Plasticizer ionic domain

In order to enable melt processing of ion containing polymers, such as S-EPDM, it is necessary to introduce a mechanism that weakens the ionic interactions. This can be achieved by the addition of a polar ingredient that would plasticize" ionic domains at elevated temperatures only. A variety of such ionic-plasticizers were described by Makowski and Lundberg (10). A particularly attractive combination was found to be zinc stearate with a zinc salt of S-EPDM. It was shown that for such a combination melt... 

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. 

In order to elucidate the effect of ionic aggregation on the primary relaxation process, it seems useful to reduce the ionic interaction by the introduction of water into the ionic regions. Since water is largely incompatible with the fluorocarbon matrix, although some of it is closely associated with the CF2 groups due to the small size of the aggregates (38), the water-plasticization can be expected to occur preferentially in the ionic domains rather than in the matrix. As will be shown later, however, the proximity of the water does influence the matrix Tg appreciably... 

This is analogous to the well explored ionic domain plasticization effect (43), as a result of which the stress relaxation is accelerated in the plasticized condition over that in the dry state. 

G" and tan 6 versus temperature are depicted in Figure 14. A peak is evident at a. -90°C in tan 6 and G" curves. Judging from the peak temperature, this y relaxation is probably caused by the same mechanism as in the acid and the monovalent salt samples described before. The 3 peak occurs at ca. -20°C and thus overlaps slightly with the y peak. The observation of the 6 region at such a low temperature may be due to the presence of some residual water which would act as a plasticizer within the ionic domains. Other factors may also be present to depress the peak position. 

Therefore, one can expect two types of plasticizing action the more conventional type known in the prior art where a viscosity reduction arises from free volume effects (backbone plasticizers) and a second that acts ideally by diminishing the interchain association of the ionic groups on the polymer chain (ionic domain plasticizers). One would... 

The data thus far have shown that S-PS can be plasticized effectively with respect to backbone and ionic domain plasticizers. By appropriate choice of the plasticizer type either the PS backbone or the ionic domains can be plasticized preferentially. By appropriate control of the metal sulfonate content and the polarity of the plasticizer used, flexible S-PS compositions possessing useful tensile properties are feasible. While this approach has substantial merit, it is apparent that simply increasing the level of a phthalate plasticizer to improve melt flow results in a substantial decrease in useful tensile properties. It would be desirable to use a given level of backbone plasticizer and adjust the melt flow of the entire composition by independently plasticizing the ionic domains. One approach to achieve this objective has been described in the plasticization of ionic groups in metal-sulfonated ethylene propylene terpolymers (9). In those systems, the incorporation of metal carboxylates as plasticizers can improve both flow behavior and tensile properties. It is of interest to determine if this class of plasticizers can be combined with the phthalate plasticizers used for the S-PS backbone to provide an improved balance of flow behavior and tensile properties for S-PS s. 

The addition of ionic plasticizer such as sodium salt of dodecylbenzenesulfomc dramatically increases the ability of the ionomer to ciystallize. Figure 11.11 shows that the heat of fusion of an isothermally crystallized ionomer increases with the addition of a plasticizer. This behavior is attributable to the separation of ionic domains, which enhances the molecular mobility of the crystalhzable chains and also increases the crystallization rate as the amount of plasticizer increases. " ... 

The one general class of polymers that fall outside this concept is the thermoplastic elastomers, one example of which was discussed previously. These materials can be processed (and reprocessed) at high temperature, yet they maintain properties of cured rubber at use temperatures. This system functions by the formation of either hard plastic, crystalline, or ionic domains that, at use temperature, act as cross-link sites because multiple chains are involved in the domains. Upon heating, the integrity of these domains breaks down, and the polymer chains can easily flow past one another. It should be noted that at use temperatures these systems have a three-dimensional network. Such systems tend to show more creep and stress relaxation than cured systems, as the network is formed via weaker secondary effects rather than primary chemical bonds. These problems become more severe as the use temperature is increased because ultimately the network cannot remain intact at processing temperatures. For any network, its structure is important in defining the performance of the... 

This finding is consistent either with a non-spherical structure of the clusters, or with a sphere which deforms when the sample is stretched. It is clear that much further work remains to be done on the elucidation of the shape of the clusters, as well as the geometrical arrangements of the components, i.e. the ions and the polymer chains. This is true not only of the "classical" ionomers, i.e. those based on ethylene, styrene, or the rubbers, but also of the newly developed materials which contain ionic domain plasticizers, consisting of materials such as EPDM ionomers plasticized with zinc stearate. The field should remain a most challenging one in the foreseeable future. 

A plot of the melt viscosity of a typical SPSNa. (1.78 mol% sulfonate) against its Tg value is shown in Figure 6. The viscosity collapse on addition of glycerol causes a sudden drop in Tg, practically eliminating the quasi-cross-linking effect of the ionic clusters. The decrease in Tg upon addition of DOP reflects a classical plasticizing effect on the hydrophobic domains that form the bulk of the polymer41. 

Network structures can also be produced without covalent bonding taking place. They may be produced by ionic linkages or by hydrogen bonding, either directly from one chain to another, via metal ions or via such diverse materials as plasticizer molecules, carbon black particles or even proteinous material. Small crystalline domains in the rubber can also lead to a form of network. 

In gel polymer electrolytes based on PVDF or P(VDF-HFP) plasticized with organic electrolytes such as carbonates, there are two ion-conducting phases. One is the solution filling the pores, which has weak interactions with the pol)uner and is a free solution. The other is in the amorphous domain of the pol)uner. The interaction of the electrolyte solution with the amorphous phase increases the ratio of the amorphous phase by the incorporation of the carbonate this increases the ionic conductivity but decreases the mechanical strength of the porous membrane. The ionic conductivity of the gel polymer electrolyte increases with the amoimt of electrolyte solution, and this increase is larger for samples with lower porosity. This indicates that the ion conduction is mainly along the polymer and less along the pores. The membrane is thermally and mechanically stable up to 100°C, both before and after electrolyte uptake [15]. 

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