Stereochemical configuration of polyfumarates as studied by 13C nuclear magnetic resonance spectroscopy

The 125 MHz 13C NMR spectra of some poly(dialkyl fumarates) (PDAF) and poly(dicycloalkyl fumarates) (PDCF) prepared by radical polymerization are measured in CDCl3 solution at 60°C. The multiplet resonances of the main-chain carbon atoms and the ester carbonyl carbon atoms are assigned to stereochemical triad and pentad sequences, respectively, using model compounds as well as computer simulation. From these results it is found that PDAF and PDCF exhibit essentially atactic structures with meso addition favoured over racemic addition, and that the ratio of meso to racemic content varies with different kinds of alkyl and cycloalkyl groups. The tactic sequence proportions of the polymers cannot be explained by one-parameter Bernoullian statistics, but can be successfully explained by modified Bernoullian trial.