1,4-Polyisoprenes, synthesis

Technology for a number of applications of olefin metathesis has been developed (, fO At Phillips, potential processes for producing isoamylenes for polyisoprene synthesis and long-chain linear olefins from propylene have been through pilot plant development. In the area of specialty petrochemicals, potential industrial applications include the preparation of numerous olefins and diolefins. High selectivities can be achieved by selection of catalyst and process conditions. The development of new classes of catalysts allows the metathesis of certain functional olefins (, 14). The metathesis of alkynes is also feasible (15) ... 

The particles of the titanium catalyst 0.03-0.14 pm in diameter, regardless of the conditions of catalytic system preparation, feature low activity in polyisoprene synthesis, and the resulting polymer has a low molecular mass and a narrow MWD. The molecular-mass characteristics of polyisoprene and the activity of the catalyst comprising particles 0.15-4.50 pm in diameter depend to a great extent on its formation conditions. 

Figure 3.9 Stereospecific polymerisation of isoprene (2-methyl-butadiene-l,3). The Russian industry has implemented technologies of c/s-l,4-polyisoprene synthesis with Ti-Al Ziegler-Natta catalysts (synthetic c/s-isoprene rubber SKI-3) and neodymium salts-based lanthanide catalysts SKI-5 grade synthetic rubber (TU 2294-051-16810126-96). SKI-3 rubbers contain up to 93 1% of as-1,4 links, while their content in SKI-5 grade rubber is 96 1%...

Similar change in the rate of stereospecific isoprene polymerisation by microheterogeneons Ziegler-Natta catalysts can also be observed for polyisoprene synthesis with a V-Al catalytic system (Figure 3.15). 

Our time has seen The synthesis of polyisoprene And many cross-linked helixes unknown To Robert Hooke but each primoridal bean Knew cellulose by heart. . . ... 

The revolutionary development of stereospecific polymerization by the Ziegler-Natta catalysts also resulted ia the accomplishment ia the 1950s of a 100-year-old goal, the synthesis of i7j -l,4-polyisoprene (natural mbber). This actually led to the immediate termination of the U.S. Government Synthetic Rubber Program ia 1956 because the technical problem of dupHcating the molecular stmcture of natural mbber was thereby solved, and also because the mbber plantations of the Far East were again available. 

Fetters L.J. and Morton M., Synthesis and properties of block pol3miers. I. Poly(a-methylstyrene)-polyisoprene-poly(a-methylstyrene). Macromolecules, 2, 453, 1969. 

Polybutadiene (PB) and polyisoprene with cis-trans controlled microstructure (synthesis of "natural rubber"). 

The synthesis of transtactic structures is based on catalysts in which the transition metal belongs to the 3d block (Ti, Cr, V, Ni). Particular emphasis is devoted to the synthesis of trans butadiene/piperylene copolymers and to their blends with synthetic cis-l,4-polyisoprene, with the aim of increasing the "green strength" of the latter. 

Abstract Transferases are enzymes that catalyze reactions in which a group is transferred from one compound to another. This makes these enzymes ideal catalysts for polymerization reactions. In nature, transferases are responsible for the synthesis of many important natural macromolecules. In synthetic polymer chemistry, various transferases are used to synthesize polymers in vitro. This chapter reviews some of these approaches, such as the enzymatic polymerization of polyesters, polysaccharides, and polyisoprene. 

Prenyltransferases are responsible for the synthesis of c A-polyisoprene in natural rubber particles but can also be used to synthesize polyisoprenes in vitro. 

Recently Fujiwara et al. reported on the in vitro polymerization of trans-polyisoprene using the enzymes isopentenyl diphosphate isomerase (IDI) and fra 3-isoprenyl diphosphate synthase (IDS) [271]. IDI catalyzes the interconversion of IPP and DMAPP. IDS can now catalyze the polymerization of IPP from DMAPP as outlined above for the synthesis of natural rubber, and as outlined in Fig. 13a. However, the condensation process is inhibited due to hydrophobic interaction between IDS and hydrocarbon of the longer products. The hydrophobic chain of the elongating product does not readily protrude into the aqueous phase and it tends to interact with the enzyme. To achieve an efficient in vitro synthesis, the authors used an organic-aqueous two-liquid phase system to successfully synthesize (low molecular weight) fran.y-polyisoprene (see Fig. 13b). 

It is obvious that transferases are powerful catalysts for the enzymatic synthesis of interesting polymer systems such as polyesters, polysaccharides, and polyisoprenes. Considering the range of reactions that transferases can in principle catalyze, it can... 

In 1965, Milkovich (. ) reported that divinylbenzene could be utilized for the formation of star-branched macromolecules. Later, Rempp and coworkers (2, 3, 4) successfully applied this method for the synthesis of star-branched polystyrenes. Moreover, Fetters and coworkers (54 ) used this procedure for the synthesis of multi-arm star-branched polyisoprene homopolymers and poly-... 

Scheme 22 Synthesis of telechelic acetoxy-terminated cis- 1,4-polyisoprene by olefin metathesis depolymerization of natural rubber [144]...

Amino-terminated telechelic polybutadiene was prepared by LiAlH4 reduction of amidino end-group in polybutadiene, which was polymerised by a water-soluble initiator, 2,2 -azobis(amidinopropane)dihydrochloride. The structure was analysed by 1H- and 13C-NMR, but functionality of 2.0 was obtained by a titration method [70]. Synthesis of co-epoxy-functionalised polyisoprene was carried out by the reaction of 2-bromoethyloxirane with living polymer that was initiated with sec-butyl lithium. The functionality of the resulting polyisoprene was 1.04 by 1H-NMR and 1.00 by thin layer chromatography detected with flame ionisation detection [71]. 

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