MOLECULAR MECHANISMS FOR THE OPTICAL ACTIVITIES OF POLYISOCYANATES INDUCED BY INTRAMOLECULAR CHIRAL PERTURBATIONS

Molecular mechanisms were proposed to account for extraordinary optica l activities of polyisocyanates containing chiral moieties (chiral mon omer or initiator fragment) reported by Green et al. and by Okamoto et al., where the polyisocyanate molecule was modeled by a helical chain consisting of an alternating sequence of right-handed and left-handed helices with helix reversals in between. Theoretical predictions base d on this model were consistent with remarkable dependence of optical rotation on monomer composition for random copolyisocyanates of chiral and achiral monomers and enantiomorphous copolymers and chain length dependence of optical rotation for achiral polyisocyanates with a chir al initiator fragment on the chain end. The helix reversal was shown t o be the key factor for all the cases and more frequent for aromatic s idechain polymer poly(m-methyl phenyl isocyanate) than for aliphatic s ide chain polymers such as poly(butyl and hexyl isocyanate)s.