Effects of Bulky End-Groups on the Crystallization Kinetics of Poly(ε-caprolactone) Homopolymers Confined in a Cylindrical Nanodomain
2017
Kawazu, Koshun | Nakagawa, Shintaro | Ishizone, Takashi | Nojima, Shuichi | Arai, Daiki | Yamaguchi, Kazuo | Nakahama, Seiichi
We examined the isothermal crystallization kinetics of poly(ε-caprolactone) (PCL) homopolymers confined in a cylindrical nanodomain (nanocylinder) with 12.9 nm in diameter. The confined PCL homopolymers were prepared using the microphase separation of PCL-block-polystyrene (PCL-b-PS) diblock copolymers with a photocleavable o-nitrobenzyl group (ONB) at block junctions and the subsequent cleavage of ONB with UV light. Several PCL homopolymers with different end-groups, acetyl group (molecular weight MEG = 43 g/mol, original PCL homopolymer), adamantane (MEG = 163), cholesterol (MEG = 386), methyl 2,3,6-tri-o-benzoyl-α-d-galactopyranoside (MEG = 506), and vitrified PS (MEG = ∞, i.e., PCL blocks in PCL-b-PS), were prepared to gradually change their chain mobility in the nanocylinder. The crystallization rate of corresponding bulk PCL homopolymers (i.e., no spatial confinement imposed) decreased steadily with increasing MEG, suggesting that these end-groups had no extra effect on the crystallization but simply reduced the chain mobility of PCL homopolymers. The time evolution of crystallinity for all the confined PCL chains showed first-order kinetics, indicating the overall crystallization was driven by homogeneous nucleation. The crystallization rate of confined PCL homopolymers with bulky end-groups (163 ≤ MEG ≤ 506) was significantly larger than that of original PCL homopolymers (MEG = 43) and PCL blocks (MEG = ∞). The crystallization kinetics was discussed by considering the effect of chain mobility on the nucleation mechanism of PCL homopolymers confined in the nanocylinder.
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