Crystallization of poly(α‐methyl‐α‐N‐propyl‐β‐propiolactones) prepared from homogeneous and heterogeneous initiators

Half‐crystallization times t½, enthalpies of fusion ΔH, melting temperatures Tf glass transition temperatures Tg x‐ray patterns, and morphologies were obtained for nine samples of poly(α‐methyl‐α‐n‐propyl‐β‐propiolactones) prepared from different homogeneous or heterogeneous initiators. The bulk of the results indicates that all samples can be classified into two categories: Polymers A having t½≏, 100 min, ΔH ≏ 26 J/g, T ≏ 376 K, Tg ≏ 275 K, and Polymers B having t½ ≏ 10 min, ΔH ≃ 14.5 J/g T ≏ 425 K and Tg ≏ 271 K. Polymers A were prepared with homogeneous initiators while polymers B were polymerized with heterogeneous intiators. The difference in crystallization behavior between polymers A and polymers B is certainly due to a difference in microstructure, brought about by the initiators, which has been qualitatively observed by NMR.