220‐MHz NMR spectra of acrylic monomer–2‐substituted 1,3‐diolefin alternating copolymers

Abstract

AbstractAn investigation by 220‐MHz NMR spectroscopy was carried out on the alternating copolymers of acrylic monomer with 2‐substituted 1,3‐diolefin. The chain structures were determined. The acrylic monomers used were methyl methacrylate (MMA), acrylonitrile (AN), and methacrylonitrile (MAN); isoprene (IP) and chloroprene (CLP) were the 1,3‐diolefins. In the MAN–IP alternating copolymer, the 1‐position methylene protons of IP showed an AB quartet peak, confirming the α‐1 linkage structure. Similarly, in the MMA–CLP and AN–CLP copolymers, the 1‐position methylene protons of CLP showed and AB quartet and an ABX pattern, respectively, confirming the α‐1 linkage structure in both these cases also. The α‐1 linkage structure was also revealed by the decoupling technique in the MAN–CLP alternating copolymer. The AN–IP and MMA–IP alternating copolymers also possess a bond between the α‐position of the acrylic monomer and the 1‐position of IP. The monomeric units in the alternating copolymers of acrylic monomers with 2‐substituted 1,3‐diolefins were generally linked at the α‐position of acrylic monomer and the 1‐position of 1,3‐diolefin. On the other hand, in the Diels‐Alder adducts of acrylic monomer with 2‐substituted 1,3‐diolefin, the reaction takes place between the α‐position of acrylic monomer and the 4‐position of 1,3‐diolefin.The regioselectivity of the alternating copolymers and the Diels‐Alder adducts is quite compatible with the expectations from molecular orbital theory.