Styrene ionic clustering

Plasticization of poly(styrene-b-isobutylene-b-styrene) ionomer by 2-ethylhexyl-p-dimethylaminobenzoate causes a decrease in the glass transition temperature, Tg, as the amount of plasticizer increases (Figure 11.12). This lowering of the Tg indicates that there is a slight plasticization of the non-ionic polystyrene phase. A much larger shift is observed in temperature at which tan5 = 3. This indicates a prefererrtial plasticization of the ionic clusters. 

These multicomponent PP blends have been developed during the last ten years. For example, they comprise (1) either an acidified-PP, its mixture with PP, or a mixture of PP with carboxylic acid-modified EPR (2) poly(methylmethacrylate-co-styrene-co-maleic anhydride) and (3) either ethylene-methylmethacrylate-glycidylmethacrylate, or ethylene-vinylacetate-glycidylmethacrylate. The compatibilization is obtained by chemical reactions between the acid and epoxy groups, as well as by forming ionic clusters capable of forming thermoreversible crosslinks. The blends were used to mold car bumpers and fenders. The products showed good stiffness and low-temperature impact resistance [8]. 

Much emphasis has been placed in recent times on easily recoverable liquid bi-phasic catalysts, including metal clusters in nonconventional solvents. For instance, aqueous solutions of the complexes [Ru3(CO)12.x(TPPTS)x] (x=l, 2, 3 TPPTS = triphenylphosphine-trisulfonate, P(m-C6H4S03Na)3) catalyze the hydrogenation of simple alkenes (1-octene, cyclohexene, styrene) at 60°C and 60 bar H2 at TOF up to 500 h 1 [24], while [Ru i(CO)C (TPPMS) >,] (TPPMS = triphenylphos-phine-monosulfonate, PPh2(m-C6H4S03Na) is an efficient catalyst precursor for the aqueous hydrogenation of the C=C bond of acrylic acid (TOF 780 h 1 at 40 °C and 3 bar H2) and other activated alkenes [25]. The same catalysts proved to be poorly active in room temperature ionic liquids such as [bmim][BF4] (bmim= Tbutyl-3-methylimidazolium). No details about the active species involved are known at this point. 

While ionomers of many types have been made and characterized [1,2,3], there is little work on the overall relaxation mechanisms. For polymers with low ionic concentrations, there is general agreement on the fundamental relaxation step. The stress relaxes by detachment of an ion pair from one cluster and reattachment to another. For the styrene/methacrylic acid Na salt (ST/-MAA-Na) system, there is a secondary plateau in the relaxation modulus which depends on the ionic content and can be described as a rubbery modulus [4], While a rubbery modulus with stress relaxation due to ionic interchange has been invoked earlier, it does not adequately describe the relaxation curves. A different approach is taken here. 

Tphe phenomenon of ion clustering in polymers containing ionic co-monomers has received considerable attention recently, primarily in materials based on styrene, ethylene, or butadiene backbones containing a small concentration of pendant carboxylic acid groups randomly distributed along the chain. These materials have been reviewed in two... 

Styrene-Methacrylic Acid Copolymers and Their Salts. Two different types of experiments were performed with these copolymers. A possible clustering of the ionic groups was studied with copolymers containing protonated styrene monomers and deuterated methacrylic acid groups. The radius of gyration measurements were studied from mixtures of all deuterated chains in a protonated matrix. 

Fig. 2 Mol % ions in multiplets or clusters vs total mol % of ionic comonomer in the styrene ionomers (from dielectric data).

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. 

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