The Order–Disorder Transition in Graft Block Copolymers

Abstract

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 (TODT) of the graft polymers was nearly identical to the analogous linear diblock. At lower grafting densities (<25%), the TODT was found to systematically decrease. The number of grafts did not significantly change the value of the TODT; however, increasing the number of grafts resulted in broad, ill-defined transitions. Backbone dispersity was found to have little impact on the TODT. Ordered morphologies were imaged by transmission electron microscopy. Long-range order was observe...