Auto- and Induced Stereoregulation of Polyisocyanides

Abstract

Polyisocyanides, $\matrix{ {({\rm{ - C - }})} \cr {||{\rm{n,}}} \cr {{\rm{N - R}}} \cr }$ represent a class of polymers with unique primary structure that sets them apart from conventional polymers. Their polymeric properties in several ways are unique in kind or degree, and their exploration has already, and further promises, to broaden our experiences and understanding of macromolecular chemistry and physics. These are the subjects of some recent reviews (1–5). Poly(α-phenylethyl isocyanide), α-PPEI, is the progenitor member of the polymer class, being the first and most characterized of the few currently known soluble polyisocyanides of high molecular weight. It assumes a rigid-rod conformation, and it yields liquid crystals in solution. Most polyisocyanides are strongly aggregated solids and are insoluble in solvents other than strong acids, wherein they are protonated and show time-dependent viscosity changes. This phenomenon has led to a new viscosity concept of isoviscosity and isohydrodynamic volume (6), which has recently received some independent support (7,8). Polyisocyanides form racemic mixtures of complete stereoregular helices, and give evidence of dipole coupling of the vicinal imine groups. Hence, polyisocyanides are proposed as models of fixed dimensional coordinates for future investigation of optical, electrical and solution thermodynamic properties.