Block copolymer molecular weight by GPC



Molecular weights of narrow distribution styrene–butadiene block copolymers were determined from combined GPC–intrinsic viscosity data using the universal calibration principle and from GPC data alone using the assumption of weighted average of log molecular weights suggested by Runyon et al. The results indicate that, experimentally for block copolymers in good GPC solvents, the simpler second method is more precise despite the objection on theoretical grounds raised by Ho-Duc and Prud'homme. The calibration curves of polystyrene and polybutadiene in THF were found to be parallel, and the ratio for the two molecular weights at equal elution volume was found to be 1.75, differing from the 2.0 value reported earlier.