Latex catalysts

In a variation a polyethylene latex is used with monomeric MAM and a fiber reactive agent such as dimethylgloxalmonoureine and a latex catalyst, the process being optionally 2-stage. The modified latex features wrinkle and / ... 

The carboxylic acid groups were converted first to the potassium salt and then to Co(II) salts by addition of cobalt(II) acetate solution to the copolymer latex with agitation in an ultrasonic bath to produce the latex catalysts listed in Table 1. The latexes were purified by ultrafiltration through a 0.1 im cellulose acetate/nitrate membrane (Millipore) until tiie conductivity of the filtrate at 25 C was constant at 40 x lO" ohm l cm"l. Purified latexes contained 1-2% solids. An upper limit of 3 x 10" for the firaction of Co(II) not bound to the latex was established by addition of 1,10-phenanthroline to the ultrafiltrate and UV-visible spectrophotometric analysis of tiie Co(II) complex. By the same criterion, addition of 6 mol of pyridine per mol of Co(II) to form the active catalysts did not extract cobalt ions from the latex. Thus practically dl of the Co(II) was bound to latex. A typical transmission electron micrograph of catalyst RC-1 is shown in Figure 1. 

Table 2. Oxidation of Tetralin Using Latex Catalysts. ... 

Figure 3. Consumption of oxygen by 2,6-di-rm-butylphenol with soluble CoPcTs catalyst (open squares) and with latex catalyst HT-9 (filled squares). Consumption of 0.5 mol O2 per mol 1 requires 15.02 mL of 02-Reproduced from ref. 27 by permission of the American Chemical Society.

Latex-bound transition metal catalysts should be active for a wide variety of reactions of water-insoluble organic compounds in aqueous dispersions. The reactions described here are only a beginning. For practical processes to evolve from this research, methods must be found to recover and reuse the latex catalysts for industrial organic chemical processes, and to... 

Vinylpyridine (23) came into prominence around 1950 as a component of latex. Butadiene and styrene monomers were used with (23) to make a terpolymer that bonded fabric cords to the mbber matrix of automobile tires (25). More recendy, the abiUty of (23) to act as a Michael acceptor has been exploited in a synthesis of 4-dimethylaminopyridine (DMAP) (24) (26). The sequence consists of a Michael addition of (23) to 4-cyanopyridine (15), replacement of the 4-cyano substituent by dimethylamine (taking advantage of the activation of the cyano group by quatemization of the pyridine ring), and base-cataly2ed dequatemization (retro Michael addition). 4-r)imethyl aminopyri dine is one of the most effective acylation catalysts known (27). 

In the Talalay process, the froth is produced by chemical rather than mechanical means. Hydrogen peroxide and an enzyme decomposition catalyst are mixed iato the latex and the mixture placed ia the mold. Decomposition of the peroxide by the added enzyme results ia the Hberation of oxygen which causes the latex mix to foam and fill the mold. The foam is then rapidly chilled and CO2 is iatroduced to gel the latex. The gelled foam is then handled ia a manner similar to that used ia the Dunlop process. 

Butadiene copolymers are mainly prepared to yield mbbers (see Styrene-butadiene rubber). Many commercially significant latex paints are based on styrene—butadiene copolymers (see Coatings Paint). In latex paint the weight ratio S B is usually 60 40 with high conversion. Most of the block copolymers prepared by anionic catalysts, eg, butyUithium, are also elastomers. However, some of these block copolymers are thermoplastic mbbers, which behave like cross-linked mbbers at room temperature but show regular thermoplastic flow at elevated temperatures (45,46). Diblock (styrene—butadiene (SB)) and triblock (styrene—butadiene—styrene (SBS)) copolymers are commercially available. Typically, they are blended with PS to achieve a desirable property, eg, improved clarity/flexibiHty (see Polymerblends) (46). These block copolymers represent a class of new and interesting polymeric materials (47,48). Of particular interest are their morphologies (49—52), solution properties (53,54), and mechanical behavior (55,56). 

Polymerization Reactions. The polymerization of butadiene with itself and with other monomers represents its largest commercial use. The commercially most important polymers are styrene—butadiene mbber (SBR), polybutadiene (BR), styrene—butadiene latex (SBL), acrylonittile—butadiene—styrene polymer (ABS), and nittile mbber (NR). The reaction mechanisms are free-radical, anionic, cationic, or coordinate, depending on the nature of the initiators or catalysts (194—196). 

Styrene—Butadiene Rubber (SBR). This is the most important synthetic mbber and represents more than half of all synthetic mbber production (Table 3) (see Styrene-butadiene rubber). It is a copolymer of 1,3-butadiene, CH2=CH—CH=CH2, and styrene, CgH5CH=CH2, and is a descendant of the original Buna S first produced in Germany during the 1930s. The polymerization is carried out in an emulsion system where a mixture of the two monomers is mixed with a soap solution containing the necessary catalysts (initiators). The final product is an emulsion of the copolymer, ie, a fluid latex (see Latex technology). 

The molecular weight of the polymers is controlled by temperature (for the homopolymer), or by the addition of organic acid anhydrides and acid hahdes (37). Although most of the product is made in the first reactor, the background monomer continues to react in a second reactor which is placed in series with the first. When the reaction is complete, a hindered phenoHc or metal antioxidant is added to improve shelf life and processibiUty. The catalyst is deactivated during steam coagulation, which also removes solvent and unreacted monomer. The cmmbs of water-swoUen product are dried and pressed into bale form. This is the only form in which the mbber is commercially available. The mbber may be converted into a latex form, but this has not found commercial appHcation (38). 

L tcx Monomer Production. ARI Technologies, Inc. has introduced a catalyst system which, it is claimed, can operate at an average bed temperature of 370°C while achieving conversion efficiency in excess of 99.99% on exhaust streams from latex monomer production (see Latex technology). 

More recently there have been developed water- resistant phosphorus-based intumescence catalyst. This commercially available product, as an example Phos-Chek P/30 tradename from Monsanto, can be incorporated (with other water insoluble reagents) into water-resistant intumescent coatings of either the alkyd or latex-emulsion type. These intumescent coatings, formulated ac-... 

Polymer-supported catalysts often have lower activities than the soluble catalysts because of the intraparticle diffusion resistance. In this case the immobilization of the complexes on colloidal polymers can increase the catalytic activity. Catalysts bound to polymer latexes were used in oxidation reactions, such as the Cu-catalyzed oxidation of ascorbic acid,12 the Co-catalyzed oxidation of tetralin,13 and the CoPc-catalyzed oxidation of butylphenol14 and thiols.1516 Mn(III)-porphyrin bound to colloidal anion exchange resin was... 

Latex or emulsion polymers are prepared by emulsification of monomers in water by adding a surfactant. A water-soluble initiator is added, e.g., persulfate or hydrogen peroxide (with a metallic ion as catalyst), that polymerises the monomer yielding polymer particles, which have diameters of about 0.1 pm. The higher the concentration of surfactant added, the smaller the polymer particles. 

The Ziegler-type catalysts contain also a metal-alkyl, like triethylaluminum. They work usually at moderate temperature and pressure. The most active catalysts for polymer hydrogenation are the noble metal complex catalysts, and they can also be used for reduction of elastomers in the latex phase. The most difficult task is the removal of the catalyst from the reaction mixture. The methods used are based on extraction, adsorption, absorption or on their combination. 

Mkaline Fuel Cell The electrolyte for NASA s space shnttle orbiter fuel cell is 35 percent potassinm hydroxide. The cell operates between 353 and 363 K (176 and I94°F) at 0.4 MPa (59 psia) on hydrogen and oxygen. The electrodes contain platinnm-palladinm and platinum-gold alloy powder catalysts bonded with polytetraflnoro-ethylene (PTFE) latex and snpported on gold-plated nickel screens for cnrrent collection and gas distribution. A variety of materials, inclnding asbestos and potassinm titanate, are used to form a micro-porous separator that retains the electrolyte between the electrodes. The cell structural materials, bipolar plates, and external housing are nsnally nickel-plated to resist corrosion. The complete orbiter fuel cell power plant is shown in Fig. 24-48. 

Polymerization conditions with temperatures of 60 °C were mild compared with conventional ATRP in solution, where typically temperatures around 100 °C are applied. Despite these mild conditions, high polymerization rates and high conversion within only 3 h were achieved. Moreover, it could be demonstrated that the catalyst, being covalently bound to the surfactant, can easily be removed by filtering off the latex and subsequent washing with methanol. By this procedure the copper content of the resulting PMMA was reduced from the theoretical value of 0.73% to 0.06% and the polymer appeared colorless while the washing fraction was colored [65]. 

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