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Stress birefringence of several polymers swollen in various solvents was experimentally investigated. Gels of polystyrene (PS), natural rubber (NR), polydimethylsiloxane (PDMS), cyanoethylacetylcellulose (CEAC), and cyanoethyltritylcellulose (CETC) were studied over a wide range of degrees of swelling from dilute solutions to concentrated gels. In all systems where the increment of polymer–solvent index of refraction dn/dcdiffers from zero the form effect in stress birefringence is observed to be proportional to (dn/dc)2in accordance with the theory. The dependence of stress birefringence on the concentration of a polymer allows us to determine the relative roles of macro- and microform anisotropy in the total stress birefringence. For rigid chains of cellulose esters at all concentrations form birefringence appears to be a microform effect. For flexible chain molecules of synthetic polymers, the microform effect plays the principal part at high concentrations. According to theoretical predictions the magnitude of the microform effect for cellulose derivatives is many times greater than for flexible polymers. In both cases the form effect is caused neither by micelles nor by macroheterogeneities in gels, but is molecular in nature. Its magnitude depends on the segmental mass of the molecular chain. The use of the microform effect theory with experimental data obtained on stress birefringence of gels permits the determination of the masses of molecular segments Msfor all the polymers investigated. Values Msthus obtained agree with segmental dimensions determined by viscometry and light-scattering methods.

The flow and electric birefringence of a number of poly-?-benzyl-l-glutamate (PBLG) fractions in dichloroethane and m-cresol have been studied. Molecular weights (0.4–3.4 × 105) of the fractions are determined from measurements of diffusion and sedimentation of solutions. The hydrodynamic, optical, and electrical data obtained are used for quantitative evaluation of molecular conformation and flexibility. From the experimental dependence of molecular optical anisotropy on molecular weight, an apparent persistence length a= 1200 A. is calculated for the PBLG chain. This value is obtained by using both the intrinsic anisotropy of molecules and their microform anisotropy. A similar value, a= 1100 A., is also obtained from the dependence of diffusion and sedimentation coefficients on molecular weight. The value a= 700 A. determined from the dependence of dipole moment upon molecular weight appears to be considerably lower. This means that orientation processes of polar PBLG molecules in mechanical and electrical fields should not be considered identical and that a marked difference exists in the correlation of molecular chain segments with the phenomena of flow and electrical birefringence.