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Further evaluation of sequences in methyl methacrylate/methacrylic acid copolymers by 1 H‐NMR in different solvents and 13 C‐NMR

1976; Wiley; Volume: 177; Issue: 8 Linguagem: Inglês

10.1002/macp.1976.021770813

0025-116X

A. Johnsen, Ernst Klesper, Toni Wirthlin,

Molecular spectroscopy and chirality

Abstract The assignment of configurational pentads‐compositional triads in the 13 C‐NMR spectra of atactic methyl methacrylate‐methacrylic acid (MMA‐MAA) copolymers is studied. Based on the known chemical shifts of the pentad‐triad sequences in syndiotactic and isotactic MMA‐MAA copolymers, as well as in atactic PMMA and atactic PMAA, chemical shift increments are derived which allow the postulation of the chemical shifts of the remaining pentad‐triad sequences. The postulated assignment of these sequences is verified by comparison of experimental 13 C‐NMR peak intensities of three different types of atactic MMA‐MAA copolymers with calculated peak intensities. Because the experimental peak intensities are composed of more than one pentad‐triad resonance which strongly overlap, and can therefore be measured only as a sum, the three MMA‐MAA copolymers are chosen to possess widely differing compositional statistics at the same P (A). The calculated peak intensities are based on the copolymerization theory for the first type copolymer, which was obtained by radical‐initiated copolymerization. For the second type copolymer, derived by half‐esterification of poly(methacrylic anhydride) with methanol, the compositional‐configurational triad peak intensities are first determined by 1 H‐NMR spectra using three different solvents. Some features of the statistics of this type of polymer analogous reaction are set forth, and the opening of the anhydride ring is found to be random. This fact allows the accurate calculation of the probabilities of the pentad‐triad sequences. For the third type copolymer, derived by hydrolysis of atactic PMMA in pyridine/water, a blocklike compositional triad distribution was found, which is—as opposed to the second type copolymer—statistically correlated with the configurational sequences. Only an approximate calculation of the probabilities of the pentad‐triad sequences was carried out. For all three types of copolymers a reasonable agreement between experimental and calculated pentad‐triad peak intensities was found.