Chemical Composition Distribution of Poly(methyl methacrylate)-graft-polystyrene Prepared by a Macromonomer Technique: Effect of Graft Length

Abstract

The chemical composition distributions (CCDs) of poly(methyl methacrylate)-graft-polystyrene samples prepared from the polystyrene macromonomers with different molecular weights were determined by high-performance liquid chromatography (HPLC) based on the reversed-phase and normal-phase adsorption modes. The effect of graft length on the CCDs was studied and compared to theoretical prediction. Using three ω-methacryloylpolystyrene macromonomers with molecular weights (M n = 3.0 x 10 3 , 5.8 x 10 3 , and 1.24 x 10 4 ), graft copolymers of different compositions were prepared by radical copolymerization to low conversions. These were analyzed by HPLC using a reversed-phase octadecyl-modified silica-gel column and a linear gradient of tetrahydrofuran and acetonitrile. Some samples were analyzed using also a normal-phase cyano-modified silica-gel column and a linear gradient of tetrahydrofuran and n-heptane. The chromatograms were converted to CCDs of the samples by an optimization method. Good agreements between CCDs obtained by both modes demonstrated that the effect of the molecular weight distribution on the CCD is negligible. From the CCDs obtained in the present and previous works, it was shown that the CCD is broadened as the graft length increases, in copolymer samples with a similar composition, in accordance with the theoretical prediction of Stejskal and Kratochvil.