Strain State of Poly(N-isopropylacrylamide) in Polystyrene-b-Poly(N-isopropylacrylamide) Block Copolymers and Binary Blends with Polystyrene

摘要

Three diblock copolymers of polystyrene-b-poly(N-isopropylacrylamide) (PS-b-PNIPAM) were prepared by reversi-ble addition-fragmentation chain transfer technique (RAFT) withcompositions f_(ps) = 0. 84, f_(Ps) =0. 29, and f_(Ps) = 0. 33. Block copoly- mers rich in PNIPAM were blended with polystyrene and its mor- phological effects were studied. The morphology of thin filrms was induced by acetone vapor and determined in the dried state by means of TEM. Copolymers with f_(ps)= 0.84 and f_(ps) = 0.29 form hexagonally packed cylinder (HPC) morphologies while thatwith f_(Ps) = 0. 33 corresponds to a lamellar structure. Inalmost all cases where PNIPAM constitutes the continuous phase, a con- traction of the PNIPAM blocks with respect to their averageunperturbed dimension was observed, contrary to what one expects from the physics of self-assembly of block copolymers. In contrast, for HPC morphology where PNIPAM is confined in a PS matrix, both blocksare highly extended.