HIGH-RESOLUTION C-13 NUCLEAR-MAGNETIC-RESONANCE SPECTRA AND STRUCTURE OF AMORPHOUS AND CRYSTALLINE FORMS OF STEREOREGULAR POLY(METHYL METHACRYLATE)S

13C CP/MAS NMR spectra of amorphous and partly crystalline samples of isotactic (i) and syndiotactic (s) poly(methyl methacrylate) (PMMA), of a sample of partly crystalline stereocomplex PMMA, and 13C MAS NMR spectra of a toluene gel of s-PMMA were measured. The observed two bands of α-CH3 carbons in amorphous i-PMMA were assigned to trans and gauche backbone conformations; an effect of conformational structure on α-CH3 carbon resonance was observed also with s-PMMA. High-resolution13C NMR spectra of the crystalline phase in i- and s-PMMA and stereocomplex PMMA were obtained from the experimental spectra by a computer difference technique; they differ from the spectra of amorphous samples by a splitting of some bands into two components and by differences in chemical shift values. These differences are interpreted by the existence of double-helix structures in crystalline forms of stereoregular PMMA. Also the observation of equal values of the proton spin–lattice relaxation time in rotating frame T1ρH, for i- and s-components of stereocomplex PMMA is in agreement with this double-helix structure. © 1990, American Chemical Society. All rights reserved.