High-molecular-weight poly , synthesis methods

Silarylene-disiloxane polymers, which exhibit a wide range of physical properties depending on their composition and structure, have received considerable academic and industrial interest for nearly 50 years.One of the prominent properties of silarylene-disiloxane polymers is their excellent thermal stability. The typical methods employed for the synthesis of silarylene-siloxane polymers are the selfpolycondensation of arylenedisilanols or the copolycondensation of arylenedisila-nols with other bifunctional compounds. We found that the easily accessible 1,4-bis(dimethylsilyl)benzene (p-BSB) could react with water in the presence of a catalytic amount of transition metal (Pd, Pt, Rh, etc.) compounds at room temperature to afford high molecular weight poly[(oxydimethylsilylene)(l,4-phenylene) (dimethylsilylene)] with the evolution of H2 as the only by-product, as shown in Scheme 4.6. ... 

Polymerization ofiVIasked Disilenes. A novel approach, namely, the anionic polymerization of masked disilenes, has been used to synthesize a number of poly(dialkylsilanes) as well as the first dialkylamino substituted polysilanes (eq. 13) (111,112). The route is capable of providing monodisperse polymers with relatively high molecular weight M = lO" — 10 ), and holds promise of being a good method for the synthesis of alternating and block copolymers. 

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). 

The synthesis of monodisperse high molecular weight syndiotactic poly(methyl methacrylate) mentioned above was possible at a polymerization temperature as low as — 95 °C [3]. However, methods to synthesize it at a relatively high temperature or to synthesize its isotactic counterpart remain to be found. When the latter is made available, the synthesis of stereo-complexes of poly(methyl methacrylate) will become the focus of considerable interest. 

Phase-transfer techniques are widely used for the preparation of polymers. For example, potassium fluoride is used to produce poly(etherketone)s under phase-transfer conditions (Scheme 10.18). Use of this reagent allows the chloroaro-matics to be used as starting material as opposed to the more expensive flu-oroaromatics that are usually employed [23]. This method is suitable for the synthesis of high molecular weight semicrystalline poly(ether ketone)s, although the presence of excess potassium fluoride in the reaction mixture can lead to degradation reactions. The use of a phase transfer catalyst can allow the use of water-soluble radical initiators, such as potassium peroxomonosulfate used to promote the free-radical polymerization of acrylonitrile [24],... 

The synthesis of extremely high molecular weight star polymers has been achieved by another method. First divlnyl-benzene is reacted at very low concentration with an anionic Initiator (sec. BuLi) to yield a suspension of poly-DVB nodules fitted with numerous initiating sites. Then styrene Is added, and each Initiating site should give yield to a branch. However, the polydispersity of the samples obtained is very high. 

In a brief summary, we have developed a facile and versatile asalt monomer method for the rapid synthesis of both aliphatic and aromatic polyimides. The salt monomer method has the following advantages over the conventional two-step method. First, the aliphatic-aromatic salt monomers as well as all aromatic, composed of diamines (both aliphatic and aromatic) and aromatic tetracarbox-ylic acids (or their half diesters) are highly reactive and rapidly produce polyimides with high molecular weights in one step by the solid-state thermal poly-... 

The synthesis of high molecular weight PPS via a cationic oxidative polymerization route was inhibited by premature precipitation of PPS. A method for the synthesis of high molecular weight PPS from a soluble precursor under mild conditions was developed. Poly(sulfonium cation) was used as a precursor to PPS [Eq. (31)] [118]. 

The traditional approach used in poly(imide-siloxane) synthesis is the reaction of aminopropyl-terminated dimethylsiloxane oligomers with aromatic dianhydrides and additional diamines (9-13). Typically, subambient temperatures and dipolar aprotic solvents are used. The resulting high-molecular-weight polyamic acid solution can be heated to effect imidization and solvent evaporation. This procedure is analogous to the synthetic method used to prepare conventional polyimides for films and coatings. 

MBR have also found use in the production of polysaccharides. MBR provide a simplified method for producing these materials, which are, typically, obtained in small quantities from natural sources by elaborate procedures. Hicke et al. [4.64] reported the synthesis of inulin (poly-j8-(2,l)-frutan) in a MBR with the aid of fructosyltransferase immobilized in the membrane s porous structure. Inulin, with a high molecular weight and low polydispersity, was continuously synthesized from sucrose, as the substrate passed through the MF membrane. 

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