Assignments for the 1H-NMR of alkoxy groups in syndiotactic methacrylate copolymers—I: Methyl methacrylate-methacrylic acid copolymers and methyl methacrylate-diphenylmethyl methacrylate copolymers

Unusual assignments have been observed for the ¹H-NMR of alkoxy groups in syndiotactic methyl methacrylate-methacrylic acid (MMA-MAA) copolymers and methyl methacrylate-diphenylmethyl methacrylate (MMA-DPMMA) copolymers. Thereby, the alkoxy groups OCH₃ and OCH show a degenerate pentad assignment, in as much as the two monomer units nearest to the central monomer unit exert no differentiating influence on chemical shift, in contrast to the two next-to-nearest monomer units. By the use of copolymers possessing a tendency toward alternation with respect to compositional statistics, it is possible to distinguish between a degenerate pentad and a normal triad assignment. The reason for the degenerate pentad assignment is seen in specific conformations of the pentads, leading to the elimination of the differentiating influence on chemical shift for the two monomer units nearest to the central unit.