NMR Study of the Chain Microstructure of P(MMA-co-MAA)
by J. R. Lyerla,Jr.
The usefulness of proton and carbon-13 NMR spectroscopy in characterizing the chain microstructure (i.e., sequence distribution and tacticity) of methyl methacrylate-methacrylic acid (MMA-MAA) copolymers has been investigated. Because the comonomers have such similar structures, assessment of chain tacticity and sequence distribution required computer simulation of spectra to circumvent the problems of resonance overlap. The computer analysis used 1H and 13C chemical shift data on homopolymers and “sterically-defined” copolymers, Bernoullian and Markovian statistics for the respective tactic and sequence distributions, and a Lorentzian lineshape program to generate a theoretical spectrum. The generating parameters that produced simulation of both the 1H and 13C spectra provided the basis for describing the triad microstructure of the copolymers. This method of characterizing the microstructure was applied to copolymers of similar composition but different preparative histories. The results indicated that free-radical polymerization in toluene yielded a heterogeneous copolymer system while free-radical polymerization in tetrahydrofuran (THF) and emulsion polymerization yielded relatively homogeneous systems.