Stereochemical approach to understanding the role of segmental motion and specific breaks in the flexibility of high molecular weight poly(n-alkyl isocyanates)

Poly(n-alkyl isocyanates), which form extended helical conformations, have been the subject of a large literature concerned with their solution properties. This work shows the scaling characteristics of a rod for the relationship of molecular weight to radius of gyration, viscosity,² and dipole moment³ at degrees of polymerization up to about 1,000 with gradual decay to coil-like properties as molecular weight increases. This is characteristic of worm-like chains and leads to the inevitable question about the structural source of the accumulated flexibility. Differing viewpoints have assigned the flexibility either to smooth bending of the stiff helix or to changes in chain direction associated with helix reversals. A stereochemical approach is taken to attempt to answer these conformational questions, which relate also to the liquid crystal forming characteristics of these polymers.