Precursor polymer preparation reaction

Poly(arylene vinylenes). The use of the soluble precursor route has been successful in the case of poly(arylene vinylenes), both those containing ben2enoid and heteroaromatic species as the aryl groups. The simplest member of this family is poly(p-phenylene vinylene) [26009-24-5] (PPV). High molecular weight PPV is prepared via a soluble precursor route (99—105). The method involves the synthesis of the bis-sulfonium salt from /)-dichloromethylbenzene, followed by a sodium hydroxide elimination polymerization reaction at 0°C to produce an aqueous solution of a polyelectrolyte precursor polymer (11). This polyelectrolyte is then processed into films, foams, and fibers, and converted to PPV thermally (eq. 8). 

Mohanty et al. were the first to introduce pendent r-butyl groups in die polymer backbones. The resulting material was quite soluble in aprotic dipolar solvents.83 The PEEK precursors were prepared under a mild reaction condition at 170°C. The polymer precursor can be converted to PEEK in die presence of Lewis acid catalyst A1C13 via a retro Friedel-Crafts alkylation. Approximately 50% of die rerr-butyl substitutes were removed due to die insolubility of the product in die solvent used. Later, Risse et al. showed diat complete cleavage of f< rf-butyl substitutes could be achieved using a strong Lewis acid CF3SO3H as both die catalyst and the reaction medium (Scheme 6.15).84... 

In addition to providing many new precursors to functionalized poly(alkyl/arylphosphazenes), the deprotonation/substitution reactions of these N-silylphosphoranimines serve as useful models for similar chemistry that can be carried out on the preformed polymers. New reactions and experimentation with reaction conditions can first be tried with monomers before being applied to the more difficult to prepare polymeric substrates. A considerable amount of preliminary work [e.g., with the silylated monomers (z z) and polymers (2 o) has demonstrated the feasibility of this model system approach. 

New methods are being developed in various laboratories to synthesize well-defined networks exhibiting structures as close as possible to ideality. The principle of these so-called endlinking methods is to separate the polymerization process from the network-forming reaction. The first step aims at preparing a linear precursor polymer, fitted at both ends with reactive groups. In the second step bonds are established between several precursor chain ends to form the crosslinks. The methods which were used to synthesize so-called model networks have already been described, and we shall only summarize them here ... 

This route was described more or less simultaneously by Karasz et al. 235) and by Murase et al.236). The precursor polymer is typically prepared by reaction of the appropriate bis(chloromethyl)arylene compound with dimethylsulfide in a polar solvent237,238). The product is a water-soluble polymer which can be cast to give thin films. Elimination of hydrochloric acid and dimethyl sulfide takes place on heating the film in the range 200 to 300 °C and can be monitored by thermogravimetry and by the development of colour and conductivity 239. Poly(p-phenylene vinylene), prepared by the precursor route, can be doped to much higher conductivities than the conventionally synthesised polymer. 

Aza-2,4-cyclopentadienone and 3-aza-2,4-cyclopentadienone are two reactive intermediates (75AG38) whose existence has been demonstrated by using the three-phase test. The precursor polymers for both compounds have been prepared (36) from maleimide, which was reduced with LiAlH4 and linked to the sulfonic polymer, and (39) by reaction between (37) and (38) (88JA4017 91JOC5417). 

Even sodium methacrylate5S) can act as an unsaturated deactivator for living poly-THF. The reaction is slow but by a proper choice of the experimental conditions the macromonomers can be obtained in high yields55 without any change in molecular weight (with respect to the precursor polymer deactivated with sodium phenolate). The macromonomers thus obtained contain a methacrylic ester function at the chain end. They are identical with those prepared by cationic initiation with methacryloyl hexafluoroantimonate ... 

One of the most innovative and useful techniques for the preparation of conducting polymers has been the synthesis of highly soluble precursor polymers that can be easily handled in solution, purified, and then later converted to the less tractable conducting polymer. The first example of such an approach was the dehydrohalogenation of poly(vinyl chloride) (102). This reaction, like most elimination reactions on polymers, rarely goes to completion and is not well suited for the synthesis of useful conducting... 

An excellent example of the use of Suzuki polycondensation is the synthesis of ladder-type PPPs (67) (see Scheme 6.16) [84]. A precursor polymer 79 is prepared by AA-BB coupling and then converted to the ladder polymers by polymer analogous reactions. Reduction followed by ring closure with boron trifluoride produces a polymer (67a) with bridgehead hydrogens, while addition of methyl lithium instead of reduction leads to Me-LPPP (67b) with methyls at the bridgeheads. 

Polyheterocycles can even be made by polymer analogous reactions. A good example of this is the formation of oxadiazole-containing polymers. Thus, Janietz et al. [86] prepared the precursor polymers 89 by the polycondensation of 90 with 91 and then dehydrated it with phosphorus oychloride to give the phenylene oxadiazole copolymers 69 (Scheme 6.21). 

Nevertheless, the resulting PPPs are not structurally perfect, as the aromatization process gives rise to mixed para and ortho linkages (15% ortho) and to interchain side-reactions leading to cross-linking. A nonbacterial synthesis of ci.v-diesters of cyclohexadiene followed by a stereospecific polymerization has been developed by Grubbs and coworkers to prepare a totally para precursor polymer [90] (Fig. 9.9). 

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