Full copolymer characterization by SEC-NMR combined with SEC-MALDI.

Measurements on a series of random copolymers with units of
methylmethacrylate, butylacrylate, styrene and maleic-anhydride are
performed. A method is used which consists in fractionating the copolymer
by size exclusion chromatography (SEC), collecting 30-40 fractions and
then recording both the NMR and MALDI spectra of the fractions. In a
successive step. bivariate distribution of chain sizes and composition
maps are derived from 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. A model for SEC fractionation of copolymers is
developed. It allows to predict the composition and D(x) of the SEC
fraction (D(x) is the ratio between the number-average and the weight-
average molar mass, x is the fraction number). Offline SEC-MALDI
measurements are performed, in order to measure experimentally D(x) for
the random copolymer. The agreement between theoretical and experimental
values for D(x) and for the composition of the SEC fraction (as derived
from SEC-NMR measurements) is good. The predictions of the model were also
compared with literature data for SEC fractionation of a copolyester with
units of butileneadipate and butilenesebacate. The agreement between
theoretical and experimental values is more than satisfactory. (C) 2002
Published by Elsevier Science Ltd