2018 Volume 39 Issue 3 Pages 102-110
An ABA type block copolymer with oligoalanine and methionine chains (the degree of polymerization＝5 and 11) was successfully synthesized by the chain growth polycondensation of N-phenoxycarbonyl derivative of L-amino acid (alanine and methionine) with poly(propylene oxide) having amino groups at the terminal group as an macroinitiator. The polycondensation proceeded smoothly by heating at 60 ℃ along with the elimination of phenol and CO2 to afford block copolymers in high yield. Flexible and transparent films of block copolymers were readily fabricated by solvent-casting method on the Teflon substrates. The FT-IR measurement revealed that oligoalanine segment formed physically cross-linked network through hydrogen bond of β-sheet structure. On the other hand, oligomethionine chain formed predominantly α-helical structure. The mechanical strength of the prepared film was evaluated by a tensile test, and we found that the modulus and tensile strength increased as the degree of polymerization of the oligopeptide chain increased. β-Sheet-forming oligoalanine segment was more effective for the increment of physical property than α-helical structure. Owing to the highly solubility of block copolymer having oligomethionine chain, the mechanical strength was further improved when treated with hexamethylene diisocyanate to form the multi-block copolymer.
