New highly-crosslinked TPES based on VNB-EPDM with improved compression set
Maria D. Ellul, Advanced Elastomer Systems, L.P., USA and P.S. Ravishankar, ExxonMobil Chemical Co., USA
5-vinyl-2-norbornene EPDM, (VNB-EPDM) is more efficient than 5-ethylidene-2-norbornene, (ENB-EPDM) in peroxide crosslinking, producing high cure state at low concentrations of VNB and peroxide. Recently a process for incorporating 5-vinyl-2-norbornene, (VNB), diene termonomer in the EPDM backbone was developed, resulting in a polymer with a high degree of long chain branching by Ziegler polymerization of the VNB pendent double bond and yet free of gel. For TPVs made by dynamic vulcanization of EPDM-polypropylene, it is advantageous to use lower peroxide levels to produce highly-crosslinked TPVs, in order to mitigate the undesirable degradation of the polypropylene. Through the use of these new VNB-EPDMs only a low level of VNB termonomer is necessary (<3 wt%) to produce TPVs with lower levels of peroxide and a high degree of cure. The resulting materials have improved elasticity resulting in up to 50% lower compression and tension set values than conventional phenolic resin cured TPVs. These new peroxide-cured TPVs based on VNB-EPDM have other useful attributes that include, lighter color, low moisture uptake and improved chemical resistance.