QUASI-ELASTIC LIGHT-SCATTERING FROM BRANCHED POLYMERS .1. POLYVINYLACETATE AND POLYVINYLACETATE-MICROGELS PREPARED BY EMULSION POLYMERIZATION

Emulsion polymerization of vinylacetate leads to branched polymers which at high monomer conversions form microgels of the shape and size of the latex particles. Quasielastic light scattering measurements from samples in the pre-gel state give at small q2 a linear angular dependence of Dapp = G{cyrillic} q2 which resembles that of randomly branched chain molecules, where G{cyrillic} is the decay constant of the time correlation function. Extrapolation of Dapp towards zero scattering angle yields the translational diffusion constant Dz. The diffusion constant follows the molecular weight dependence Dz = 9.78 10-5 Mw-0.478. The diffusion constant of the microgels, i.e. at molecular weights Mw > 14 106, remains constant because of the finite and constant size of the latex particles. The coefficients kf and kD in the concentration dependence of the frictional and diffusion coefficients are related according to the equation kD = kf - 2A2Mw - v ̄ where A2 is the second virial coefficient and v̄ the partial specific volume of the particle. The coefficient kf is calculated from the experimentally determined quantities kD, A2 and Mw, and the result is compared with the theory by Pyun and Fixman. Accordingly the branched coils in the pre-gel state resemble soft spheres, but the microgels behave more like spheres of some rigidity. © 1979.