Sulfonated EPDM ionomer

Xie H. and Ma B., Properties of sulfonated EPDM ionomers obtained by sulfonation in the presence of phase transfer catalyst, J. Macromol. Sci. Phys., 51, 1328, 1989. 

Upaeglis A. and O Shea F.X., Thermoplastic elastomer compounds from sulfonated EPDM ionomers. Rubber Chem. TechnoL, 61, 223, 1988. 

The sulfonated EPDM ionomers were prepared by neutralizing the free acid form of the polymer in solution with the specified quaternary phosphonium hydroxide. The free acid form of the sulfonated EPDM was prepared from a commercial EPDM—Vistalon 2504 manufactured by... 

Shape memory elastomers were prepared from mixtures of a sulfonated EPDM ionomer and fatty acid salts, FAS, (ZnOleate),. Physical crosslinks in the ionomer that arise from inter-chain ionic interactions provide a permanent shape, while the crystalline low molecular weight FAS provides the means for a temporary shape. The material can be deformed above the melting point (T ) of the FAS and the new shape can be fixed by cooling the material under stress to below Tm of the FAS. Polar interactions between the ionomer and the FAS stabilize the dispersion of the FAS in the polymer and provide the continuity between the phases that allows the crystals of the FAS to provide a second network of physical crosslinks. 

Zn-SPS ionomer, 74 479 Zn sulfo-EPDM ionomers, 74 483 Zn-sulfonated polystyrene (ZnSPS) ionomer, 74 465 Zocor, 5 143... 

Sulfonated EPDMs are formulated to form a number of rubbery products including adhesives for footwear, garden hoses, and in the formation of calendered sheets. Perfluori-nated ionomers marketed as Nation (DuPont) are used for membrane applications including chemical-processing separations, spent-acid regeneration, electrochemical fuel cells, ion-selective separations, electrodialysis, and in the production of chlorine. It is also employed as a solid -state catalyst in chemical synthesis and processing. lonomers are also used in blends with other polymers. 

Sulfonated ionomers are also characterised by IR spectroscopy [75-77]. Agarwal and coworkers [76] analysed the Zn+2 salt of sulfonated EPDM. The peak at about 1200 cm 1 is due to the asymmetric stretching of the sulfonate group. The band at 1020 cm 1 is ascribed to the symmetric stretching of the -S03 group. The position and nature of the absorption band depend on the nature of the cation [76]. The band at 610-615 cm 1 is due to C-S stretching of the polymer -S03 band. 

Reference 7 reviews a number of electron microscopy studies of ionomer morphology in the period up to 1979. None of these studies makes a convincing case for the direct imaging of ionic clusters. This is because of the small size of the clusters (less than 5 nm based on scattering studies) and difficulties encountered in sample preparation. The entire problem was reexamined in 1980(21). In this study ionomers based on ethylene-methacrylic acid copolymers, sulfonated polypentenamer, sulfonated polystyrene and sulfonated ethylene-propylene-diene rubber (EPDM) were examined. The transfer theory of imaging was used to interpret the results. Solvent casting was found to produce no useful information about ionic clusters, and microtomed sections showed no distinct domain structure even in ionomers neutralized with cesium. Microtomed sections of sulfonated EPDM, however,... 

The second route to ionomers Involves modification of a preformed polymer. Sulfonation of EPDM, for example, permits the preparation of sulfonated-EPDM with a level of sulfonate groups in proportion to the amount of sulfonating agent(27). These reactions are conducted in homogeneous solutions permitting the direct neutralization of the acid functionality to the desired level. Isolation of the neutralized ionomer is effected by conventional polymer isolation techniques, such as coagulation in a nonsolvent or solvent flashing. These procedures are detailed in several patents and publications(28-31). 

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. 

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 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. 

Effect of Counterion Structure on Ionomer Properties Quaternary Phosphonium Counterions in Sulfonated EPDM... 

Blends with sulfonated EPDM zinc ionomer gave synergistic increase in tensile strength [80]. 

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). 

Sulfonation is very useful chemical modification of polymer, as it induces high polarity in the polymer changing its chemical as well as physical properties. Sulfonated polymers are also important precursors for ionomer formation [75]. There are reports of sulfonation of ethylene-propylene diene terpolymer (EPDM) [76, 77], polyarylene-ether-sulfone [78], polyaromatic ether ketone [79], polyether ether ketone (PEEK) [80], styrene-ethylene-butylene-styrene block copolymer, (SEBS) [81]. Poly [bis(3-methyl phenoxy) phosphozene] [82], Sulfonated polymers show a distinct peak at 1176 cm"1 due to stretching vibration of 0=S=0 in the -S03H group. Another peak appears at 881 cm 1 due to stretching vibration of S-OH bond. However, the position of different vibrational bands due to sulfonation depends on the nature of the cations as well as types of solvents [75, 76]. 

The ionic aggregates present in an ionomer act as physical crosslinks and drastically change the polymer properties. The blending of two ionomers enhances the compatibility via ion-ion interaction. The compatibilisation of polymer blends by specific ion-dipole and ion-ion interactions has recently received wide attention [93-96]. FT-IR spectroscopy is a powerful technique for investigating such specific interactions [97-99] in an ionic blend made from the acid form of sulfonated polystyrene and poly[(ethyl acrylate - CO (4, vinyl pyridine)]. Datta and co-workers [98] characterised blends of zinc oxide-neutralised maleated EPDM (m-EPDM) and zinc salt of an ethylene-methacrylic acid copolymer (Zn-EMA), wherein Zn-EMA content does not exceed 50% by weight. The blend behaves as an ionic thermoplastic elastomer (ITPE). Blends (Z0, Z5 and Z10) were prepared according to the following formulations [98] ... 

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. 

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