Effects of Bulky End-Groups on the Crystallization Kinetics of Poly(ε-caprolactone) Homopolymers Confined in a Cylindrical Nanodomain

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 M_EG = 43 g/mol, original PCL homopolymer), adamantane (M_EG = 163), cholesterol (M_EG = 386), methyl 2,3,6-tri-o-benzoyl-α-d-galacto­pyranoside (M_EG = 506), and vitrified PS (M_EG = ∞, 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 M_EG, 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 ≤ M_EG ≤ 506) was significantly larger than that of original PCL homopolymers (M_EG = 43) and PCL blocks (M_EG = ∞). The crystallization kinetics was discussed by considering the effect of chain mobility on the nucleation mechanism of PCL homopolymers confined in the nanocylinder.