Polymer NMR spectroscopy. VI. Methyl methacrylate–styrene and methyl methacrylate–α‐methylstyrene copolymers

TLDR

The NMR spectra of methyl methacrylate–styrene and methyl methacrylate–α‑methylstyrene copolymers show an unexpected multiplicity in the 6.4–7.8 τ region, attributed to magnetic shielding by styrene units. The study compares statistical monomer sequence probabilities with methoxyl peak areas to determine how shielding of methoxyl protons depends on nearest‑neighbor styrene units and their stereochemical configuration relative to methyl methacrylate. The analysis explains the spectra and partially describes the stereochemical configuration of the copolymers, and the NMR method is useful for analyzing other block and graft copolymers.

Abstract

Abstract The NMR spectra of methyl methacrylate–styrene and methyl methacrylate–α‐methylstyrene copolymers exhibit, among other features of interest, an unexpected multiplicity in the 6.4–7.8 τ region, characteristic of methoxyl protons. This multiplicity is believed due to magnetic shielding by styrene units. By comparing the results of a statistical analysis of monomer sequence probabilities with the relative areas of the methoxyl peaks, it is shown that the degree of shielding of the methoxyl protons is dependent not only upon the presence of styrene units as nearest neighbors along the chain but also upon their stereochemical configuration with respect to the methyl methacrylate units. By means of reasonable assumptions it is possible to explain the copolymer spectra and to give a partial description of the stereochemical configuration of the methyl methacrylate–styrene copolymers. The NMR method should be valuable in the analysis of other copolymers, particularly block and graft copolymers.