The effects of polydispersity on block copolymer self-assembly .

摘要

Model controlled-polydispersity poly(ethylene-alt-propylene)- b-poly(D,L-lactide) (PEP-PLA) and polystyrene- b-polyisoprene (PS-PI) diblock copolymers were synthesized by a combination of ionic and pseudo-ionic polymerization mechanisms and used to investigate the effects of increased breadth in the molecular weight distribution on block copolymer self-assembly. Small-angle x-ray scattering and rheological measurements were carried out to characterize the morphological details of these self-assembled materials as a function of their polydispersity, interaction strengths, and compositions. A number of consequences of increased breadth in the molecular weight distribution emerged; the domain spacing of the ordered structures increased, changes in morphology occurred, and the segregation strength at the order-disorder transitions changed ((chiN) ODT), particularly for asymmetric block copolymers. The change in (chiN)ODT as the polydispersity was increased was found to be dependent on the block copolymer composition, e.g., for PEP-PLA and PS-PI at asymmetric compositions, when the polydispersity was increased in the minority component, (chiN) ODT decreased, whereas when the polydispersity was increased in the majority component, (chiN)ODT increased.