Multivariate analysis of 13C NMR spectra to extract information about monomer sequences in poly(methyl methacrylate-co-benzyl methacrylate)s prepared by various polymer reactions

Abstract

The 13C NMR spectra of atactic copolymers of methyl methacrylate (MMA) and benzyl methacrylate (BnMA) show complicated resonance patterns due to variations in their configurational sequences and monomer sequences in the macromolecular chains. Principal component analysis (PCA) was found to be useful for extracting information regarding the chemical composition and monomer sequence from the complicated resonances of the copolymers. To assess the feasibility for monomer sequence analysis, a PCA approach was applied to the spectra of MMA-BnMA copolymers prepared by partial modification of atactic poly(benzyl methacrylate) through catalytic hydrogenolysis, acidic debenzylation, saponification, and transesterification and by two-step esterification of atactic poly(methacrylic acid) (PMAa). The analysis clearly showed the formation of highly blocky copolymers via hydrogenolysis, as well as the formation of copolymers with a somewhat alternating tendency via acidic debenzylation, saponification, and transesterification in the late processes of the reactions. The copolymers formed in early processes of these reactions were essentially random sequences. The analysis also revealed that the copolymer prepared through partial methylation of PMAa with diazomethane was a random copolymer, while the copolymer prepared through partial benzylation of PMAa with benzyl bromide was a blocky copolymer. MMA-BnMA copolymers with various monomer sequences (blocky, random, alternating tendency) were prepared by partial modifications of atactic poly(BnMA) or by direct copolymerization of MMA and BnMA. 13C NMR spectra of the copolymers were subjected to principal component analysis, one of the standard procedures of multivariate analysis. The analysis showed clearly the formation of highly blocky copolymers by hydrogenolysis as well as the formation of copolymers with somewhat alternating tendency by the acidic debenzylation, saponification, and transesterification at late processes of the reactions.