Segmental Dynamics and Self-Concentration around Chain Ends in Miscible Blend of Poly(cyclohexyl methacrylate) and Poly(cyclohexyl acrylate) As Studied by the Spin-Label Technique

Abstract

Local segmental dynamics of poly(cyclohexyl methacrylate) (PCHMA) and poly(cyclohexyl acrylate) (PCHA) in their miscible blend was determined by the spin-label technique. The PCHMA and PCHA chains were labeled with nitroxide radicals at chain ends or inside sites, respectively. The temperature-dependent electron spin resonance (ESR) spectra of the spin-labels selectively reflected the segmental dynamics around the labeled sites. Specific chain dynamics of the PCHMA and PCHA components in the blend was separately detected even though a single glass transition was observed in calorimetric measurements.The Lodge−McLeish model (L−M model) on the basis of the self-concentration effect in the blend predicted well the individual chain dynamics detected by the spin-labeling. This agreement implies that the local length scale to influence the dynamics is comparable to the Kuhn length, lk. The chain ends of the PCHA and PCHMA in the homopolymer bulk had higher mobility than those of the inside sites due to flexibility around chain ends. The PCHMA chain end had higher mobility than that of inside segments in the blend with any compositions. On the other hand, the mobility of the PCHA chain end was lower than that of the inside in the blend when the weight fraction of the PCHA was smaller than ca. 0.5. These experimental results were described well by the L−M model with the lower self-concentration around chain ends. The lower self-concentration around chain ends is considered to be caused by the discontinuity of repeat units at chain ends.