Ionomers random

Ethylene-methylmethacrylate sodium ionomer (Random copolymer)... 

Weiss et al. [75] have synthesized Na and Zn salt of sulfonated styrene(ethylene-co-butylene)-styrene triblock ionomer. The starting material is a hydrogenated triblock copolymer of styrene and butadiene with a rubber mid-block and PS end-blocks. After hydrogenation, the mid-block is converted to a random copolymer of ethylene and butylene. Ethyl sulfonate is used to sulfonate the block copolymer in 1,2-dichloroethane solution at 50°C using the procedure developed by Makowski et al. [76]. The sulfonic acid form of the functionalized polymer is recovered by steam stripping. The neutralization reaction is carried out in toluene-methanol solution using the appropriate metal hydroxide or acetate. 

In the past, ionomers have generally consisted of 10-12 mole percent of ions and it is our intention to be consistent with the corresponding random ionomers previously discussed in the literature. In addition to gel permeation chromatography (GPC), H and 3C NMR can readily be utilized to verify the relative amount of monomer successfully incorporated into the block copolymer. For example, the composition of a PMMA-PTBMA diblock can be verified by H NMR ratioing the methyl ester integration (3.5 ppm) to the t-butyl ester integration (1.36 ppm). Figure 1 depicts the t-butyl ster chemical shift which appears reproducibly at 1.J6 ppm. C or FTIR can be utilized in certain instances when H NMR chemical shifts overlap. For... 

Ionomer. Ionomer is the generic name for polymers based on sodium or zinc salts of ethylene-methacrylic acid copolymers in which interchain ionic bonding, occurring randomly between the long-chain polymer molecules, produces solid-state properties. 

EMA ionomers (see Figure 4.30) are speciality thermoplastics copolymerized from ethylene and a small fraction of methacrylic acid, which is then transformed into the salt of sodium, zinc, lithium or another metal randomly distributed along the backbone. The backbone is identical to that of the polyolefins but the pendant groups are different, with a polar and ionic character. 

In the hydrated ionomer membrane, liquid-like water acts as the pore former, pore filler, and proton shuffle. The wafer disfribufion and the random network morphology of aqueous pafhways determine proton conduction at... 

For instance, the Dow experimental membrane and the recently introduced Hyflon Ion E83 membrane by Solvay-Solexis are "short side chain" (SSC) fluoropolymers, which exhibit increased water uptake, significantly enhanced proton conductivity, and better stability at T > 100°C due to higher glass transition temperatures in comparison to Nafion. The membrane morphology and the basic mechanisms of proton transport are, however, similar for all PFSA ionomers mentioned. The base polymer of Nation, depicted schematically in Figure 6.3, consists of a copolymer of tetrafluoro-ethylene, forming the backbone, and randomly attached pendant side chains of perfluorinated vinyl ethers, terminated by sulfonic acid head groups. °... 

Schematic depiction of the structural evolution of polymer electrolyte membranes. The primary chemical structure of the Nafion-type ionomer on the left with hydrophobic backbone, side chains, and acid head groups evolves into polymeric aggregates with complex interfacial structure (middle). Randomly interconnected phases of these aggregates and water-filled voids between them form the heterogeneous membrane morphology at the macroscopic scale (right).

For typical catalyst layers impregnated with ionomer, sizes of hydrated ionomer domains that form during self-organization are of the order of 10 nm. The random distribution and tortuosity of ionomer domains and pores in catalyst layers require more complex approaches to account properly for bulk water transport and interfacial vaporization exchange. A useful approach for studying vaporization exchange in catalyst layers could be to exploit the analogy to electrical random resistor networks of... 

The factors 4 and 4 accormt for the heterogeneity of the interface. The interfacial flux conditions. Equations (6.56) and (6.57), can be straightforwardly applied at plain interfaces of the PEM with adjacent homogeneous phases of water (either vapor or liquid). However, in PEFCs with ionomer-impregnated catalyst layers, the ionomer interfaces with vapor and liquid water are randomly dispersed inside the porous composite media. This leads to a highly distributed heterogeneous interface. An attempt to incorporate vaporization exchange into models of catalyst layer operation has been made and will be described in Section 6.9.4. 

Ionomers are random copolymers of ethylene and methacrylic acid in which the formula for some of the repeating units is as follows ... 

Rees and Vaughn (26) state that this type of ionomer is prepared by high pressure polymerization using free radical initiators. They are presumably random copolymers. The crystallinity as determined by x-ray diffraction is about 10% (26). 

Ionomers differ from polyelectrolytes in the proportion of ionizable groups and often in their physical properties. Polyelectrolytes generally have a higher proportion of ionizable units. Ionomers can be divided according to the distribution of the ionizable units as random, telechelic, block and segmented. 

Most ionomers are transparent since the cross-linking is random, giving rise to no large crystalline regions. The toughness and clarity make ionomers an excellent glass coating material. 

Experiments indicate that the critical strain-to-failure is also affected by the average molecular weight and by material processing history. McGrath40 reported strain-to-break of a non-crystalline ionomer (a poly(arylene-ether) random copolymer, biphenyl sulfone in H form, or bi-phenyl sulfone in H form (BPSH)) is proportional to the length of the chain. We found in our laboratory that the casting procedure also affects the strain-to-break of the solution-cast ionomer film. As shown in Fig. 19, a Nation film cast at near room... 

Similar to Zn-SPS, Cs-neutralized poly(styrene-ran-methacrylic acid) (Cs-SMAA) ionomers exhibit Cs-rich vesicular aggregates that are randomly distributed in a... 

Eisenberg, A. Hird, B. Moore, R.B. A new multiplet-cluster model for the morphology of random ionomers. Macromolecules 1990,23, 4098. 

Preliminary dynamic light scattering experiments for ionomers in THF show that the measured correlation function deviates from a single-exponential function. This may be due to the polydlsperslty of molecular aggregates of ionomers, since the aggregation occurs randomly. 

Our work on the synthesis of model ionomer systems by anionic polymerization is continuing. The architectural effects of these ionomers having controlled structures are being compared with their random counterparts. 

Transport properties of ionomer blends, characterized by a given type of spheroids and the aspect ratio, e/a, can now be analyzed by the effective medium theory discussed in the previous section. In this theory, the two phases are assumed randomly mixed and the probability of finding each phase is equal to its volume fraction f.. The effective conductivity, o, of the composite for either Na+ of OH ions is given by (15) ... 

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