The important influence of crystalline structure on the properties of polymer materials highlights the significance of understanding polymer crystallization, but crystallization remains one of the major unsolved problems in polymer science. The long chains of polymers lead to a variety of topologies including entanglements, tie molecules and end groups that are key to understanding the problem. The chain ends with high degree of freedom play a significant role. To eliminate the entanglement effects, poly(ε-caprolactone)s (PCLs) with entanglement molecular weight were synthesized and modified with end groups (including phenyl, naphthyl and anthracenyl), and the effects of end groups on the crystallization and melting behaviors of PCLs were analyzed. Thermal effects and structural evolutions during crystallization and melting were probed using DSC, POM, and simultaneous SAXS/WAXS. The results showed that the end groups decreased the spherulite growth rate and increased the half-time of crystallization, showing an inhibitory effect on crystallization. The two SAXS peaks with a q ratio of 1:2 appearing in the heating correspond to a multiplied long period, indicating a transition from a metastable folded-chain structure to a more stable extended-chain structure. Our results demonstrate that the dynamics of polymer chains can be regulated by end groups, thereby controlling the crystallization kinetics and crystalline structure.

Effects of tails on crystallization and melting behaviors of unentangled poly(ε-caprolactone)s

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