CONFORMATIONAL ASYMMETRY IN POLY(VINYLCYCLOHEXANE) CONTAINING DIBLOCK COPOLYMERS

Three types of compositionally symmetric and nearly monodisperse diblock copolymers, poly(1,2-butadiene)-poly(styrene) (1,2-PB-PS), poly(cis-1,4-isoprene)-poly(styrene) (1,4-PI-PS), and poly(1,4-butadiene)-poly(styrene) (1,4-PB-PS), were anionically synthesized and subsequently catalytically saturated, yielding poly(vinylcyclohexane)-poly(ethylethylene) (PVCH-PEE), poly(ethylenepropylene)-poly(vinylcyclohexane) (PEP-PVCH), and poly(ethylene)-poly(vinylcyclohexane) (PE-PVCH). The order-disorder transition temperature, T(ODT), was determined for the unsaturated and saturated diblock copolymers using dynamic mechanical spectroscopy. Changes in T(ODT) with saturation are dependent on the resulting polyolefin microstructure. PVCH-PEE has a much lower T(ODT), while PEP-PVCH and PE-PVCH display higher ones, relative to the unsaturated precursor materials. Group contribution analysis qualitatively anticipates the PVCH-PEE behavior but fails to account for the PEP-PVCH and PE-PVCH results. Entropic arguments based on differences in the conformational characteristics of each block appear to be correlated with the associated variations in the segment-segment interaction parameter, chi. These findings support earlier speculation regarding the role of conformational asymmetry in the thermodynamics of polymer-polymer systems.