Hexadiene polymers, molecular

Most joint replacements utilize polymers to some extent. Finger joints usually are replaced with a poly(dimethylsiloxane) Insert and over h00,000 such replacements are made each year (l). More recently a poly(1, -hexadiene) polymer has been tried in this application (l). Many other parts of the hand, such as the bones, have also been replaced by silicone rubber. Other types of joints, such as the hip or the knee, often involve the contact of a metal ball or rider on a plastic surface which is usually made from high density, high molecular weight polyethylene. These metal and plastic parts are usually anchored in the body using a cement of poly(methyl methacrylate) which is polymerized in situ. Full and partial hip prostheses are implanted about... 

The polymers of 1,4-hexadienes have unusually wide molecular weight distributions. This is illustrated by the gel permeation chromatogram of the methanol-insoluble fraction of poly(5-methyl-1,4-hexadiene) in tetrahydrofuran (Figure 9). The polymer was obtained in 82% conversion and had an inherent viscosity of 2.1 dl./g. in toluene at 25°C. 

The cyclopolymerisation of 1,5-hexadiene leads to polymers of substantially higher molecular weights than the polymerisation of 1-hexene with the same catalysts [498], undoubtedly owing to some steric hindrance of the atom transfer that usually terminates the growth of a polymer chain [30],... 

It is possible not only to achieve high mass conversions of polybutadiene to 1,5-hexadiene but also to create telechelic oligomers in this manner [38-40]. Catalyst selection plays an important role here ruthenium-based catalysts appeared to be best in bringing about clean conversions of high molecular weight unsaturated polymers to their telechelic oligomers [1]. 

Of great industrial interest are the copolymers of ethene and propene with a molar ratio of 1/0.5, up to 1/2. These EP-polymers show elastic properties and, together with 2-5 wt% of dienes as third monomers, they are used as elastomers (EPDM). Since they have no double bonds in the backbone of the polymer, they are less sensitive to oxidation reactions. As dienes, ethylidenenorbomene, 1,4-hexadiene, and dicyclopentadiene are used. In most technical processes for the production of EP and EPDM rubber in the past, soluble or highly disposed vanadium components are used [69]. Similar elastomers can be obtained with metallocene/MAO catalysts by a much higher activity which are less colored [70-72]. The regiospecificity of the metallocene catalysts toward propene leads exclusively to the formation of head-to-tail enchainments. The ethylidenenor-bornene polymerizes via vinyl polymerization of the cyclic double bond and the tendency to branching is low. The molecular weight distribution of about 2 is narrow [73]. 

The next approach for obtaining higher molecular weight polymers was to explore acyclic diene metathesis (ADMET) polymerizations.The aim was to achieve higher molecular weight flame-resistant polymers. We modeled the reaction using aliphatic diene monomers such as 1,5-hexadiene and 1,9-deca-diene under test conditions to optimize conditions before making BPC-derived products. At this point, we decided to functionalize the BPC with an olefin. 

The first successful ADMET polymerisation was reported by Wagener and colleagues [28]. They polymerised 1,5-hexadiene and 1,9-decadiene to 1,4-polybutadiene [with a weight average molecular weight (Mw) of 28 kDa] and polyoctenylene (Mw = 108 kDa), respectively, using a tungsten-based catalyst that required extremely dry conditions to avoid side reactions. Recent advances in the development of very active and stable catalysts now allow the synthesis of various polymer architectures with relative ease. 

Schrock s molybdenum catalyst [Mo] 2, however, produced a low molecular weight polymer when exposed to 2-methyl-l,5-hexadiene [61]. Interestingly, it was shown that the monomer initially dimerized to 2,9-dimethyl-l,5,9-decatriene through metathesis of the unsubstituted vinyl group. Over time, however, the substituted vinyl groups underwent CM with the internal olefins to produce 1,4-polyisoprene. This was the first example of the condensation of... 

In addition to living propylene polymerization, vanadium acetylacetonate complexes have also been shown to be living for 1,5-hexadiene polymerization and 1,5-hexadiene/ propylene copolymerization (Doi et al, 1989). At —78°C, l/Et2AlCl polymerized 1,5-hexadiene to produce a low molecular weight polymer (M = 6600 g/mol, M IM = 1.4) that contained a mixture of MCP and VTM units in a 54 46 ratio. The distribution of these two units varied in 1,5-hexadiene-propylene random copolymers as a function of 1,5-hexadiene incorporation. 

Finally, Coates and coworkers found that bis(phenoxyimine) titanium complex 31 was also capable of living 1,5-hexadiene polymerization and 1,5-hexadiene/propylene copolymerization (Hustad and Coates, 2002). Homopolymerization of 1,5-hexadiene with 31/MAO at 0°C produced a high molecular weight polymer with a narrow PDI (M = 268 000 g/mol, Mw/Mn = 1.27). The polymer showed the presence of two distinct units - the expected MCP units as well as 3-vinyl tetramethylene (3-VTM) units. As shown in Scheme 9.4, the MCP units are proposed to arise from 1,2-insertion of 1,5-hexadiene followed by a 1,2-cyclization. However, an initial 2,1-insertion of 1,5-hexadiene followed by a 1,2-cyclization forms a... 

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