Highly Efficient Polymerisation Reactions

6 Decomposition of Homogeneous Gold Complexes to Afford Extremely Active Gold Clusters 

More recently, Albercht and coworkers have reported a study on the disproportionation of [Au(trz)Cl] (trz = 1,2,3-triazolylidene) complexes in the presence of silver salts to afford homoleptic and heteroleptic [Au(trz)(L)][X] 

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Carbocations such as t-butyl cation which are sufficiently electrophilic to react efficiently with styrene and linear dienes are themselves highly unstable and cannot be isolated as stable salts. They tend to oligomerise or react readily even with the most stable anions. Of course they can be generated in situ in a polymerisation reaction (1,95),... 

Phenolic products, especially sterically hindered phenols, are widely used throughout the PVC industry - for instance, as chain-stoppers and antioxidants in PVC polymerisation, to terminate the reaction and prevent degradation of the virgin resin in the stripper and dryer. Methyl methacrylate butadiene-styrene (MBS), a frequently used impact modifier for rigid PVC, needs highly efficient protection against oxidative degradation... 

Equation 4.20 shows that mass transfer is a determining factor in anionic polymerisation of PO, a high surface area of the liquid reaction mass giving high rates of PO consumption. On the other hand, due to the very high efficiency of stirring, the gas-liquid contactor reactor type assures a very narrow MW distribution of the resulting polyether. For the ethoxylation of intermediate propoxylated polyethers (in block copolymers PO-EO... 

After having observed that the most active ruthenium-based catalyst systems for olefin metathesis also displayed a high efficiency in atom transfer radical polymerisation, we then became interested in comparing the role of the catalyst in those two different reaction pathways. Ruthenium alkylidene complexes 4-6 are unsaturated 16-electron species which formally allow carbon-halogen bond activation to form a 17-electron ruthenium(III) intermediate. Our preliminary results indicate that polymerisations occur through a pathway in which both tricyclohexylphosphine and/or imidazolin-2-ylidene ligands remain bound to the metal centre. 

This mathematical treatment shows that in the early stages of polymerisation the rate of reaction should be proportional to the square root of the initiator concentration, assuming/is independent of monomer concentration. This assumption is acceptable for high initiator efficiencies, but with very low efficiencies, / may become proportional to [M], making the rate proportional to... 

For the oxygen-initiated polymerisation, nearly 1500 atmosphere pressure and 200°C is used having 0.05-0.1 percentage oxygen. The reaction is highly exothermic and efficient heat dissipation becomes essential. The reaction temperature is above the critical temperature of ethylene so that the ethylene is in the gas phase. 

Among the various methods available for the activation of dienes in a Diels-Alder reaction, Lewis acid catalysis is certainly the most important. Our group has reported the first example of a Diels-Alder reaction catalyzed by Bi(0Tf)3xH20 (Scheme 12) [72], which showed high catalytic activity and regioselectivity in comparison to other Sc-, Ti-, Sm-, or Yb-metal-based Lewis acids, well-known for their efficient catalytic activity. Bi(OTf)3 proved to be slightly more endo-selective than Sc(OTf)3. Further, no polymerisation of dienes or dienophiles was observed. Bi(OTf)3 was also found to be superior to SnCI4 and Cu(BF4)2. 

Microemulsions are used as reaction media for a variety of chemical reactions. The aqueous droplets of water-in-oil micro emulsions can be regarded as minireactors for the preparation of nanoparticles of metals and metal salts and particles of the same size as the starting microemulsion droplets can be obtained [1-3]. Polymerisation in micro emulsions is an efficient way to prepare nanolatexes and also to make polymers of very high molecular weight. Both discontinuous and bicontinuous micro emulsions have been used for the purpose [4]. Microemulsions are also of interest as media for enzymatic reactions. Much work has been done with lipase-catalysed reactions and water-in-oil microemulsions have been found suitable for ester synthesis and hydrolysis, as well as for transesterification [5,6]. 

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