Electro-optical properties of poly(ε-carbobenzosy-l-lysine) in organic solvents

The electric birefringence of poly(ε-carbobenzoxy-l-lysine) (PCBL) in various helicogenic organic solvents and solvent mixtures has been measured over a wide range of field strengths by application of rectangular pulses. The apparent permanent dipole moment and the optical anisotropy factor were separately determined from the field strength dependence of the steady-state birefringence. The apparent dipole moment per residue for a PCBL sample with molecular weight close to 1 × 10⁵ fell in the range of 4.7 to 5.9 D in spite of the large variation of the solvent dielectric constant. The optical anisotropy factor was appreciably small and changed its sign depending upon the solvent. The intrinsic birefringence of PCBL was found to be negative in sign on the basis of the Peterlin-Stuart theory. This was interpreted in terms of the orientation of the side chains with respect to the helical backbone. The apparent dipole moment per residue for high molecular weight PCBL samples was much smaller, indicating a considerable flexibility of the helix.