Metal-sulfonated EPDM

A thermopolastic elastomer based on sulfonated-EPDM, S-EPDM, was developed in the 1970 s by Exxon and more recently by Uniroyal. Unlike the synthesis of the carboxylate ionomers described above, S-EPDM is prepared by a post-polymerization sulfonatlon reaction(28). Compared to the metal neutralized S-EPDM, the sulfonic acid derivative is not highly associated. The free acid materials possess low strengths and are less thermally stable. The metal salts of S-EPDM have properties comparable to crosslInked elastomers, but they do exhibit viscous flow at elevated temperatures. In the absence of a polar cosolvent, such as methanol, hydrocarbon solutions of the metal salts of S-EPDM are solid gels at polymer concentrations above several percent(31). With the addition of 1 to 5% alcohol the polymer solution becomes fluid with solution viscosities of the order of 10 to 100 poise. 

This paper describes (a) the synthesis of metal sulfonate-containing EPDM elastomers via sulfonation through the residual unsaturation and the neutralization of the resultant sulfonic acids, and (b) the effects of molecular weight, composition, and structure on the physical properties of the resultant ionomer. 

The composition and structure of the base EPDM and the sulfonate content of the metal sulfonate-containing EPDM exert substantial effects on the mechanical and flow properties of ionomers. The systems discussed to this point have all contained zinc sulfonate groups. In terms of melt flow the zinc cation is the cation of choice. The metal cation borne by... 

In summary, it has been shown that profound changes in the properties of EPDM can be made through the introduction of metal sulfonate groups. Relatively low sulfonate levels, approximately 20-30 meq sul-... 

Plasticization of Metal Sulfonate-Containing EPDM with Stearic Acid Derivatives... 

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. 

It is possible to add agents to metal sulfonate-containing EPDM to reduce melt viscosity and to improve melt processability. Canter and Buckley (3) were the first to preferentially plasticize metal sulfonate-... 

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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