Direct detection of high mobility around chain ends of poly(methyl methacrylate) by the spin-labeling

Effects of chain ends on the dynamics of atactic poly(methyl methacrylate) (PMMA) was studied by the spin-label technique. PMMA's with well-defined molecular weights were synthesized by atom transfer radical polymerization and selectively labeled at the end or inside sites of the chain with a stable nitroxide radical. The WLF treatment demonstrated that a transition temperature, T5.0mT, at which an extreme separation width was 5.0 mT, reflected the glass transition observed at a frequency of electron spin resonance (ESR). The T5.0mT of the PMMA labeled at the chain end (T5.0mT,e) was ca. 8 K lower than that of the PMMA labeled at the inside sites (T5.0mT,i). From the comparison of some polymers, the difference between the T5.0mT,i and T5.0mT,e of a rigid polymer was found to be larger than that of a flexible polymer. The T5.0mT,i and T5.0mT,e decreased with a decrease in the molecular weight as well as a glass transition temperature determined by calorimetric measurements. This result supports that the T5...