Light scattering behaviour of low-molecular-weight polymers in mixed solvents with very high selective sorption

Abstract

Some low-molecular-weight polymers (poly(butyl methacrylate), nylon 6, nylon 12) in the solvent system m-cresol/ n-heptane, with effective refractive index increments ( ∂n/ ∂c) μ in the range 0.34−0.81 ml/g, have been studied by light scattering. These extremely large values, measured by differential refractometry of solutions in the state of dialysis equilibrium, are mainly due to very great selective sorption of one solvent component ( m-cresol) on the polymers studied. The effect inherent to these systems, viz. that of the free solvent composition change, has been discussed and exemplified by the light scattering behaviour of solutions of oligomers of butyl methacrylate. The light scattering anomalies observed with solutions of some nylons in m-cresol/ n-heptane have been interpreted as due to interaction of polymer end-groups. It has been demonstrated that the determination of M w of the order of 10 3 by light scattering in systems with large ( ∂n/ ∂c) μ values, i.e. with large scattering power, is possible with good accuracy.