Acetylene-metal copolymers

Partial hydrogenation of acetylenic compounds bearing a functional group such as a double bond has also been studied in relation to the preparation of important vitamins and fragrances. For example, selective hydrogenation of the triple bond of acetylenic alcohols and the double bond of olefin alcohols (linalol, isophytol) was performed with Pd colloids, as well as with bimetallic nanoparticles Pd/Au, Pd/Pt or Pd/Zn stabilized by a block copolymer (polystyrene-poly-4-vinylpyridine) (Scheme 9.8). The best activity (TOF 49.2 s 1) and selectivity (>99.5%) were obtained in toluene with Pd/Pt bimetallic catalyst due to the influence of the modifying metal [87, 88]. 

The catalysts used in the gas diffusion electrodes for oxygen reduction are from the Pt-group, including this metal itself or rhodium compounds. They are for instance incorporated into graphitized carbon or acetylene black. Binding material is a perfluorinated copolymer (Nafion). The conducting material necessary in the gas diffusion setup is represented by steel or nickel mesh, in some cases silver-plated for better withstanding the 32 wt% caustic alkali. 

The exploitation of active polymer-transition metal bonds for the synthesis of block copolymers (7,8) suggested a potentially viable approach. Specifically, we have attempted to use "living" polystyrene to alkylate Ti(0Bu>4 followed by acetylene polymerization, viz... 

Polymerization of acetylenes by metathesis-type catalysts such as M0CI5 and WCle/PluSn was first observed in the 1970s (Woon 1974 Masuda 1974, 1976), but the nature of the chain carrier was then in some doubt. However, it was soon found (i) that metal carbene complexes would initiate the polymerization of MesCC=CH at 60°C (Katz 1980a) (ii) that end-groups derived from such initiators could be detected in polymers of PhC=CH (Kunzler 1988b) and (iii) that triblock copolymers could be made by successive addition of norbomene, acetylene and norbomene to such initiators (Schlund 1989). All types of acetylene can be polymerized in this way and the reactions proceed by a ROMP-type mechanism see Ch. 10. 

The analysis of the resulting copolymers were established by H NMR, infrared and UV—visible spectroscopies. Table 26 shows the copolymerization results by metal catalysts. The H-NMR spectra of both the monomer and the polymer are shown in Figure 33. As the polymerization proceeded, the acetylenic proton peak at around 1.96 ppm disappeared and a new vinylic proton peak appeared in the aromatic region. Also, the IR spectra of the polymer showed no absorption peaks at 3290 and 2140 cm , which are expected to be present for the acetylenic carbon—hydrogen bond stretching and carbon—carbon triple bond stretching in the monomer, respectively. 

In Chapter 3, Lyudmila M. Bronstein, Valentina G. Matveeva and Esther M. Sulman review metal NP catalysis usingpdymers, in particular, work in Bronstein s group concerning the hydrogenation of drain acetylene alcohols and direct oxidation of L-sorbose. These authors stress the importance of and interest in block copolymers such as pdystyrene-hlock-poly-4-vinylpyridine, PS-b-4VP, and even better poly (ethylene oxide)-block-poly-2-vinylpyridine, PEO-h-P4VP (the latter being used in water). The catalytic efficiency is optimal for the smallest NPs and decrease as the NP size decreases. 

Week [203] developed a monomer salen complex linked to a norbomene via a stable phenylene-acetylene linker and its subsequent polymerization by means of the controlled ROMP method using 3 generation Grubb s catalyst (Scheme 137). This polymerization methodology led to fully functionalized immobilized metal-salen catalyst. By this way, the supported catalyst showed catalytic activities and stereoselectivities similar to the nonsupported Jacobsen catalyst. Moreover, activities and selectivities seemed to depend on the density of the catalytic moieties homopolymer 324 were less selective than their copolymer analogs 325. For example, AE of 1,2-dihydronaphtalene led in both cases to total conversion and 76% ee for the homopolymer 324 vs 81% ee for copolymer 325a. Recycle was possible and after 3 recyles a drastic decrease in ee was observed. AE of dihydronaphtalene led to 81% ee for the first cycle vs 6% ee for the third one. 

By using rare earth metals or radicals it is possible to copolymerize 1,3-butadiene and other dienes with cis-, A linkage [3,498]. Polymers of 1,3-butadiene and isoprene at any ratio can be obtained. Copolymes of 1,3-butadiene and 1,3-pentadiene can be produced with catalysts on the basis of vanadium chelates. 1,3-Butadiene is almost completely converted to trans-, A units, whereas 1,3-pentadiene yields 50 to 60% 1,4-addition and 40 to 50% 1,2-addition products. At a 1,3-pentadiene content of 26 to 45wt%, the copolymers are amorphous, featuring high rigidity [499-501]. Diethylaluminum chloride, nickel naphthenate, and water catalyze the copolymerization of 1,3-butadiene and acetylene. The low-molecular-weight copolymers contain mostly cis-Q-Q double bonds [502]. 

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