Influence of Cross-Link Structure on Viscoelasticity of Polybutadiene Latex Films

Dynamic viscoelastic properties of the casted films of polybutadiene latex, in which gel content was controlled by i) terminating the reaction at a certain conversion, or ii) increasing the amount of chain transfer agent were measured to study the crosslink structure. The glass transition temperature (Tg) and tan δ peak at Tg were independent of the gel content, i. e., the cross-linking degree, but dependent on the molecular weight of main chains. Tg of the samples prepared by ii) was slightly higher than that of the samples by i), which might be ascribed to the difference of mobility of local chains. At a higher temperature (0°C), |E*| and tan δ were dependent on both the gel content and the amount of chain transfer agent. Because time scale of samples were in the rubbery stage to flow region at 0°C, viscoelastic properties were strongly influenced by the molecular weight of sol-like portions, which exist at the boundary between the microgel particles.