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 D-n,D-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 thusobtained 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-Huggins 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.