Determination of molecular dimensions of linear polyethylene by light scattering

The molecular dimensions of linear polyethylene published in the literature were reevaluated in order to discuss the radii of gyration RG and their dependence on molar mass, M. The relationships RG=bMa and the exponents a of this equation in comparison with the unperturbed dimensions of linear polyethylene obtained from viscometric measurements allowed the discussion of the reliability of the data and the reasons for deviations. The exponent a determined by light scattering for linear polyethylene in good solvent, tetraline, showed molecular dissolution, whereas in 1-chloronaphthalene and trichlorobenzene, the exponent a is lower than expected for good solvents. Microgels and aggregates of molecules affect the exponents. Radii of gyration measured directly by light scattering at fractions of linear polyethylene in the theta solvent, diphenylmethane, indicate incomplete molecular dissolution and the presence of branched structures.