Stearates metal sulfonate EPDM

Metal sulfonate-containing ethylene-propylene-diolefin ter-polymers (EPDM) were plasticized with stearic acid and derivatives for the reduction of the melt viscosities of these ionomers through interaction with the very strong ionic associations. Substantial improvements in melt flow were achieved with stearic acid and the zinc, lead, and ammonium stearates, while other metal stearates were ineffective. Zinc stearate and lead stearate not only markedly improved melt flow but, remarkably, also enhanced the mechanical properties of the plasticized systems. These unique additives were fully compatible with the EPDM ionomers and provided thermoelastic systems with excellent physical properties and ready processability. 

This chapter describes the effects of various stearates on the rheological, mechanical, and chemical properties of metal sulfonate-containing EPDM s. 

It was noted earlied that the incorporation of metal sulfonate groups into EPDM resulted in enhanced water sensitivity. The response of the ionomer to water pick-up was a function of the metal cation borne by the sulfonate group (I). The incorporation of zinc stearate plasticizer into EPDM ionomers resulted in marked reductions in water absorption, and this is illustrated in Figure 7. In the absence of zinc stearate water absorptions of 30-80% were obtained for most cations while the lead and zinc cations absorbed about 10%. Zinc stearate markedly reduced water absorption for all metal cations. However, the zinc and lead cations yielded the lowest water absorptions. 

EPDM-Derived Ionomers. Another type of ionomer containing sulfonate, as opposed to carboxyl anions, has been obtained by sulfonating ethylene—propjlene—diene (EPDM) mbbers (59,60). Due to the strength of the cross-link, these polymers are not inherently melt-processible, but the addition of other metal salts such as zinc stearate introduces thermoplastic behavior (61,62). These interesting polymers are classified as thermoplastic elastomers (see ELASTOLffiRS,SYNTHETIC-THERMOPLASTICELASTOLffiRS). 

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