Effect of Gel Content on Polymer Diffusion in Poly(vinyl acetate-co-dibutyl maleate) Latex Films

We used energy transfer experiments to examine the rates of polymer diffusion in latex films of two P(VAc−DBM) copolymer samples: one of nominal M w = 250 000 (by GPC, M 250K ) and the other, the high- M sample, with a substantial (50%) gel content. An important feature of this sample is that its sol fraction had a similar molecular weight distribution (similar GPC curves) to that of the M 250K sample. Films of both samples exhibited the viscoelastic response at high frequencies expected for entangled polymers. At low frequencies, the G ‘ and G ‘ ‘ values for the high- M sample were comparable in magnitude over a wide range of frequencies and were proportional to ω 0.5 . This type of behavior is often seen as a signature of a critical gel but appears here for a mixture of gel and randomly branched polymer. Our most important finding is that the rates of intercellular polymer diffusion were very similar in latex films of the two polymers. This result indicates that the diffusion rate depends primarily on the molecular weight and degree of branching of the diffusing species and is much less sensitive to the cross-linked nature of the matrix present in one of the samples.