Ab Initio Calculations of Possible γ-Gauche Effects in the (13)C-NMR for Methine and Carbonyl Carbons in Precise Polyethylene Acrylic Acid Copolymers

The impacts of local polymer chain conformations on the methine and carbonyl (13)C-NMR chemical shifts for polyethylene acrylic acid p(E-AA) copolymers were predicted using ab initio methods. Using small molecular cluster models, the magnitude and sign of the γ-gauche torsional angle effect, along with the impact of local tetrahedral structure distortions near the carbonyl group, on the (13)C-NMR chemical shifts were determined. These (13)C-NMR chemical shift variations were compared to the experimental trends observed for precise p(E-AA) copolymers as a function acid group spacing and degree of zinc-neutralization in the corresponding p(E-AA) ionomers. These ab initio calculations address the future ability of (13)C-NMR chemical shift variations to provide information about the local chain conformations in p(E-AA) copolymer materials.