Influence of Chain Topology on Polymer Dynamics and Crystallization. Investigation of Linear and Cyclic Poly(ε-caprolactone)s by ¹H Solid-State NMR Methods

Abstract

We report on the investigation of cyclic and comparable linear poly(ε-caprolactone)s (PεCL) with molecular weight between 50 and 80 kg/mol with regard to chain mobility in the melt and crystallinity using low-field solid-state ¹H NMR. Our results from NMR Hahn echo and more advanced multiquantum measurements demonstrate a higher segmental mobility of cyclics in the melt as compared to their linear counterparts. Rheological experiments indicate that the cyclics are less viscous than the linear analogues by about a factor of 2, confirming the NMR results. FID component analysis shows higher crystallinities of the cyclic samples by some percent under the condition of isothermal crystallization at 48 °C, suggesting that due to their enhanced overall mobility in the melt, the cyclics reach a more perfect morphology leading to higher crystallinity. We compare this finding with results from DSC measurements obtained under identical conditions and critically evaluate the applicability of polymer crystallinity determination from nonisothermal crystallization investigations by DSC. We further highlight the use of nucleating agents to investigate the particular effect of crystal growth on (nonisothermal) crystallization, separated from the influence of nucleation. These experiments indicate a faster crystal growth for cyclic samples