NUCLEAR MAGNETIC RESONANCE STUDIES ON MICROSTRUCTURE OF ETHYLENE COPOLYMERS .3. SOLVENT EFFECTS ON PROTON RESONANCE SPECTRA OF ETHYLENE-VINYL ACETATE COPOLYMERS

Effects of solvent on the proton nmr spectra of ethylene-vinyl acetate (E-VA) copolymers have been investigated. In solutions of benzene and alkylbenzenes the solvent molecules selectively associate with the acetate methyl groups of E-VA dyads. The heats and entropies of complex formation were obtained by analyzing the temperature dependence of the observed spectra. It was found that presence of polar substituent in the aromatic solvent molecules (e.g., halobenzenes and pyridine) precludes the formation of polymer-solvent complex. Moreover, these complexes seem to have a steric dependence since bulky alkylbenzenes impede their formation. For E-VA copolymers containing more than 62.5 mol % of ethylene, the methylene protons of the alkanelike sequences give rise to two resonance peaks in aromatic solution spectra. These peaks can be assigned to the methylene groups of the two types of intramolecular structure, “polymeric” and “monomeric,” similar to those observed in the spectra of oligomeric polyethylene. The “polymeric” structure probably arises from intramolecular chain folding. © 1969, American Chemical Society. All rights reserved.