SPIN-LABEL STUDY OF IMMISCIBLE POLYMERS .4. LOCATION OF CHAIN-ENDS IN BLENDS OF POLY(METHYL METHACRYLATE) AND POLY(2-ETHYLHEXYL METHACRYLATE)

The electron spin resonance (e.s.r.) spectra of nitroxide end-labelled poly(methyl methacrylate) (PMMA) were recorded over a temperature range for the pure, bulk polymer and for 1:1 (w/w) immiscible blends with poly(2-ethylhexyl methacrylate) (PEHMA) and polystyrene (PS). The changes in the e.s.r. spectra brought about by blending and varying the temperature show that chain ends tend to congregate in the interphase region. In the blends of PMMA and PEHMA the chain ends of the PMMA in the interphase are mobilized through plasticization by the rubbery PEHMA. This phenomenon was observed previously in blends of end-labelled PS with unlabelled polyisoprene. Our present results, particularly from the PMMA-PS blends, reveal that an additional enhancement of mobility of chain ends results from the accumulation of free volume in the interphase.