Morphology and Phase Transitions in Styrene-Butadiene-Styrene Triblock Copolymer Grafted with Isobutyl Substituted Polyhedral Oligomeric Silsesquioxanes (preprint)

摘要

Two symmetric triblock polystyrene-butadiene-polystyrene (SBS) copolymers with different styrene content were grafted with varying amounts of isobutyl-substituted polyhedral oligomeric silsesquioxane (POSS) molecules. The POSS octamers, R'R7Si8O12 were designed to contain a single silane functional group, R', which was used to graft onto the dangling 1,2 butadienes in the polybutadiene block and seven identical organic groups, R=isobutyl (iBu). Morphology and phase transitions of these iBu-POSS modified SBS were investigated using small angle X-ray scattering and rheological methods. It was observed that POSS with isobutyl moiety, when grafted to the polybutadiene (PB), appears to show a high affinity to stay within the PB domain; effectively, they enhance the segregation between butadiene and styrene domains. This causes a shift in the phase diagram to lower styrene content. From the rheology, we observed that values of storage modulus, G', at temperatures below the order- disorder transition increase due to the grafting of iBu-POSS. These observations lead us to conclude that the local order morphology between styrene and butadiene domains was better preserved due to the enhanced segregation forced by iBu-POSS.