Crystallization and melting of unentangled poly(ε-caprolactone) cycles containing pendants

The Rouse model provides a basic framework to understand the chain dynamics of polymers, which is confirmed to be more suitable for exploring the linear dynamics of unentangled polymers. The crystalline morphology governed by chain dynamics and crystallization kinetics is expected to differ in linear and cyclic polymers. Cyclic poly(& epsilon;-caprolactone)s (c-PCLs) containing two bi-anthracenyl group pendants with molecular weights close to the critical molecular weight (M-c) were synthesized to investigate the chain dynamics based crystallization and melting behavior by DSC, POM, and in situ simultaneous small-angle X-ray scattering/wide-angle X-ray scattering (SAXS/WAXS) investigations during heating of the isothermally crystallized samples. Double endothermic peaks were observed in the DSC curves with a low heating rate of c-PCLs without entanglement after isothermal crystallization, especially for c-PCLs with M-c. The structure evolution of the crystalline structures observed from the in situ investigations during the heating and double endothermic peaks in DSC heating curves of the c-PCLs indicate the role of pendants in the chain dynamics, which leads to the reorganization of the metastable structures. Banded spherulites of c-PCL without entanglement were observed for the first time, and the uneven growth of spherulites along the radial direction may be caused by the mismatch between chain dynamics and crystallization kinetics.

Automated summary

The Rouse model is suitable for exploring the linear dynamics of unentangled polymers and provides a basic framework for understanding polymer chain dynamics. In this study, cyclic poly(& epsilon;-caprolactone)s (c-PCLs) with bi-anthracenyl group pendants were synthesized to investigate the chain dynamics and crystallization behavior. The results showed double endothermic peaks in the DSC curves of c-PCLs after isothermal crystallization, indicating the role of pendants in the reorganization of metastable structures. Banded spherulites of unentangled c-PCLs were observed for the first time, suggesting a mismatch between chain dynamics and crystallization kinetics.