Plasticized ionomer systems

Even less is known about ionomer/plasticizer interactions on a molecular level. A variety of scattering and spectroscopic techniques that can probe this level have been mentioned, but they have been applied primarily to the specific case of water in ionomers, and in particular to hjdrated perfluorinated ionomers. At the least, these studies demonstrate the powerful potential of the techniques to contribute to a more complete understanding of structure-property relationships in plasticizer/ionomer systems. For e.xample, to return to the question of the effect of nonpolar plasticizers on the ionic domains how can the decrease in the ionic transition temperature be reconciled with the apparently minimal effect on the SAXS ionomer peaks and with the ESR studies that indicate (not surprisingly) tiiat these plasticizers have essentially no influence on the local structure of the ions Is it due to their association with the hydrocai bon component of the large aggregates or clusters Or if these entities do not exist, as some researchers postulate, what is the interaction between the nonpolar plasticizer, the hydrocarbon component and the ionic domains These questions are, of course, intimately related to the understanding of ionomer microstructure even in the absence of plasticizer. The interpretation of SAXS data in particular is subject to the choice of model used. 

The interactions of various polar agents with the ionic groups and the ensuing property changes are unique to ionomer systems. This plasticization process is also important in membrane applications. A different application of ionic cluster plasticization involves the interaction of metal stearates to induce softening transitions. The plasticization process is required to achieve the processability of TPEs based on this technology. 

As for polar plasticizers, am enormous amount of work remains to be done to analyze the local structure introduced by different plasticizers around the cations and anions involved, to determine the coordination shells formed, and to generally elucidate the influence of these plasticizers on the ionic intersictions in the ionomer. This knowledge, in turn, must contribute to the determination of correlations between structure and properties in the plasticized systems. 

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. 

Erdi and Morawetz (8) attempted to overcome this problem by incorporating ionic groups into PS in the form of metal carboxylate-containing comonomers. When they plasticized the PS phase in these systems, they observed only a very weak physically bonded network of no substantial strength. However, the availability of these metal-sulfonated ionomers coupled with the inherently stronger associations of the metal sulfonates offer a more attractive system to test this hypothesis. Therefore, plasticized S-PS samples of varying sulfonate level were blended with DOP... 

More recently Dieterich and Reiff (166) have described the formation of aqueous urethane dispersions by the dispersion of ionomer melts with subsequent polycondensation in two-phase systems. The principle of this procedure consists of reacting molten ionic modified polyester or polyether prepolymers containing NCO groups with urea to yield bis(biuret), followed by methylolation by means of aqueous formaldehyde in a homogeneous phase, and the resulting plasticized melt of methylolated ionic urethane bis(biurets) dispersed in water at 50-130 °C. These steps can be represented schematically as follows ... 

A process in which melted plastic is injected into a mold cavity, where it cools and takes the shape of the cavity. Bosses, screw threads, ribs, and other details can be integrated, which allows the molding operation to be accomplished in one step. The finished part usually does not require additional work before assembling. Any IPN in which the individual polymers are thermoplastic. The polymers may contain physical cross-links as in ionomers where ionic clusters join two or more chains together. Nowadays, phase-separated polymeric systems, e.g., block and graft copolymers or thermoplastic polyurethanes, are frequently considered thermoplastic IPNs. 

Maleic anhydride-functionalised polyolefins feature in Solvay s Priex range of compatibilising resins, some of which have very low viscosities so that they can be emulsified in aqueous systems. They are used to compatibilise resins with wood fibres in the production of Wood-Stock wood-plastics composites for the automotive industry. (There is also another type of Priex product, consisting of ionomers designed to improve the mechanical properties of polyolefins.)... 

Stress relaxation experiments performed in the dry state on the aromatic ionomer films were complicated by the hydrophilic nature of the materials. The curves obtained to date are characteristic of the water plasticized system rather than the dry material. More reliably, experiments were... 

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