Photon Factory Activity Report 2016 #34 (2017)

BL-10C/2016G652

Effects of Bulky End-groups on the Crystallization Rate of Poly(e-caprolactone)
Homopolymers Confined in a Cylindrical Nanodomain
Koshun Kawazu1, Shintaro Nakagawa2, Hironori Marubayashi1, and Shuichi Nojima1,*Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-1552, Japan
2
The University of Tokyo, 4-61-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan

1 Introduction
The crystallization of polymer chains spatiallyconfined in nanodomains is interesting because of theirunique features. [1] In this study, we prepare several
poly(e-caprolactone) (PCL) homopolymers with various
end-groups all confined in an identical nanocylinder
provided by the microphase separation of PCL-blockpolystyrene (PCL-b-PS), where the chain mobility ofconfined PCL chains is expected to change continuously(Fig. 1). The crystallization rate of these PCL homopolymers is examined as a function of the molecular weight ofend-groups ME (or overall mobility of confined chains).
2 Experiment
A PCL-b-PS with a photocleavable o-nitrobenzyl group(ONB) at block junctions was prepared. The PCL blockconfined in nanocylinders was converted into PCL homopolymers by cleaving ONB with UV light. The Tm of PCL
blocks was lower than Tg of PS blocks, so the nanocylinder
was preserved after the photocleavage of ONB owing tothe vitrification of PS matrices. The chain-end of PCL
blocks was replaced with various bulky groups. That is, anacetyl group with ME = 43 g/mol (denoted 0-PCL) in theoriginal PCL block was replaced with adamantine (ME =163, A-PCL), cholesterol(ME = 386, C-PCL), methyl 2,3,6tri-o-benzyl-a-D-galactopyranside (ME = 506, M-PCL),and glassy PS (i.e., original PCL-b-PS) (ME = ∞, PS-PCL).
The microdomain structure was confirmed by smallangle X-ray scattering (SR-SAXS) at BL-10C, KEK-PF.
The crystallization rate of each confined PCL was obtainedby differential scanning calorimetry (DSC).
3 Results and Discussion
The SR-SAXS curves from crystallized samples after
irradiating UV light (denoted X-PCL/PS) are shown in Fig.
Block Chains
Homopolymers
Homopolymers Homopolymers(fixed chain-end) (large end-group) (small end-group) (no end-group)abcd

2. Every curve has several intensity peaks, the positions ofwhich exactly correspond to a ratio of 1 ∶ 3 ∶ 2 ∶ 7 ,indicating the cylindrical microdomain structure is formed.
The primary peak position does not change before and after
irradiating UV light, suggesting the microdomain structure
is completely preserved after photocleavage, andeventually the PCL homopolymers are successfully
confined in the nanocylinder. The nanocylinder diameter
D was evaluated to be 12.9 nm from the interdomain
distance derived from the primary peak position and thevolume fraction of PCL chains.
The inverse of half-time of crystallization 1/t1/2 (ameasure of crystallization rates) is obtained as a functionof ME for confined PCL homopolymers. Surprisingly, 1/t1/2of PCL homopolymers with bulky end-groups (i.e., A-PCL,C-PCL, and M-PCL) is significantly larger than that of 0PCL (with largest chain mobility) and PS-PCL (smallestchain mobility). This result indicates that the crystallization of confined homopolymers depends complicatedlyon their chain mobility as well as D.
610

1510

√3410√3210HighFig. 1. Schematic illustration showing the crystalline block(a) and crystalline homopolymers (b - d) confined in anidentical nanocylinder. The chain mobility of confinedpolymers is expected to increase gradually from a to d.

A-PCL/PS
√710

√3010

2

1C-PCL/PS√710-1√3-2

102

1M-PCL/PS√710-3√3-4

Chain Mobility

21110-50-PCL/PS√71010Low

213Log (Intensity/a.u.)

100.0420.08s (nm-1 )PS-PCL0.120.16

Fig. 2. SR-SAXS curves from crystallized samples
indicated on each curve after irradiating UV light.
References[1] S. Nakagawa et al., Eur. Polym. J. 70, 262 (2015).
* snojima@polymer.titech.ac.jp