SILANE-TERMINATED LIQUID POLY(BUTADIENES) IN TREAD FORMULATIONS: A MECHANISTIC STUDY

Abstract

ABSTRACT Liquid poly(butadienes) are materials that exhibit flow properties as their molecular weights are at or below that for significant chain entanglement. When applied to tire compound formulation in additive amounts, these low-molecular-weight oligomers are compatible with the elastomeric phase and can influence viscoelastic behavior. The present article will catalogue the history of the use of liquid poly(butadiene) materials in tire compounding, linking their varied application to the evolution of structure–property relationships as a function of microstructure changes. The result of this evolution is the commercialization of functionalized liquid polybutadienes, specifically silane-terminated grades designed for silica-filled systems. It has been found that these materials are not replacements for the typical silane coupling agents ubiquitously used in silica formulating but are rather synergistic with the established technology. The application of silane-terminated liquid poly(butadienes) can both improve traction indicators and limit the negative hysteresis effect commonly associated with the use of liquid poly(butadiene) resins. The mechanism behind the specific changes in viscoelastic and mechanical properties attributed to the addition of silane-terminated liquid poly(butadienes) is explored. It is found that the terminal silane function of the liquid poly(butadienes) may both interact with the silane coupling agent–modified surface of the dispersed silica particles and be available to condense with each other, forming a higher-molecular-weight structure that may effectively increase the apparent crosslink density and therefore bound rubber as an interpenetrating network that extends well into the elastomer phase.