Development Of High Mooney Viscosity, Homogeneous Long Chain Branched EPDM

EPDM grades for sponge extrusions for automotive weather strip are highly specialized, and have reached a high degree of advancement to meet the increasing demands for automotive sealing.  The collapse resistance of a sponge profile is governed by the polymer through a combination of its molecular weight and branching.  Historically, coupled branching has been introduced via in-reactor or post-reactor coupling chemistry to increase the melt elasticity of the polymer. Through advancements in catalyst and process technology, a new EPDM has been developed to meet the performance rheology demanded for optimum sealing and processing performance.   Enabled by the homogeneous incorporation of long chain branching (hLCB), the rheological response of an EPDM can be systematically tailored. At high degrees of hLCB, the melt elasticity of the polymer is greatly improved while eliminating issues with gel formation.   As a result, high collapse resistance can be achieved in rubber compounds to obtain the closed-cell structure demanded for premium sponge profiles.  In addition to high melt elasticity, the high shear flow of the polymer is also improved to facilitate dispersion, mixing and extrusion. This paper will review the historical and technological advancements that have enabled this new development.