The Order-Disorder Transition In Graft Block Copolymers

The order disorder transitions of diblock copolymers grafted to a common backbone were examined by oscillatory shear rheology and small-angle X-ray scattering. The effect of grafting density, graft molecular weight, number of grafts, and backbone dispersity were studied using poly[(styrene-alt-N-hydroxyethylmaleimide)-random-(styrene-alt-N-ethylmaleimide)]-graft-poly(4-methylcaprolactone-block-D,L-lactide) [PSHE-g-(P4MCL-PLA)] as a model graft block copolymer. At high grafting densities (25-50%), the order-disorder temperature (T-ODT) of the graft polymers was nearly identical to the analogous linear diblock. At lower grafting densities (<25%), the T-ODT was found to systematically decrease. The number of grafts did not significantly change the value of the T-ODT; however, increasing the number of grafts resulted in broad, ill-defined transitions. Backbone dispersity was found to have little impact on the T-ODT. Ordered morphologies were imaged by transmission electron microscopy. Long-range order was observed in polymers with at least 10 grafts/chain.