CONFORMATIONAL ASYMMETRY IN POLY(VINYLCYCLOHEXANE) CONTAINING DIBLOCKCOPOLYMERS

Three types of compositionally symmetric and nearly monodisperse diblo ck 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 c atalytically saturated, yielding poly(vinylcyclohexane)-poly(ethylethy lene) (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 unsatu rated and saturated diblock copolymers using dynamic mechanical spectr oscopy. Changes in T(ODT) with saturation are dependent on the resulti ng 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 anticip ates the PVCH-PEE behavior but fails to account for the PEP-PVCH and P E-PVCH results. Entropic arguments based on differences in the conform ational characteristics of each block appear to be correlated with the associated variations in the segment-segment interaction parameter, c hi. These findings support earlier speculation regarding the role of c onformational asymmetry in the thermodynamics of polymer-polymer syste ms.