Long-Range Ordered Lamellar Formation with Lower Molecular Weight PS-PMMA Block Copolymers: Significant Effects of Discrete Oligopeptides at the Junction
英文:
Long-Range Ordered Lamellar Formation with Lower Molecular Weight PS-PMMA Block Copolymers: Significant Effects of Discrete Oligopeptides at the Junction
We achieved the long-range ordered lamellar formation through phase separation of PS-PMMA block copolymers having low number-averaged degrees of polymerization (DPn,PS = 79 and DPn,PMMA = 107) by introduction of a discrete oligopeptide comprising several amino acids at the junction. A series of block copolymers carrying different amino acid sequence patterns were precisely synthesized, while the molecular weights of the two polymer segments were fixed. In particular, an amine-terminated polystyrene (PS) underwent an iterative amidation/deprotection with Boc-protected amino acids, followed by the reaction with an active ester-terminated poly(methyl methacrylate) (PMMA). The SAXS profiles of thus-obtained block copolymers depended on the oligopeptide structure at the junction. Consequently, the block copolymer carrying six amino acid units in the hexFFFFhex (hex: aminohexanoic acid; F: phenylalanine) sequence afforded the periodic lamella structure as supported by SAXS and TEM despite having a much lower molecular weight than the lowest value for the phase separation of unmodified PS-PMMA block copolymer predicted by Flory窶滴uggins theory. The specific phase separation behavior was further examined by DSC analyses, comparing the block copolymers with different amino acid sequences and the oligopeptide-ended PSs.
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