Complex Polymer Mixture Analysis by On-Line LC(GPC)-NMR

摘要

We have recently explored the application of on-lien LC-NMR and GPC-NMR methods to quantitatively determine polymer compositions in a mixture or as a function of molecular weight distribution. Such a powerful tool has not been fully exploited for polymer characterization due to strong solvent (eluent) signals in NMR. In this study, we have successfully applied the bipolar gradient pulses stimulated echo sequence (BPPSTE) to suppress solvent and small molecule impurity signals, based on the different diffusion property between polymers and small eluent molecules. The lower the molecular weight of the species, the higher the diffusion coefficient, hence the faster the signal decays with BPPSTE NMR. Using a reverse-phase C-18 column and acetonitrile/THF solvent gradient, we have examined poly(methyl methacrylate) (pMMA), polystyrene, poly(butyl acrylate) (pBA) and polybutadiene polymer mixtures and have completely determined the structure and blockiness (monomer sequences) of various copolymers in the mixture. With on-line GPC-NMR, we were able to determine the complete composition and blockiness of pMMA, pBA and polystyrene mixtures at various molecular weights. The GPC-NMR method proved to be an excellent approach to examine the chemical composition and microstructure of polymers as a function of the distribution of molecular weight.