Solid State CP/MAS 13C Nuclear Magnetic Resonance Spectra of Poly(4-hydroxybenzoate)s

Abstract

The high-resolution solid state 13C NMR spectra of the different crystal modifications of poly(4-hydroxybenzoate)s and their copolymers have been obtained by means of high-power proton decoupling, cross-polarization, and magic angle spinning. The resolution was sufficient in order to resolve the resonance lines of all seven differently bonded carbon atoms in the PHBA repeat unit. From the chemical shift splitting of the ortho ring carbon atoms it is deduced that, in crystalline PHBA, the torsional angle between the ester plane and the phenylene ring plane deviates from 90°. The deviation increases in the order modification II > modification III > modification I. The variable-contact-time measurements indicate that the chain packing in crystal modification I is denser than in the crystal modification II.