Phosphonium salts, polymer-based

Phosphonium Salt—Urea Precondensate. A combination approach for producing flame-retardant cotton-synthetic blends has been developed based on the use of a phosphonium salt—urea precondensate (145). The precondensate is appUed to the blend fabric from aqueous solution. The fabric is dried, cured with ammonia gas, and then oxidized. This forms a flame-resistant polymer on and in the cotton fibers of the component. The synthetic component is then treated with either a cycUc phosphonate ester such as Antiblaze 19/ 19T, or hexabromocyclododecane. The result is a blended textile with good flame resistance. Another patent has appeared in which various modifications of the original process have been claimed (146). Although a few finishers have begun to use this process on blended textiles, it is too early to judge its impact on the industry. 

However, thermolysis of the phosphonium salts (X=+PPh3) leads directly to the indolic products without need of acid catalyst or PPh3, and thus may not proceed via a normal Wittig pathway. Alternatively, Hughes has effected a solid-phase version of this reaction employing a polymer-hound phosphonium salt and potassium tert-butoxide as base <96TL7595>. In this case, the phosphine oxide by-product remains bound to the polymer resin. 

Under these reaction conditions, the use of ammonium and related onium salts with nucleophilic anions has been found effective at converting the HCl/SnCU-initiated, uncontrolled polymerizations into controlled/ living processes [105], Similar results are reported for TiCl4-based polymerizations [174,175], Effective salts include tetraalkylammonium and phosphonium salts R4N+Y and R4P+Y (Y = I, Br, Cl, CH3COO R = CH3, C2Hs, 71-C4H9, etc.). As added nucleophiles do in nonpolar solvents, the added salts retard the polymerization, narrow the MWD of the polymers, and render their M values directly proportional to conversion and close to the calculated values (one living chain per initiator molecule). 

The theoretical treatment above is based on the assumption that ion pairing is intramolecular. Hence, it is only valid for low conversions of monomer to polymer. If low molecular weight polymer or a phosphonium salt were introduced the polymerization rate fell by two orders of magnitude. At higher polymer concentrations it seems that intermolecular contact ion pairs form. Added water also decreases the rate, perhaps partly because termination reduces the average molecular weight of the polymer at a given conversion. 

The phosphorous-carbon bond in phosphonium salts is readily cleavable by the aid of a base in the absence of aldehydes. Hence, the polymer-bound phosphonium salt 128 offers a direct access to methylarenes 129 (Scheme 16.31). An interesting feature of this linker is the fact that carbonyl compounds can be olefi-nated and this leads to a cleavage-olefmation linker system [126, 127]. 

The iodonium and sulfonium salts have found the most application in both the photoinitiation of polymerization and polymer-based photoimaging. Amenability of these salts to spectral sensitization by either an electron-transfer [21] or a triplet energy transfer pathway [22] is an important factor. The reduction potential of the phosphonium salts, -2.1 to —1.55 V versus SCE [10], is too negative for efficient electron transfer sensitization from most sensitizers of practical interest (see below). As a result, most of the fundamental studies have focused on the iodonium and sulfonium salts, as will this review. 

Polymer-bound triphenylphenylphosphine [354] has been converted to a phosphonium salt 8i by reaction with 2-nitrobenzyl bromide. The nitro group was then reduced to an amine and acylated. The resulting product formed a resin-bound ylide in the presence of base, which underwent a Wittig reaction with aldehydes that released alkenes into solution with the phosphine oxide by-product remaining bound to the solid support [355]. 

Polymer-bound phosphonium salts 9 form after activation with base the intermediate ylides 10 which can be multidirectionally cleaved by reaction with aldehydes R -CHO to form products of type 11.356... 

Polymer-based phosphonium salt Tetra-n-butylammonium bromide 2-Acoxythioethers from oxido compds and thiolic acid esters Regiospecific ring opening 0... 

A mixture of 2-(phenoxymethyl)oxirane, S-phenyl thiobenzoate, and a little Bu4NBr in dry DMF stirred at 110° for 25 h - 2-benzoyloxy-3-(phenylthio)propyl phenyl ether. Y 71% (82.4% conversion). F.e. and with 18-crown-6-metal complexes s. T. lizawa et al., Bull. Chem. Soc. Japan 62, 597-8 (1989) with a polymer-based phosphonium salt cf. Chem. Letters 1988, 1605-8. 

The cyclic diether, 1,3-dioxolane, is recommended by Ferro Corporation as a more benign solvent substitute for chlorinated organic solvents, such as methylene chloride, 1,2-dichloroethane, and 1,1,1-trichloroethane, and for ketones, such as methyl ethyl ketone (MEK). This ethylene glycol-based ether is a suitable solvent under neutral and basic conditions in several major-use areas. It is a powerful solvent for softening and dissolving polymers made from polar monomers, for example, polycarbonates, acrylates, cellulosics urethanes, phenoUcs, nitriles, urea-formaldehydes, and alkyds, as well as polyesters, vinyl epoxys, and halogen-containing polymers. As a reaction solvent it is added as a component to a special quaternary ammonium or phosphonium salt solution for preparation of a vesicular phenoxy resin. Other beneficial uses for the solvent dioxolane, include ... 

Other most successful durable treatment is based on tetrakis (hydroxymethyl) phosphonium derivatives. Very well-known brand marketed as Proban CC (Rhodia, previously Albright Wilson) involves padding of tetrakis (hydroxymethyl) phosphonium chloride (THPC) urea solution onto the cotton fabric, curing with ammonia in a specially designed reactor to generate a highly cross-linked three-dimensional polymer network. The fabric is then treated with hydrogen peroxide, which converts P3+ to the P5+ state. The reactions are shown in Scheme 24.2. Other similar commercial product is Thor s Aflammit P. In literature many combinations of tetrakis (hydroxymethyl) phosphonium derivatives with other salts have been reported,50 but the most successful so far has been the THPC-urea-NH3 system discussed earlier. 

Because these fire-retardant salts are water-soluble and subject to leaching, several new methods have been developed which provide a water-resistant or permanent treatment for cotton fabrics and cellu-losic materials. Perkin developed a process involving successive treatment with sodium stannate and ammonium sulfate, which precipitates stannic oxide in the cellulose libers. Antimony oxide in combination with vinyl chloride or other chlorinated polymers has also been found effective. A more recent approach to this problem involves application of fire-retardant resin-forming or cross-linking compounds. " These include materials and methods based on the copolymerization of tetrakis(hydroxymethyl)phosphonium chloride and methylol — melamine, the reaction of bromoform and triallyl phosphate to form a cross-linked polymer, and the cross-linking reaction of tris(l-aziridinyl)phosphine oxide with cellulose, or its copolymerization with tetrakis(hydroxymethyl)phosphonium chloride and other materials. ... 

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