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) an d poly(N-isopropylacrylamide) (PNIPAAm) were prepared by aminolysis with am inoalkanols of the side-chain ester of poly (gamma -benzyl L-glutamate) (PB LG) 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 PN IPAAm on the conformational change of PHAG in PHAG-PINAPAAm block copolymer s with temperature was investigated by circular dichroism. Poly(N-5-(2-hydr oxyethyl)-L-glutamine) (PHEG) and the PHEG-PNIPAAm copolymer (GNE) stayed i n a randomly coiled conformation whereas poly(N-5-(()4-hydroxybutyl)-L-glut amine) (PHPG), PHPG-PNIPAAm copolymer (GNP), and PHBG-PNIPAm copolymer (GNB ) underwent conformational transitions with temperature. The conformational change of the PHPG block in GNP copolymer occurred fron an alpha -helix to a random coil after the incorporation of PNIPAAm into the copolymer. The t hermodynamic parameters of the thermally induced helix-coil transition for PHBG and PHBG-PNIPAAm in aqueous solution were calculated.