Conformational transformation of poly(β-phenetyl-L-aspartate) in block copolymer with polystyrene in 1,1,2,2-tetrachloroethane

Abstract

Temperature dependences of conformations of poly(β-phenethyl-L- aspartate) (PA) in block copolymer systems, in which polystyrene (PS) was attached to either N-terminus (PAn-N-PSm) or C-terminus (PSn-C-PAm) of the PA, respectively, were investigated in 1,1,2,2-tetrachloroethane (TCE) solutions by using 1H NMR spectroscopy. The block copolymers were synthesized by combination of atom transfer radical polymerization and ring-opening polymerization of N-carboxy amino acid anhydride. Whereas PA homopolymer (H-PAn, n = 68) with right-handed helical conformation started to transform to left-handed structure at 70°C, the helical-sense inversion of PA68-N-PS38 occurred at a lower temperature, 40°C. Further transformation from left-handed conformation was not observed for both polymers in the temperature range of 70°C to 110°C. On the other hand, 1H NMR spectra of PS70-C-PA170 showed coexistence of right- and left-handed helices of PA at 8.2 and 8.8 ppm at 30°C, respectively. These peaks, however, disappeared above 90°C, and a new peak at 8.5 ppm was observed. Thus, the introduction of PS chain into PA termini affected conformational stability of PA in a different way, although the transformational behaviors were not influenced by the difference of the chain length of PS segments. © 2007 The Society of Polymer Science.