Molecular Simulations of the Conformational Characteristics, RIS Models, and Local Intramolecular Dynamical Disparity of Substituted Polycarbonates Containing Bulky Rigid Side‐Groups

Abstract

Conformational properties of fragments and chains of substituted polycarbonates (PCs) based on cyclohexylidene, phenolphthalein, and phthalimide bisphenols are studied in detail using conformational analysis and rotational isomeric state (RIS) method. Cα substitution involving cyclohexyl groups and other rigid‐bulky cross‐planar groups does not restrict the conformational flexibility about the backbone phenyl–oxygen bond but influences to some extent the structural features of the phenyl ring relative orientations. In the cyclohexylidene PCs, phenyl, and isopropyl substituents, which are in equatorial orientations, either in meta or para positions, do not alter conformational characteristics of the bisphenyl fragment about the Cα carbon atom. The higher dihedral rotational energy barrier for backbone phenyl ring motions in phthalimide PCs, as compared to the phenolphthalein PC (PPC), shows the increased hindrance for rotations due to the presence of additional substituents (methyl, cyclohexyl, and phenyl) in the phthalmide side group. These ring rotational energy barriers are significantly higher than those in cases of conventional PC of bisphenol A. Calculated chain dimensions of substituted cyclohexylidene polycarbonate are higher than those of unsubstituted cyclohexylidene bisphenol PC. The higher rotational energy barriers among these PC fragments would lead to significant lowering of relaxation times in their condensed phase and result in relatively much higher glass transition temperatures; these observations are consistent with the experimental reported values of T g for these polymers.