Effects of Poly(N‐isopropylacrylamide) (PNIPAAm) on the Conformational Change of Poly(N 5‐hydroxyalkyl glutamine) (PHAG) in PHAG‐PNIPAAm Block Copolymer with Temperature

Diblock copolymers consisting of poly(N 5 -hydroxyalkylglutamine) (PHAG) and poly(N-isopropylacrylamide) (PNIPAAm) were prepared by aminolysis with aminoalkanols of the side-chain ester of poly(γ-benzyl L-glutamate) (PLBG) as a part of PBLG-PNIPAAm block copolymers. The molecular weight ratio of the initial PBLG to the resulting PHAG was nearly 0.35. The effect of PNIPAAm on the conformational change of PHAG in PHAG-PNIPAAm block copolymers with temperature was investigated by circular dichroism. Poly[N 5 -(2-hydroxyethyl)-L-glutamine] (PHEG) and the PHEG-PNIPAAm copolymer (GNE) stayed in a randomly coiled conformation whereas poly(N 5 -(3-hydroxypropyl)-L-glutamine] (PHPG), poly(N 5 -(4-hydroxybutyl)-L-glutamine) (PHBG), PHPG-PNIPAAm copolymer (GNP), and PHBG-PNIIPAm copolymer (GNB) underwent conformational transitions with temperature.The conformational change of the PHPG block in GNP copolymer occurred from an α-helix to a random coil after the incorporatoin of PNIPAAm into the copolymer. The thermodynamic parameters of the thermally induced helix-coil transition for PHBG and PHBG-PNIIPAm in aqueous solution were calculated.