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Isotope Effects on the Crystallization Kinetics of Selectively Deuterated Poly(ε‐Caprolactone)

Li, Lengwan, Chang, Dongsook, Arras, Matthias M. L., Li, Wei, Li, Tianyu, Keum, Jong K., Bonnesen, Peter V., Peng, Xiangfang, Hong, Kunlun
Journal of polymer science 2019 v.57 no.12 pp. 771-779
crystallization, deuterium, differential scanning calorimetry, hydrogen bonding, isotopes, melting point, moieties, polymerization, polymers, supercooling, temperature
Deuterium labeling of semi‐crystalline polymers can dramatically affect their crystallization behaviors. However, the influence of different labeled positions in a partially deuterated polymer on its crystallization is still far from understood. Here, we synthesized a series of selectively deuterated poly(ε‐caprolactones) (PCLs) through ring‐opening polymerization of ε‐caprolactone with controlled deuteration sites, including fully protiated (D0), fully deuterated (D10), tetra deuteration at the 3‐ and 7‐ caprolactone ring positions (D4) and hexa deuteration at the 4‐, 5‐, and 6‐ caprolactone ring positions (D6). All the PCLs showed a similar lamellar structure and parameters. Differential scanning calorimetry (DSC) analysis revealed that the equilibrium melting temperature Tm0, melting temperature Tₘ, crystallization temperature Tc, and crystallization kinetics changed systemically with the deuterium content except for D4, which indicates that the presence of CD₂ moieties on either side of ester group in the polymer chain combined with isotopic inhomogeneity could influence the chain packing. The nonmonotonic trend of Tₘ as a function of deuterium content could be attributed to the difference in a hydrogen‐bond like intermolecular interaction between different PCLs. Partially deuterated PCLs (D4 and D6) showed an Avrami index near 2. After analyzing the parameters at the same supercooling temperature ΔTc, the existence of two crystallization regimes of PCLs were detected. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 771–779