Conformational analysis, RIS models and single-chain properties of structurally modified polycarbonates. 1. Effect of cyclohexyl and phenyl ring substitutions

Abstract

Conformational properties of segments and chains of structurally different polycarbonates are investigated in detail. Conformational analysis and rotational isomeric state (RIS) models for some of the polycarbonates and single-chain properties of all the polycarbonates are reported here for the first time. Substitution of the methyl group on the bisphenol phenyl rings results in increased energy barriers to rotations as well as changes in positions of local minima, compared to the case without substitutions. Conformational structure about the isopropylidene linkage C_α atom is not altered by ortho methyl substitutions on the rings. Substitution by a cyclohexyl ring rigidly attached to the C_α atom restricts conformational mobility within the bisphenol unit. Rotational flexibility of the phenyl-oxygen bond is hindered by additional substitutions on the cyclohexyl ring. The carbonate group prefers the trans-trans conformation in all the polycarbonates. The energy difference between the cis-trans and trans-trans states of the carbonate group is lowered by the ortho methyl substituent on the phenyl rings. There is a reduction in <R²>, <S²>, and C_n accompanying the substitutions. The introduction of other substituents on a cyclohexyl polycarbonate results in an increase in all chain dimensions including the persistence length. Also, the cyclohexyl or trimethylcyclohexyl substituents do not significantly alter the overall average shape of the chains. Substitutions both on the phenyl rings and at the isopropylidene linkage lead to a compaction of the polymer chain, but the effect is more pronounced when due to substituents on phenyl rings.