Determination of Monomer Reactivity Ratios

Copolymers of methyl methacrylate (MMA) and benzyl methacrylate (BnMA) were prepared by conventional radical copolymerization in toluene at 70 °C. The 1H nuclear magnetic resonance (NMR) spectra of these copolymers were measured in various solvents at different temperatures. The signals of the methoxy protons in the MMA units and the benzyl protons in the BnMA units showed splitting mainly because of the triad monomer sequences when the temperature was increased to 150 °C in deuterated dimethyl sulfoxide. However, the splitting was not sufficient to determine the mole ratios of the triad sequences. Therefore, multivariate analysis was applied to the 1H NMR spectra of copolymers with various chemical compositions. Principal component analysis successfully extracted information on the polymer microstructures. Partial least-squares (PLS) regression successfully predicted the mole fractions of the diad monomer sequences. Then, the fractions of the diad sequences in an unknown sample prepared in benzene at 60 °C were predicted using PLS regression to determine the monomer reactivity ratios. Thus, the monomer reactivity ratios were successfully determined from a single sample using multivariate analysis of the 1H NMR spectra of copolymers of MMA and BnMA