Copolymer characterization by SEC-NMR and SEC-MALDI

Off-line SEC-NMR and SEC-MALDI measurements are performed on a series of random copolymers of methyl methacrylate, butyl acrylate, styrene and maleic anhydride. First, a method is used, consisting of fractionating the copolymer by SEC and recording both the NMR and MALDI spectra of the fractions, In a successive step, the bivariate distribution of chain sizes and composition maps are derived from a knowledge of the molar mass, weight and composition of the copolymer fractions. The compositional distribution is obtained by summation of the sections of the bivariate distribution which belong to a narrow compositional range. Secondly, a model for SEC fractionation of copolymers is developed. It permits the prediction of the composition and dispersity of each SEC fraction. Thirdly, offline SEC-MALDI measurements are performed, in order to measure dispersity experimentally for the random copolymer, The agreement between theoretical and experimental values for dispersity and for the composition of the SEC fraction (as derived from SEC-NMR measurements) is good. The predictions of the model also compare favorably with literature SEC fractionation data of a copolyester of butylene adipate and butylene sebacate.