Synthesis and Rheological Characterization of Branched Versus Linear Solution Styrene-Butadiene Rubber

By mediating the reactivity of the initiator/modifier system toward metallation of the polymer backbone, we have developed synthetic strategies that effectively control the relative level of branching and polydispersity in SSBR. This development has allowed for the optimization of both the microstructure and macrostructure of solution elastomers to meet the demands of a given application. In this study, we have taken the approach of controlling the polymer macrostructure by adjusting our initiator/modifier system so as to mediate the propensity for backbone metallation to occur. Understanding it is from the metallated sites along the polymer backbone that branches tend to propagate, we have demonstrated the ability to produce varying degrees of branching. Several synthetic strategies were employed in order to impose control over the levels of branching in solution SBRs. The macrostructure is the independent variable in this study and subtle differences can have profound effects on the rheology and, thus, mixing, extruding and even physical properties of the resultant compound. Polymer samples were characterized by light scattering and several rheological tests to determine the relative levels of branching in order to verify the proposed synthetic mechanisms that underlie branching control.