SPIN-LABEL STUDY OF IMMISCIBLE POLYMERS .2. INFLUENCE OF POLYISOPRENE ON END-LABELED POLYSTYRENE

Electron spin resonance spectra of blends of polyisoprene (PIP) and polystyrene (PS), carrying a nitroxide spin-label, show that the PIP exerts a plasticizing influence on the labelled chain-ends of PS. This effect presumably occurs at the interphase where certain of these chain-ends appear to be in a predominantly PIP environment. Treating the labelled PS as a macromolecular spin probe shows that the effective volume of an inner PS segment is ca 1.6 times greater than that of a labelled chain-end and ca 1.7 times greater than that of an inner PIP segment. Comparing the results with previously published data for spin-probed PS suggests that rotation of the chain-end label involves more than one styrene unit along the chain.