Nuclear magnetic resonance study of polyisoprene/poly(vinylethylene) miscible blends

In accord with their thermodynamic miscibility, blends of 1,4-polyisoprene and poly(vinylethylene) exhibit a single glass transition. In compositions with a relative abundance of poly(vinylethylene) that is very high in 1,2-microstructure, the glass transition, as observed in calorimetry, thermal expansivity measurements, and dynamic mechanical spectra, is extremely broad. exp 1 H NMR results are presented, which corroborate the intimate nature of the mixing in this system, notwithstanding the breadth of the glass transition. Solid-state exp 13 C NMR measurements indicate that molecular motions of the components have different temperature dependencies. Despite the morphological homogeneity and thus equivalence in free volumes, carbons on the respective components exhibit distinct "glass transitions". It is this phenomenon that underlies the broad glass transitions observed by conventional methods. Such breadth, or in principle even distinct glass transition temperatures, is not inconsistent with thermodynamic miscibility. Spectra, Graphs. 34 ref.--AA