................... 17

4. Conclusions 23

5. References 25

Report Documentation Page 27
vii

List of Figures 

Figure 1. Chemical structure of α (6), β (7), and γ (8) cyclodextrin 

molecules. ................................................................................................................... 1

Figure 2. Chemical structure and carbon labeling of one glucopyranose 

unit............................................................................................................................... 2

Figure 3. Truncated cone structure of cyclodextrins.................................................. 2

Figure 4. Host-guest complexation in cyclodextrin materials. ................................. 3

Figure 5. A general polyurethane synthesis reaction scheme. ................................. 6

Figure 6. Isocyanate monomers (R') used in polyurethane synthesis. .................... 6

Figure 7. Chemical structure of contaminants used in scavenging studies.......... 11

Figure 8. FTIR series for poly(PDI-PEG-CD-41-weight-percent). .......................... 12

Figure 9. FTIR series for poly(TDI-PEG-CD-40-weight-percent)........................... 12

Figure 10. FTIR series for poly(MDI-PEG-CD-32-weight-percent)........................ 13

Figure 11. FTIR series for poly(HDI-PEG-CD-41-weight-percent). ....................... 13

Figure 12. SANS plots of CD, PDI polymer standard, and PDI-PEG-CD 

polymer..................................................................................................................... 16

Figure 13. XRD plots of CD and poly PDI-PEG-CD-41. .......................................... 17

Figure 14. Correlation between different polymers and scavenging ability 

of TNT. ...................................................................................................................... 19

Figure 15. Threading of the CD rings......................................................................... 21
viii

INTENTIONALLY LEFT BLANK.
ix

List of Tables 

Table 1. Solubility testing results for CD monomer and CD-based 

polymers. .................................................................................................................... 7

Table 2. Degradation temperatures (Td) for polyurethane and 

polyurethane-CD polymers. .................................................................................. 15

Table 3. Percent contaminant absorbed from various contaminant solutions 

at various scavenging times................................................................................... 18

Table 4. MDI:CD scavenging studies with RDX....................................................... 20

Table 5. Percent contaminant recovered from the renewability studies............... 22
x

INTENTIONALLY LEFT BLANK. 
1

1. Introduction 

Since their discovery in 1891 by Villiers, cyclodextrins (CDs) have been the 

subject of increasing scientific study. The concentrated focus on CDs is due to a 

combination of their interesting properties and structure. As their name implies, 

CDs are ring-shaped molecules composed of D(+)-glucopyranose units linked 

through α-(1, 4) glycosidic bonds. Cyclodextrins are designated α-, β-, or γ-, 

denoting the number of glucose units as 6, 7, or 8, respectively (Figure 1). 

Cyclodextrins are produced by the enzymatic degradation of starch. The 

resulting product is a mixture of α-, β-, and γ-cyclodextrins, smaller amounts of 

higher analogs, and linear oligosaccharides. Purification is carried out through 

selective precipitation in appropriate solvents [1]. 

O

O

OH

CH2OH

HO

O

O OH

CH2OH

OH

O

OH

CH2OH

O

OH

O

HO O

OH

HOCH2

O

HO

CH2OH

HO

O

OH O

HO

CH2OH

O

O

O

OH

CH2OH

HO

O

O OH

CH2OH

OH

O

OH

CH2OH

O

OH

O O

HO

OH

HOCH2

O

O HO CH2OH

HO

O

HO O

CH2OH

HO

O

O

OH HO

CH2OH O

O O

O

O

O

O

O

O

O O OH HO

CH2OH

O

O

HO

OH

OH

HO

HOCH2

CH2OH

HOCH2

OH

OH

HOCH2

HO

HO

CH2OH

HO

OH

HO

OH

O

O

HO

CH2OH CH2OH

O

OH

Figure 1. Chemical structure of α (6), β (7), and γ (8) cyclodextrin molecules. 

The conformation of the CD ring structure is such that the secondary hydroxyl 

groups, on carbons two and three, are confined to one side of the ring, while the 

primary hydroxyl group on carbon six is restricted to the other side of the ring 

(Figure 2). The glucose rings are slightly tilted from the axis of the ring, with the 

primary hydroxyl groups angled inward. This gives CDs a hollow, truncated 

cone structure (Figure 3). The size of the CD ring increases with the number 
2

Figure 2. Chemical structure and carbon labeling of one glucopyranose unit. 

Figure 3. Truncated cone structure of cyclodextrins. 

of glucose units, the interior minimum diameter for α, β, and γ, cyclodextrins 

being 4.9, 6.2, and 7.9 Å, respectively. The depth of the cavity is constant at 

7.9 Å. 

The positioning of the hydroxyls about the CD gives the exterior a hydrophilic 

character, while the interior is generally apolar or hydrophobic. This fact makes 

CDs excellent candidates for the formation of host-guest complexes. The driving 

force for complex formation can arise from coulombic, dipole-dipole, van der 

Waals, solvatophobic, or hydrogen bonding interactions between the host and 

the guest [2, 3]. These interactions are dependent upon specific molecular 

arrangement of the host and guest. In the case of CD complexes, this generally 

means that at least some part of a hydrophobic guest molecule must fit within 

the CD cavity (Figure 4). Long, thin guests may thread through the CD cavity, 

while more bulky molecules may only partially reside within the cavity. 

Complexes in which the guest molecule is held within the host molecule are 

termed “inclusion compounds,” as opposed to association compounds, where 

the guest lies outside the cavity. However, reversing the complexation and 

removing the contaminants from the CD complex can be accomplished by 

washing the materials with an alcohol.

O

O OH

HO

OH

n

1

3

4

6

O

OH

HO OH

O O

O

O

OH HO

OH HO

OH

OH
3

Figure 4. Host-guest complexation in cyclodextrin materials. 

There are a great number of species that form inclusion complexes with CDs. 

The complexes are usually formed in water, with guests that are marginally 

soluble. Through the formation of a complex, a guest molecule will experience a 

more energetically favorable environment. The hydrophobic moieties of the 

guests prefer to interact with the hydrophobic CDs cavity rather than the solvent, 

while the outer surface of the CDs interacts with the solvent [4]. CDs have also 

been shown to selectively form complexes with one component of a racemic 

mixture [5]. 

Because CDs are natural products produced from a renewable resource and are 

generally non-toxic, much of the research involving CDs is concerned with the 

formation of complexes and their applications many specifically related to 

pharmaceuticals and food processing applications [2, 4, 6, 7]. Improved 

solubility of guest molecules brings significant benefits to drug delivery systems, 

where the active compound may not be soluble in an aqueous solution. CDs 

have been used in the food industry to mask unwanted odors, remove fats, and 

stabilize flavor [3]. In addition to their ability to form useful complexes, CDs are 

of interest for industrial applications. The most viable application for the unique 

host-guest chemistry of the CD molecules lies within the prospect of using the 

cyclodextrins to remove organic contaminants from water. 

Polyurethane polymer synthesis incorporating CD molecules was reported in the 

early 1980s by Shono and coworkers [8–10]. Polyurethane polymers 

incorporating CDs were made from phenylene diisocyanate (PDI) and 2,4-

toluene diisocyanate (TDI). These polymers were then used in chromatography 

columns for separations of solvents with similar boiling points and in the 

separation of aromatic amino acids. In both cases, the polymer was able to 

separate the solvents and small molecules very efficiently. 

More recently, polyurethane materials incorporating CD molecules made from 

1,6-diisocyanatohexane (HDI) and TDI gained more attention when Li and 

coworkers reported the synthesis of “new, novel” nanoporous polymers [11–13]. 

CH3

NO2

N O2

O2N

+

HO

OH

H O

OH

HO O H

H O

OH

HO

O H

H O

O H

H O

O H

HO

O H

HO OH

H O

O H

H O

OH

HO

OH C H3

N O2

NO2

O2N

H2O

EtOH

CD TNT CD-Complex
4

In these polymers, no other glycol unit was used in the polymer, the 

cyclodextrin:diisocyanate ratio was 1:8, and the polymerizations were done in 

dimethylformamide (DMF) at about 70 °C. This work investigated the 

capabilities of the CD-polymers to scavenge contaminants such as 4-nitrophenol, 

toluene, and trichloroethylene (contaminants found in drinking water in many 

places) from water. Li’s work specifically investigated formation constants, ĸ, for 

the inclusion complexes. He discovered that the affinities of the contaminants 

for the CDs within the polymer were some of the highest ever observed 

(108–09 M-1) for noncovalent inclusion phenomena. These researchers theorized 

from their work that while the CD-polymers have a low surface area, they could 

be loaded to a similar extent as activated carbon. The work also revealed that the 

process was a completely reversible process when hydrophobic organic guest 

molecules, such as an alcohol, are used to rinse the material. 

Mach I*

 recently reported synthesis of a variety of CD-based polymers, including 

poly(1-chloro-2,3-epoxy propane)-CD and poly(methylene bis[phenyl isocyanate])(MDI)-CD [14–15]. The purpose of their small business innovative 

research (SBIR) work was to develop materials with explosive that would render 

them less shock sensitive. The cyclodextrin materials did show that they could 

be used to encapsulate energetic materials such as cyclotrimethylenetrinitramine 

(RDX) and that the materials were less shock sensitive. 

In addition, Mach I, Ito and coworkers [16], and Geckeler and coworkers [17] 

looked into the development of CD nanotubes structures. It has been suggested 

that these materials, because of the short spacer groups used to chain them 

together, form well-ordered, nanotube-like structures. In Ito’s work, the CDs 

were molecularly strung onto polyethylene glycol (PEG). In order to prevent 

unstringing of the inclusion complex of the PEG and CDs, bulky groups were 

often covalently attached to the chain ends. Geckeler and coworkers used CDs 

molecularly strung onto the backbone of the polymer chain in order to increase 

solubility of the polymer. None of the research groups verified the well-ordered 

structure through traditional structural techniques, such as small-angle x-ray or 

neutron scattering. 

The goal of this project was to synthesize a series of structurally unique CDbased polyurethane polymers and to then determine the ability of these 

polymers to form host-guest associations based on noncovalent binding of 

organic contaminant molecules. Traditional chemical analyses, such as Fourier 

transform infrared (FTIR), nuclear magnetic resonance (NMR), and thermal 

gravimetric analysis (TGA), were used to characterize the polymers. Testing of 

polymer properties was done by determining the abilities of these polymers to 

scavenge in contaminant solutions of trinitrotoluene (TNT), RDX, and 

dimethylmethylphosphonate (DMMP) and by subsequently testing the 

 *

 Mach I Chemicals, 340 East Church Road, King of Prussia, PA 19406. 
5

“renewability” of the polymers, or how well the polymers can release the sorbed 

contaminant. 

2. Experimental 

2.1 Materials 

β-CD was purchased from Wacker Biochem Corporation.* Tetrahydrofuran 

(THF), DMF, ethanol, methanol, and PDI were purchased from Aldrich Chemical 

Company.†

 Methyl chloride, hexanes, ethylene glycol, polyethylene glycol 

(MW=200, ~3.5 repeat units), ethyl acetate, toluene, MDI, TDI, and HDI were 

purchased from VWR Scientific.‡

 All materials were used as received unless 

otherwise noted. All water used was high-performance liquid chromatography 

(HPLC) grade unless otherwise noted.

2.2 Reference Polyurethane Material Synthesis 

Synthesis of polyurethanes occurs in very straightforward reactions, which 

involve a substitution nucleophilic bimolecular (SN2) reaction between a diol 

and a diisocyanate (Figure 5). Synthesis was performed using polyethylene 

glycol and four different isocyanates (PDI, HDI, MDI, and TDI) as shown in 

Figure 6. While all of these polyurethane materials have previously been 

synthesized by other researchers, it will be useful to have some data to compare 

with our new contaminant scavenging studies [8–18]. Initially, a closed 

atmosphere three-necked reaction flask kept under nitrogen purge was used to 

house the reaction. This method was substituted with a much simpler mixing of 

the chemicals in a beaker and covered with a watch glass. The atmospheric 

purge was not necessary in polyurethane synthesis and by using the threenecked flask, it was much too difficult to remove the product after the synthesis 

was complete. Monomers were added to the beaker and stirred while heating 

(70 °C). Had a catalyst been used, heating might not have been necessary. 

However, since a catalyst could get trapped within the polymer chains and 

contaminate the polymer, no catalyst was used with the experiments. Some of 

the isocyanates (PDI, MDI) were solid; therefore, they required higher 

temperatures, above the melting temperature of the monomer, in the flask in 

order to have good mixing between the diol and diisocyanate. 

 *

 Wacker Biochem Corporation, 3301 Sutton Road, Adrian, MI 49221. 

†

 Aldrich Chemical Company, P.O. Box 2060, Milwaukee, WI 53201. 

‡

 VWR Scientific Products, 405 Heron Drive, P.O. Box 626, Bridgeport, NJ 08014. 
6

Figure 5. A general polyurethane synthesis reaction scheme. 

NCO

OCN

CH3

NCO

OCN OCN NCO

OCN

NCO

3

PDI TDI MDI HDI 

Figure 6. Isocyanate monomers (R') used in polyurethane synthesis. 

2.3 CD-Based Polyurethane Material Synthesis 

Two different CD-based polyurethane polymers were synthesized similarly to 

the reference polymers. 

2.3.1 Diisocyanate:PEG:CD Materials 

For these materials, some CD was substituted for polyethylene glycol. Again, 

while all of these polyurethane-CD materials have previously been synthesized 

by other researchers [8–18], it will be useful to have some data to compare with 

our new contaminant scavenging studies. Three separate CD-based 

polyurethanes were synthesized with each isocyanate, containing different 

amounts of CD: a polyurethane with 3-weight-percent CD, one with 11-weightpercent CD, and one with 40-weight-percent CD. The CD was dissolved in DMF, 

mixed with the other monomers in a 8:1.005:1.005 mole ratio between 

isocyanate:PEG:CD, respectively, leaving an excess of hydroxyl groups, and 

heated in order for the reaction to occur. 

2.3.2 Diisocyanate:CD Materials 

Synthesis was performed using only MDI and CD without the PEG chain 

extender. Four polymers containing different mole ratios of diisocyanate and CD 

were synthesized (6:1—36-weight-percent CD, 4:1—53-weight-percent CD, 3:1—

60-weight-percent CD, and 1:1—82-weight-percent CD). These polymers were 

evaluated with respect to their varying CD content and also enabled a 

comparison between the scavenging properties of MDI-PEG-CD vs. the MDI-CD 

polymers. 

2.4 Solubility 

Solubility was tested on the pure CD material and on all of the polymers 

(reference and 3-weight-percent, 11-weight-percent, and 40-weight-percent) in 

HO R OH + RO N

O

H

R' N O

H

C

O

n

OCN R' NCO
7

13 common solvents (Table 1). Typical solvent groups were used including polar 

organic solvents, halogenated solvents, and non-polar hydrocarbon solvents. 

These included: DMF, THF, ethanol, methanol, hexanes, ether, methyl chloride, 

ethyl acetate, chloroform, toluene, acetone, and water. Approximately 0.5 g of 

polymer was weighed out, added to 20 mL of solution, and allowed to set for 

24 hr. 

Table 1. Solubility testing results for CD monomer and CD-based polymers. 

Material 

Solvent Pure CD PDI-PEG 

With CD 

TDI-PEG 

With CD 

MDI-PEG 

With CD 

HDI-PEG 

With CD 

Water Soluble Insoluble Insoluble Insoluble Insoluble 

Methanol Slightly 

Soluble 

Insoluble Insoluble Insoluble Insoluble 

Ethanol Slightly 

Soluble 

Insoluble Insoluble Insoluble Insoluble 

THF Slightly 

Soluble 

Insoluble Insolublea Insoluble Insoluble 

DMF Soluble Insoluble Insolublea Insoluble Insoluble 

DMSO Soluble Insoluble Insoluble Insoluble Insoluble 

Ethyl 

Acetate 

Slightly 

Soluble 

Insoluble Insoluble Insoluble Insoluble 

Acetone Slightly 

Soluble 

Insoluble Insolublea Insoluble Insolublea 

Ether Slightly 

Soluble 

Insoluble Insoluble Insoluble Insolublea 

Toluene Slightly 

Soluble 

Insoluble Insoluble Insoluble Insoluble 

Hexanes Insoluble Insoluble Insoluble Insoluble Insoluble 

Methylene 

Chloride 

Insoluble Insoluble Insolublea Insoluble Insoluble 

Chloroform Insoluble Insoluble Insolublea Insoluble Insolublea 

a

Standard polymer (polymer without CD) was completely or slightly soluble (swellable) in the 

listed solubility solvent. 

2.5 FTIR Spectroscopy 

Spectra were obtained using a Perkin Elmer Spectrum 2000 FTIR spectrometer. 

Data was collected in a spectral range of 379–4000 cm-1. The number of sample 

scans and resolution were 128 and 4 cm-1, respectively. FTIR spectroscopy yields 

structural information and is used to verify the presence of specific molecules. 

Several references were used to assign details for spectra [19–21]. 
8

2.6 13C Solid State NMR Spectroscopy 

13C NMR spectra were obtained on a Varian Inova 200 spectrometer operating at 

a frequency of 50 MHz for the 13C nucleus. A Doty Scientific 7-mm High-Speed 

CP/MAS probe was used. Ground samples were packed in 7-mm fused zirconia 

rotors (thick walled) and sealed with Kel-FTM caps. Sample spinning rate was 

~3 kHz. Magic angle spinning with high-power decoupling was utilized. The 

number of scans acquired per sample varied but were at minimum 1000 for long 

recycle delays, depending on desired signal:noise. All chemical shifts were 

referenced to TMS. All NMR spectra were evaluated utilizing the 

GRAMS/32 AI Spectral Notebase software version 6.00. NMR spectra yield 

quantitative structural information and are used to determine the precise 

structure of the monomers and/or polymers. 

2.7 TGA 

Experiments were conducted using a TA Instruments TGA 2950 

Thermogravimetric Analyzer. Single scan runs were performed from 20° to 

800 °C at 20 °C/min. Degradation temperatures, Td, are reported as the onset of 

thermal degradation which are calculated using the second derivative plot of the 

TA Instruments Universal Analysis Software. Sample sizes varied between 10 

and 20 mg.

2.8 DSC 

DSC measurements were carried out on 3- to 10-mg samples with a TA 

Instruments thermal analyzer equipped with a liquid nitrogen cooling system. A 

heating rate of 10 °C/min was employed, and an indium standard was used for 

calibration. 

2.9 Small-Angle Neutron Scattering (SANS) 

SANS measurements were performed at the National Institute of Standards and 

Technology (NIST) Center for Neutron Research in Gaithersburg, MD, using the 

30-m SANS spectrometer located at NG-7. 

SANS samples included: (1) TNT-H2O solution, (2) CD powder, (3) CD 

dissolved in water, (4) CD in TNT-H2O solution, (5) poly-PDI-PEG-CD-41 dry, 

(6) solid poly-CD in TNT-H2O solution, and (7) poly-PDI reference. No special 

precautions were taken with the samples (no drying of sample prior to analysis); 

all samples were prepared in a room at 22 °C and 55% relative humidity. 

Samples were enclosed in 1-mm path length quartz cells and maintained at 25.0 

± 0.2 °C. The samples were typically made 24 hr prior to SANS measurements. 

The scattering intensity was measured as a function of q, the magnitude of the 

scattering vector. q is related to the scattering angle, θ, by the relationship 
9

q = 



 





2

sin 4 θ

λ

π , where λ is the wavelength of the incident neutron beam (λ= 6 Å 

for these experiments). The detector was a 64 × 64 cm2 He-3 position-sensitive 

proportional counter with 1-cm2 resolution. Scattered intensity was measured at 

q values ranging from ~0.002 Å-1 to ~0.6 Å-1. This was accomplished by placing 

the detector at various distances from the sample. The positions of the circular 

pinholes before the sample were adjusted to match the resolution of the detector 

configuration. Data were corrected for the scattering from an empty quartz 

sample cell, detector background and sensitivity, and the transmission value of 

each sample. Absolute scattering intensities were obtained by reduction of the 

raw data through calibration with the measured incident neutron intensity. 

2.10 Wide-Angle X-ray Diffraction (XRD) 

X-ray scattering data was collected using a Bruker D5005 powder X-ray 

diffractometer. X-rays are generated using a tube source operated at 40 kV and 

40 mA, with λ = 1.54 Å. Collimation and focusing are achieved with slits and a 

Gobel mirror. 

2.11 High-Performance Liquid Chromatography (HPLC) 

2.11.1 TNT and RDX Contaminant Samples 

Reverse phase HPLC analysis was performed using a Hewlett Packard (HP) 1090 

Series II liquid chromatograph equipped with diode array detector and Luna 

5-μm C18 250 × 4.6-mm column held at 40 °C. Isocratic solvent compositions 

used for TNT analysis were 30% water and 70% methanol. For RDX analysis, 

50% water and 50% methanol were used. Ultraviolet (UV) signals were gathered 

at 230 nm, flow rate was set to 1 mL/min, and injection volume was 20 μL. The 

amounts of contaminant (TNT or RDX) were calculated on comparison of the 

area under the peak (measured at 230 nm, integrated manually) with a 

calibration curve obtained from injecting a solution with a known concentration 

of contaminant. 

2.11.2 DMMP Contaminant Samples 

An HP 5972 gas chromatograph/mass spectrometer (GC/MS) was used to 

analyze samples for DMMP concentration. Experimental conditions were as 

follows: Samples were scanned from 10–200 m/z, the injection port was set to 

250 °C, the transfer line was set to 280 °C, the split was set to 20 mL, the solvent 

delay was 4 min, injection volume was 2 μL and oven temperature programming 

was 50–150 °C at 10 °C/min. The carrier gas was helium and was set at 

~1 mL/min. Amounts of contaminant (DMMP) were calculated on comparison 

with a calibration curve obtained from solutions of DMMP with known 

concentration. 
10

Amount of DMMP in samples was determined based on the area of the peak 

comprised from the sum of all atomic units (au) between 61 and 126 m/z, with 

the baseline drawn at 100-au level. 

2.12 Scavenging Studies 

Stock solutions with known concentrations of TNT, RDX, and DMMP were 

prepared in water (Figure 7). When dissolving explosive contaminants, there are 

issues concerning solubility. These solubility difficulties lead to different 

standard concentrations in the three stock solutions (TNT—19.4 ppm, 

RDX—13.04 ppm, and DMMP—20.9 ppm). Four polymers (PDI-PEG-CD-41-

weight-percent, HDI-PEG-CD-40-weight-percent, MDI-PEG-CD-32-weightpercent, and TDI-PEG-CD-40-weight-percent) were individually tested for 

scavenging ability in each of the stock contaminant solutions. Prior to 

performing the scavenging studies, the polymers were purified to remove any 

excess reactants or possible contaminants. The polymers were allowed to set in 

water for four days before being filtered and soaked in ethanol for 3 hr. The 

polymers were then allowed to dry overnight. Fifty milliliters of the stock 

contaminant solution and 0.5 g of polymer was added to a 150-mL beaker. The 

polymer-charged solution was then stirred for 3 hr. The polymer-contaminant 

solution was then filtered, and the filtrate was analyzed using HPLC to 

determine the amount of remaining contaminant in the water. To determine the 

ability of the complexed polymers to release contaminant molecules, the 

complexed polymers were placed in ethanol (exact amount varies) and stirred for 

1 hr. The polymers were then filtered from the ethanol solution, and the ethanol 

filtrate was analyzed using HPLC. The HPLC analysis provides a quantitative 

evaluation of how much contaminant the CD polymers can scavenge from 

solutions and the degree that the complexation with the polymers can be 

reversed by rinsing in alcohol. In separate evaluations, an 18-hr test and a 44-hr 

test were performed with TNT to determine whether increased exposure to the 

contaminant would increase the scavenging uptake of the CD. The ethanol wash 

served to determine the degree of renewability the polymers possessed. By 

analyzing the ethanol used to rinse the polymers, the degree to which these 

polymers can release their captured contaminants and create space for new 

contaminants could be assessed. 

2.13 UV/Visible Spectroscopy (UV/Vis) 

UV/Vis measurements were conducted with a dispersive UV-Vis-NIR 

spectrophotometer, possessing a R928 photomultiplier tube. Samples were put 

into Sabia liquid cells, which absorb in the 2100- to 2500-nm range (not 

interfering with the sample absorbance). Samples were scanned between 190 

and 750 nm at a scan rate of 200 nm/min. Only TNT samples were run to 

compare the UV/Vis method with the HPLC method. 
11

Figure 7. Chemical structure of contaminants used in scavenging studies. 

3. Results and Discussion 

Initially, polymer synthesis for PDI and TDI polymers was performed identically 

to that used by Li and coworkers, using a CD:diisocyanate ratio of 1:8 [12, 13]. 

These polymers, however, showed no solubility in any of the variety of solvents 

planned for the solubility studies. It is common in polyurethane synthesis to use 

a diol molecule as a spacer unit. As the length of the spacer unit increases, often 

so does the solubility of the polymer material. Polyethylene glycol was chosen as 

an initial candidate as a spacer unit because it is cheap, readily available, and can 

be obtained in many different molecular weights. The results for the solubility 

studies for the polymer materials using polyethylene glycol are shown in Table 1. 

The use of polyethylene glycol did not appear to help the solubility of the 

polymeric materials, as all polyurethane-CD materials are insoluble. A 

discussion of possible reasons for the lack of solubility will be given later in this 

report. Some of the polymer standards, those made without cyclodextrin, had 

limited solubility in the range of solvents for the solubility tests but they are not 

listed here due to space constraints. The polyurethane-CD materials noted with 

a superscript “a” indicate that the standard polymer (the polymer without CD) 

was completely or slightly soluble (swellable) in the listed solubility solvent. 

3.1 FTIR Studies 

For all four polyurethane-CD materials synthesized in the current experiments, 

the FTIR spectrum for the polymer has some notable differences from the spectra 

of their reactants. Since all four polyurethane-CD materials have similar 

changes, a general discussion will be included rather than discussion of each 

individual set of spectra. The FTIR series for poly(PDI-PEG-CD-41-weightpercent) is shown in Figure 8, the poly(TDI-PEG-CD-40-weight-percent) series is 

shown in Figure 9, the poly(MDI-PEG-CD-32-weight-percent) series is shown in 

Figure 10, and the poly(HDI-PEG-CD-41-weight-percent) series is shown in 

Figure 11. The spectra in the figures are offset in order to observe details of the 

materials, and the spectra indicate that the synthesis was successful. The 

CH3

NO2

NO2

O2N

TNT 

N

N

N

NO2

NO2

O2N

RDX 

H3C P

OCH3

OCH3

O

DMMP
12

4000 3500 3000 2500 2000 1500 1000 500

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1711 cm-1

-C=O stretch

1503 cm-1

2

o

-N-H 

Polymer

2

o

-N-H and -O-H

stretching

2270 cm-1

-N=C=O

-C-H

stretch

3330 cm-1

hydrogen bonded

-O-H stretch

PDI

Poly-PDI-41

CD

PEG

Intensity (plots offset)

Wavenumbers (cm-1)

Figure 8. FTIR series for poly(PDI-PEG-CD-41-weight-percent). 

4000 3500 3000 2500 2000 1500 1000 500

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

Polymer

2

o

-N-H and -O-H

stretching

1711 cm-1

-C=O stretch

2270 cm-1

-N=C=O

1503 cm-1

2

o

-N-H 

3330 cm-1

hydrogen bonded

-O-H stretch

-C-H

stretch

Poly-TDI-40

TDI

CD

PEG

Intensity (plots offset)

Wavenumbers (cm-1)

Figure 9. FTIR series for poly(TDI-PEG-CD-40-weight-percent). 

Intensity (plots offset) 

Wavenumbers (cm-1)
13

4000 3500 3000 2500 2000 1500 1000 500

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

1503 cm-1

2

o

-N-H 

1711 cm-1

-C=O stretch

MDI

Poly-MDI-32

CD

PEG

2270 cm-1

-N=C=O

-C-H

stretch

Polymer

2

o

-N-H and -O-H

stretching

3330 cm-1

hydrogen bonded

-O-H stretch

Intensity (plots offset)

Wavenumbers (cm-1)

Figure 10. FTIR series for poly(MDI-PEG-CD-32-weight-percent). 

4000 3000 2000 1000

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

Poly-HDI-41

HDI

CD

PEG

1730 cm-1

-C=O stretch

Polymer 2o-N-H

and -O-H stretching

2270 cm-1

-N=C=O

-C-H

stretch

3330 cm-1

hydrogen bonded

-O-H stretch

Intensity (plots offset)

Wavenumbers (cm-1)

Figure 11. FTIR series for poly(HDI-PEG-CD-41-weight-percent). 
14

disappearance of the isocyanate peak (2270 cm-1) indicates that all the isocyanate 

groups were used in the reaction. The appearance of amide C=O (1711 cm-1), 

N-H band of a secondary amide (1503 cm-1) (amide II), and a C-N stretching 

band (1280 cm-1) indicate that the polymer was formed. Typically, disappearance 

of the hydroxyl groups (3330 cm-1) would also be observed and would indicate 

that the reaction went to completion but, in this case, the CD monomer has 21 

hydroxyl groups per molecule but the isocyanate was the limiting reagent and 

not all hydroxyls were used in the reaction in an effort to keep crosslinking to a 

minimum. Therefore, the broad band at 3300–3500 cm-1 is indicative of both 

hydrogen bonded hydroxyl groups and secondary amide groups. Most of these 

features have previously been reported in the literature [13, 22]. 

3.2 NMR 

NMR spectra were taken of the TDI-PEG polymer standard and TDI-PEG-CD-40-

weight-percent polymer. Polymer spectra contain notoriously broad peaks that 

are difficult to extract quantitative data from. However, both spectra did contain 

peaks indicating various carbon groups including benzene rings, methyl and 

methylene groups, and methylene groups attached to hydroxyl groups. 

However, we were unable to resolve these peaks and therefore were unable to 

show distinction between the different sites of reactivity. Because the peaks were 

so broad and no useful data was extracted, the NMR spectra will not be shown 

here. 

3.3 TGA 

TGA was performed on the polymeric materials that were synthesized with and 

without CD. The onset temperatures of degradation (Td) are shown in Table 2. 

Td’s for the polymers were measured using the TA Instruments Universal 

Analysis software. The peak maximum of the second derivative plot (of the 

primary weight loss transition) was used to determine Td. The onset of thermal 

degradation of β-CD was measured at 371 °C. The Td’s measured for the 

polyurethanes (with 0% CD) ranged between 320° and 398 °C. Because the onset 

degradation of the polyurethanes is in the same general region as the β-CD, it is 

difficult to discern what chemical component of the CD-based polyurethane 

contributes to changes observed in thermal stability. The various polymers 

exhibit changes in Td with regard to CD content, however, a general trend in Td

was not observed. Variability in the Td values can be explained by the varying 

rates of thermal degradation (slope and breadth of the weight loss transition) for 

the different polymers as well as variations in post synthesis drying conditions. 
15

Table 2. Degradation temperatures (Td) for polyurethane and polyurethane-CD 

polymers. 

Onset Td 

(°C) 

Weight-Percent CD in Polymer Polymer 

0% CD 3% CD 11% CD 32% CD 40% CD 

PDI-PEG 320 323 375 — 274 

TDI-PEG 371 346 376 — 372 

HDI-PEG 398 369 361 — 368 

MDI-PEG 367 394 409 404 — 

3.4 DSC 

DSC was taken of PDI-PEG, PDI-PEG-CD 11%, and PDI-PEG-CD 41% samples. 

For all of the samples, no glass transition or crystallization temperatures were 

apparent, and the experiment was performed below sample degradation 

temperatures. A crystallization temperature was apparent in the pure CD 

thermogram. Incorporation of the CD into the polymer must repress the 

crystallinity of the CD molecules. Since no significant thermal trends were 

observed via DSC measurements, thermograms are not included in this report. 

3.5 SANS 

Many groups have previously hypothesized organization of the CD within the 

polymer chains [15, 16]. One hypothesis reported for CD research stated that 

CDs could pick up more contaminants in a polymer structure because the CD 

molecules would “line up” in the polymer chains, creating an ordering of the 

polymer [12, 13]. While this theory has never been proven, one of the best ways 

to study such ordering in polymer systems is through the use of small-angle 

scattering. 

SANS plots were obtained for: (1) TNT-H2O solution, (2) CD powder dry, (3) CD 

dissolved in water, (4) CD in TNT-H2O solution, (5) poly-PDI-PEG-CD-41 dry, 

(6) solid poly-CD in TNT- H2O solution, and (7) poly-PDI reference. The TNTH2O solution, CD powder dry, CD dissolved in water, CD in TNT-H2O solution, 

and poly-PDI reference samples did not show any significant scattering features. 

The CD powder dry and poly-PDI reference samples can be seen in Figure 12. 

The poly-PDI-PEG-CD-41 dry sample does show Bragg scattering. Bragg 

scattering is an indication of ordering within a system. The Bragg peak observed 

in the cyclodextrin-polymer was fit with a Gaussian, which had an intensity 

value (m1) of -0.015236, a peak position (m2) of 0.085057, a standard deviation 

(m3) of -0.02668, and a correlation value (r) of 0.99411. From this fit, the 

d-spacing can be calculated from the peak position, or q value, using the 
16

Figure 12. SANS plots of CD, PDI polymer standard, and PDI-PEG-CD polymer. 

following equation: q = (sin ) 4 θ

λ

π

 = 

d

2π , where q is the peak position, λ is the 

wavelength mof the scattering, θ is the angle of the scattering, and d is the 

d-spacing. The d-spacing was found to be 73.87 Å (7.39 nm) or possibly about 

nine ordered cyclodextrin molecules. This is about double the length of a PEG 

unit. 

The presence of Bragg spacing in the poly-PDI-PEG-CD-41 dry sample is 

significant. While ordering in these polymer systems had been hypothesized, it 

had never before been reported in any published reports. In addition, this longrange ordering is not present in the small molecule CD SANS plot or the polyPDI reference sample SANS plot. This further indicates a significant degree of 

ordering of the poly-PDI-PEG-CD-41 dry sample over the other materials. What 

remains a mystery is how these systems could force such ordering since the 

materials are extremely crosslinked, rigid polymers. However, the scavenging/ 

renewability studies may be able to shed some light on this issue. 

3.6 XRD 

The idea of using XRD as a technique to study the cyclodextrin polymers was 

brought about because of the possible need to follow the trapping ability of the 

materials. Following the changes in crystallinity and crystal structure is one way 

to do this. 

0.1

1

10

0.01 0.1

I

q

CD

PDI Polymer

Standard

Poly-PDI-PEG-CD-41

Intensity (Offset) 

q 
17

XRD was performed on CD and poly-PDI-PEG-CD-41 samples. CD monomer 

molecules exhibit a high degree of crystallinity and hydrogen bonding between 

samples. This is observed in Figure 13, containing plots of both the CD and polyPDI-PEG-CD-41 samples. Here, it can be observed that when the CD is 

incorporated into a polymer system it completely disrupts the fine structure 

crystallinity of the CD materials. Only one peak is still observable at 

approximately 2θ = 18. By using the Bragg equation, a d-spacing of 2.49 Å can be 

calculated. This does not correspond to the diameter or depth (6.2 and 7.9 Å, 

respectively) of the β-CD and it is larger than a single C-C bond (1.54 Å). 

Apparently, some small-range crystalline ordering is occurring, and the 

ordering, evident from the broad peak, is polydisperse. 

Figure 13. XRD plots of CD and poly PDI-PEG-CD-41. 

3.7 HPLC/Contaminant Scavenging/Renewability Studies 

All standard polymers (no cyclodextrin added) were treated, soaked in 

contaminant solutions and then tested for any “scavenging” capabilities. While 

no scavenging capabilities were expected, it is necessary to test the standard 

polymers to ensure that no other trapping factors are involved with the real 

results. Insignificant amounts of contaminant solution were absorbed by the 

non-CD polymers and, therefore, none of the data will be shown here. 

0 20 40 60 80 100

0

100

200

300

400

500

600

Poly PDI-PEG-CD-41

Cyclodextrin

Molecule

Intensity (offset)

2θ
18

Recall that all polyurethane-CD materials were soaked in TNT solutions for 3-, 

18-, and 44-hr periods. See Table 3 for the resulting data from all of the 

contamination scavenging studies. The tabulated data shows the weight percent 

of contaminant absorbed from the dilute aqueous solutions. 

Table 3. Percent contaminant absorbed from various contaminant solutions at various 

scavenging times. 

Contaminant/Scavenging Time (hr) Polymer Sample 

TNTa/3 TNTa/18 TNTa/44 RDXb/3 DMMPc/3 

PDI-PEG-CD 41-weight-percent 

n

HO OH

OH

OH

HO

O

O

HO

OH

N

H

N

O

H

O

48% 66% 69% 36% 21% 

TDI-PEG-CD 40-weight-percent 

n

HO OH

OH

OH

HO

O

O

HO

OH

N

H

N

O

H

O

CH3

43% 65% 74% 30% 16% 

MDI-PEG-CD 32-weight-percent 

HO OH

OH

OH

HO

O

O

HO

OH

N

O

H

O H

N

n

8% 16% 29% 2% 4% 

HDI-PEG-CD 41-weight-percent 

HO OH

OH

OH

HO

O

O

HO

OH

N

O

H

O

H

N

n

5% 10% 16% 2% 3% 

a

Starting contaminant concentration: 19.4 ppm. 

b

Starting contaminant concentration: 13.04 ppm. 

c

Starting contaminant concentration: 20.9 ppm. 

In the 3-hr studies, HPLC revealed that the TNT concentration was nearly halved 

after exposure to two of the polyurethane-CD polymers with cyclodextrin 

additions (PDI-PEG-CD and TDI-PEG-CD), while the remaining two polymers 

(HDI-PEG-CD and MDI-PEG-CD) retrieved insignificant amounts of TNT. A 

preliminary examination of the tabulated data for the four polymer-contaminant 

solution systems revealed that the two polymers that proved to be effective in 

scavenging the contaminants were far better dispersed throughout the water. 

Originally, the theory was that the results may have been the result of finer 
19

grinding, as the two effective polymers were ground down to a powder leaving a 

greater surface area exposed to the contaminant solution, while the other two 

polymers consisted of slightly larger particles. However, both polymers were 

reground to a fine powder and still produced the same results. It is more likely 

that the molecular structure of the polymers played a significant role in the 

scavenging ability. An examination of the four structures of the polymers used 

in the scavenging study demonstrates that the two polymers (PDI-PEG-CD and 

TDI-PEG-CD) most effective at scavenging have very similar structures, whereas 

the two less effective polymers have very different structures (see Figure 6). 

As might be expected, the 18- and 44-hr TNT studies reported increasingly better 

absorption for all polymers. The difference between 3- and 44-hr scavenging 

times is significant enough to suggest that the contaminants used in this study 

are not easily attracted to the hydrophobic cavity of the CD, at least when it is 

covalently bound to the polymer (Figure 14). With increased solution, the 

contaminant exposure in the molecules have more time to “find” the CDs in the 

polymer. However, then we might assume that in a little less than 2 days 

(44 hr) there would be plenty of time for all of the contaminants to be absorbed 

by the polyurethane-CD material and, that beyond this, it would be impractical 

for an actual membrane to be used for contaminant scavenging. 

Figure 14. Correlation between different polymers and scavenging ability of TNT. 

20

40

60

80

100

120

-10 0 10 20 30 40 50

% TNT (100% = 19.4 ppm)

Exposure Time (hr)

MDI-PEG-CD-32

HDI-PEG-CD-40

PDI-PEG-CD-41

TDI-PEG-CD-40
20

For these scavenging experiments, a significant excess of moles of CD to moles of 

contaminants (41:1) were used in each of the experiments, which should yield 

many opportunities for capture by CD molecules incorporated into the 

polyurethane. In addition, previous researchers have shown that CD polymers 

exhibit strong interactions with guest molecules, which contain π electrons 

and/or heteroatoms [9]. However, even in the 44-hr TNT solution exposure 

experiment there is still only 70–75% uptake of the contaminants from the 

solution for the PDI and TDI urethane polymers. 

The 3-hr RDX and DMMP studies showed results similar to the TNT 3-hr study. 

The two similar polyurethane-CD structures (PDI-PEG-CD and TDI-PEG-CD) 

scavenged the RDX and DMMP solutions better than the two structures that 

were structurally unique in the experiment. In these experiments, the amount of 

contaminants scavenged from solution was significantly less than the 3-hr TNT 

studies. This is particularly surprising for RDX, which while not conjugated has 

a very similar chemical composition and structure. However, if recalling 

previous experiments by other researchers, guest molecules containing π

electrons (conjugated systems) are much more likely to be absorbed by the CD 

molecules [9]. Therefore, it is reasonable that more TNT was absorbed as 

opposed to RDX or DMMP. 

Table 4 shows the scavenging results for the MDI-CD polymers synthesized 

without the PEG chain extender. The data shows that the MDI-CD polymers 

exhibited much higher scavenging ability compared to the MDI-PEG-CD 

polymers. For these polymers, the RDX absorbed by the polymers increased 

with decreasing CD content. This suggests that CD content may not be as 

important as chemical structure for optimized scavenging ability. When the 

MDI-CD polymer containing approximately 36% CD is compared with the MDIPEG-CD polymer (32% CD), the amount of RDX absorbed from solution 

increases from 2% (MDI-PEG-CD) to 64% (MDI-CD). 

Table 4. MDI:CD scavenging studies with RDX. 

Polymer 

Weight-Percent 

CD Mole Ratio 

(MDI:CD) 

Weight-Percent 

RDX Scavenged 

From Water 

(20 hr) 

Weight-Percent 

RDX Released by the 

Complexed Polymer 

Following Ethanol Wash 

MDI-CD 82 1:1 19 29 

MDI-CD 60 3:1 51 46 

MDI-CD 53 4:1 61 78 

MDI-CD 36 6:1 64 40 

In order to gain a better understanding of the scavenging results, several possible 

explanations should be considered. Because of the high degree of crosslinking, 

the polymer chains will not have much free volume. How does this impact the 
21

ability of these polymers to scavenge contaminants from solution? The inability 

for the polymer chains to reorganize themselves through free volume effects or 

gyrations in the solution will restrict the contaminant molecule’s ability to access 

all parts of the polymer chain. Therefore, one possibility is that the CDs were 

inaccessible to the contaminants, resulting in their inability to scavenge many 

molecules from solution. 

Because of similarities, it is important to note that we are not suggesting that our 

polymers are forming inclusion complexes with the CDs. Harada and coworkers 

have previously reported that polyethylene glycol will not form inclusion 

complexes with β-CDs [23]. However, a valid possibility for these reactions is 

the ability of α-CDs to cause threading of materials, including PEG [16]. These 

systems are essentially molecular “nanotubes” where the CD is threaded onto 

the PEG chains. While β–CDs have been reported to not form inclusion 

complexes easily with PEG because of their larger size, threading of PEG 

molecules has been reported with α-CDs [24], and threading of β–CDs has been 

reported with other hydrophilic materials including ethers, amines, and 

poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) triblock copolymers 

(PEG-PPG-PEG) [25, 26]. Therefore, for the reported experiments in solution, it is 

possible the CD had sufficient time before reaction to form molecular nanotubes 

with the PEG or the isocyanate endgroup and then was trapped as the material 

polymerized (Figure 15). This would render a fraction of the CDs unavailable for 

scavenging contaminants. This might also explain the high degree of ordering 

observed in the SANS results. This is an observation, previously, unexplained, 

especially for these rigid polymer systems. A series of CD molecules strung on 

PEG would be forced to line up and would reduce the scavenging abilities. The 

only way to validate this theory would be to perform more SANS experiments, 

including some on the isocyanate:CD (no PEG) systems. This might help explain 

the inability of the polymers to obtain 100% scavenging but would still not 

address the wide discrepancy between the PDI and TDI polymer systems, which 

had ~40–75% scavenging, and the MDI and HDI polymer systems, which had 

~5–30% scavenging. 

Figure 15. Threading of the CD rings.
22

For the renewability studies, the working hypothesis based on previous work by 

other researchers was that CDs would easily release the contaminants, yielding 

“renewed” materials that could be reused. In these works, no correlation was 

made based on polymer structure and all renewability studies were performed 

for an equal period of time. Interestingly, the results were not consistent 

(Table 5), i.e., the polymers with scavenged TNT did not all release an equal 

amount of TNT. The tabulated data for the renewability study describes the 

percent of contaminant recovered from being trapped within the polyurethaneCD. The percentage of contaminant retrieved by the alcohol wash varied with 

each study performed and with each polymer in the study. In the renewability 

studies, MDI and HDI polymers performed the best, easily releasing the most 

contaminant consistently. However, recall that these structures scavenged the 

least amount of contaminants. 

Table 5. Percent contaminant recovered from the renewability studies. 

Contaminant/Scavenging Time (hr) Polymer Sample 

TNT/3 TNT/18 TNT/44 RDX/3 DMMP/3 

PDI-PEG-CD 41-weight-percent 

n

HO OH

OH

OH

HO

O

O

HO

OH

N

H

N

O

H

O

69% 66% 37% 66% 0% 

TDI-PEG-CD 40-weight-percent 

n

HO OH

OH

OH

HO

O

O

HO

OH

N

H

N

O

H

O

CH3

51% 49% 38% 51% 0% 

MDI-PEG-CD 32-weight-percent 

HO OH

OH

OH

HO

O

O

HO

OH

N

O

H

O H

N

n

86% 81% 23% 90% 0% 

HDI-PEG-CD 41-weight-percent 

HO OH

OH

OH

HO

O

O

HO

OH

N

O

H

O

H

N

n

100% 87% 51% 100% 0% 

It is interesting that the 44-hr TNT studies, having the most contaminant trapped 

within the structure, appear to be the most stable, resisting the release of 

contaminants. This is not understood. Out of all of the materials, only the HDI-
23

PEG-CD-41 polymers were fully “renewed.” This contradicts predictions and 

results from previous work by other research groups [12, 13]. Perhaps, while the 

complexed polymers are stirred in ethanol and the contaminant is being washed 

out of the CD structure, there still are forces drawing it back into the polymer. It 

might be more feasible to perform a diffusion wash where the ethanol would 

flow through the polymer, continuously removing contaminant molecules and 

preventing rediffusion of the contaminant into the CD. However, it is likely that 

renewability might be optimized by utilizing a less crosslinked polymer 

structure where accessibility of the CD molecules are maximized, facilitating 

both the sorption and desorption of complexed molecules to occur. 

UV/Visible spectroscopy can often be performed in coordination with HPLC 

experiments. UV/Vis is particularly useful because samples are analyzed 

quickly (in seconds), experimentation is nondestructive to the sample and 

provides quantitative information regarding concentrations of conjugated 

molecules in solution. The polymers in our studies contain conjugation and 

could interfere with a UV/Vis study by causing additional peak appearances. A 

quick analysis of several polymers in solutions confirmed this. By inserting the 

polymers in with trapped contaminants into solution and quickly analyzing the 

results, it was evident that the presence of the conjugation in the polymers was 

causing the results to be superficially high. Therefore, UV/Vis is not an 

adequate technique in the analysis of these systems. 

4. Conclusions 

Structurally unique polyurethane-CD polymers were synthesized, characterized 

by traditional polymer techniques, and properties evaluated for scavenging 

ability of contaminants from water and ability to renew the materials through 

rinsing. Two of the PEG polymers with similar chemical structures (PDI-PEGCD and TDI-PEG-CD) possessed far greater scavenging capabilities than the 

other two polymer systems (MDI-PEG-CD and HDI-PEG-CD). A likely cause of 

this is lack of accessibility of the contaminant to the polymer chains due to 

reduced polymer free volume combined with CDs possibly threaded onto the 

polymer chains, rendering them unavailable for scavenging contaminant 

molecules. Threading of PEG might be a good explanation for the discrepancies 

between MDI-PEG-CD polymer and the MDI-CD polymer. When PEG was not 

used in the polymerizations, the scavenging abilities increased significantly. 

These issues might be addressed in future work by trying a different chain 

extender (not polyethylene glycol), by trying to control and therefore reduce the 

degree of crosslinking, or by using a polymer material possessing greater free 

volume in a wide range of solvents, such as polyesters. Other future work might 
24

include studying the source of the long-range ordering in the system, as 

observed using SANS. While these materials were neither optimized nor usable 

directly for applications, a more optimized system could hold promise for 

improving water treatment technologies. 
25

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22. Rusa, C. C., C. Luca, and A. E. Tonelli. “Polymer-Cyclodextrin Inclusion 

Compounds: Toward New Aspects of Their Inclusion Mechanism.” Macromolecules,

vol. 34, pp. 1318–1322, 2001. 

23. Harada, A., and B. Zsadon. Comprehensive Supramolecular Chemistry. New York: 

Elsevier Science Ltd., chapter 19, p. 574, 1996. 

24. Dagani, R. “Polymer Chains Threaded With Many Cyclodextrin Rings.” Chemical 

and Engineering News, pp. 39-40, April 1992. 

25. Samal, S., B.-J. Choi, and K. E. Geckeler. “The First Water-Soluble Main-Chain 

Polyfullerene.” Chemical Communications, pp. 1373–1374, 2000. 

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Macromolecular Theory and Simulation, vol. 9, pp. 759–771, 2000.
cyclodextrins, polyurethanes, water treatment, HPLC, scavenging studies, TNT, RDX, 34

DMMP, renewability

Cyclodextrins are ring-shaped molecules containing an apolar cavity with a diameter 4-8 Å wide and approximately 8 Å

deep. Because of the hydrophilic nature of the surface, the materials are readily dispersed in water. However,

hydrophobic groups on the inner surface of the nanoporous molecules attract hydrophobic organics that bind

noncovalently to the apolar cavity. Recently, polycyclodextrins have been developed as binders for energetic materials

and as sorbants for biological materials, and exhibit potential for development as sorbant materials for water filtration. 

Studies using these polymers have been reported in the literature and show that the polycyclodextrins are very effective

scavengers of organic contaminants in water. Our work expands on the use of cyclodextrins in polymers through the

synthesis of several organic cyclodextrin-based polymers. These filtering materials have been shown to scavenge

several different kinds of contaminants up to parts per million concentrations from water. Some neutron work has been

done to try to ascertain the nature of capture of these contaminants.

ARL-TR-2776

U.S. Army Research Laboratory

ATTN: AMSRL-WM-MA

Aberdeen Proving Ground, MD 21005-5069

Sandra K. Young, Peter L. Vajda, Eugene Napadensky, Dawn M. Crawford, 

James M. Sloan, and Samuel F. Trevino 

Structure-Scavenging Abilities of Cyclodextrin-Based Polyurethanes 622105.H84

July 2002 Final, October 2000 – October 2001

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