Helix–helix transition of poly(β-phenylpropyl l-aspartate) embedded in stable helical poly(γ-phenylethyl glutamate) matrix

We studied the helix–helix transition of poly(β-phenylpropyl l-aspartate) (3PLA) embedded in a right-handed α-helical (αR) poly(γ-phenylethyl l-glutamate) (2PLG) or left-handed α-helical poly(γ-phenylethyl d-glutamate) (2PDG) matrix. Binary mixtures were prepared with 3PLA:2PLG (2PDG) mole fractions of 9:1 to 1:9. In all these mixtures, the 3PLA molecule exhibited helical sense inversion even if dispersed or isolated into the hard-rod matrix, and the inversion rate of the embedded 3PLA molecule was relatively higher than that of the pure system. Thus, it was concluded that the transition occurs in only a limited space and more easily for the isolated molecule. Further, the 3PLA molecule recognized the chiral environment produced by the surrounding polymers. For 3PLA surrounded by a 2PDG matrix, the helix–helix transition temperature was lower and the transition rate on cooling was slower than those for 3PLA surrounded by a 2PLG matrix. This is reasonable since the left-handed matrix helps right-handed to left-handed helical inversion.