Reversing‐pulse electric birefringence of poly(γ‐benzyl‐L‐glutamate). I. Transient behavior of fractionated samples in the low electric field region

Abstract

AbstractReversing‐pulse electric birefringence (RPEB) was measured for the first time for four fractionated poly(γ‐benzyl‐L‐glutamate), [Glu(OBzl)]n, samples in N,N‐dimethylformamide (DMF) at 20°C and at 535 nm. The RPEB signal showed a deep minimum for each sample on reversal of an applied electric field. The profiles of the reverse‐transient signal were analyzed by taking into account the polydispersity for the continuous distribution of molecular lengths. The best set of three quantities (lw, lw/ln, (βw)2/2γw), which determine a signal profile, was evaluated for each sample. By combining the experimental data of intrinsic viscosity and RPEB, the diameter of a cylinder, which is assumed for the [Glu(OBzl)]n helix, was found to be 17 Å. The value (βw)2/2γw, which is related to the ratio of weight‐average permanent dipole moment μw, and electric polarizability anisotropy Δαw, was found to be in the range of 20–45. This indicates that the former contributes predominantly to electric field orientation, but the latter also should not be ignored. With the three parameters from the reverse portion, the rise and decay curves were regenerated theoretically in excellent agreement with experimental signals.