Microstructural analysis of poly(4-N-acrylamide-2-hydroxybenzoic acid and poly(5-N-acrylamide-2-hydroxybenzoic acid) by 13C n.m.r. spectroscopy

Abstract

The microstructural analysis of both poly(4-N-acrylamide-2-hydroxybenzoic acid) (poly(4-AHA)) and poly(5-N-acrylamide-2-hydroxybenzoic acid) (poly(5-AHA)) was carried out by one-dimensional 13C n.m.r. spectroscopy. The sensitivity of aromatic carbon signals to the stereosequences was found to depend mainly upon the carbon ability to extend into the maximum shielding zone of the neighbouring phenyl rings and carboxyl oxygens. The sensitivity of the amide carbonyl signal to the chain microstructure is influenced mainly by the γ-gauche shielding effect. Solvent-induced effects in the spectra of poly-(4-AHA) are rationalized in terms of H-bonds (for aromatic carbon signals) and bond conformation changes (for amide carbonyl carbon signal). The increase of amide carbonyl carbon signal sensitivity to the stereosequences in the spectrum of poly(5-AHA) in comparison with that of poly(4-AHA) reflects the conformation changes, induced by the transfer to more sterically crowded polyacrylate. For both poly(4-AHA) and poly(5-AHA) prepared by radical polymerization the Bernoullian statistics is required to fit the observed intensities at the triad and pentad level. © 1997 Elsevier Science Ltd.