Cyclopentadiene polymerization

The situation is more complicated in the case of the pinacolic rearrangement of the isomeric cyclopentane-1,2-diols (Bunton and Carr, 1963b). In aqueous perchloric acid, cis-1, 2-dimethylcyclopentane-l,2-diol (19) is converted into a mixture of the [Pg.142]

When the reactants are mixed in a 3 1 ratio, an intermediate (7) appearing to contain three o--cyclopentadienyl groups is formed at -80°C. Upon allowing the temperature to rise to -60°C, rearrangement occurs that yields ferrocene and a polymeric cyclopentadiene. The proposed mechanism for this reaction is similar to that proposed in the formulation of Hein s vr-arene chromium complex (2) (Fig. 7). 

Sulfur Transfer. Schmidt and Gbrl reported a successful application of 5,5-dimethyl-l,2-dithia-3,7-diselenacycloheptane in the sulfuration of dienes. The diatomic sulfur species liberated under thermal conditions by the contraction of the diselenotetra-sulflde ring reacted efficiently with several dienes (eq 3). The product disulfides have been obtained from 40% yield for myrcene up to 54% for 2,3-diphenylbutadiene. Apparently, the reaction has its applicability limited to products that have no tendency to aromatize (cyclohexadiene and substituted cyclopentadiene derivatives) or polymerize (cyclopentadiene). 

Gyclopentadiene/Dicyclopentadiene-Based Petroleum Resins. 1,3-Cyclopentadiene (CPD) is just one of the numerous compounds produced by the steam cracking of petroleum distillates. Due to the fact that DCPD is polymerized relatively easily under thermal conditions without added catalyst, resins produced from cycloaHphatic dienes have become a significant focus of the hydrocarbon resin industry. 

Table 4. Effect of Cyclopentadiene—Acyclic Diene Codimers on DCPD-Based Thermal Polymerizations ...

In the process of thermal dimerization at elevated temperatures, significant polymer is formed resulting in seriously decreased yields of dimer. Dinitrocresol has been shown to be one of the few effective inhibitors of this thermal polymerization. In the processing of streams, thermal dimerization to convert 1,3-cyclopentadiene to dicyclopentadiene is a common step. Isoprene undergoes significant dimerization and codimerization under the process conditions. 

Table 3 provides typical specifications for isoprene that are suitable for Al—Ti polymerization (89). Traditional purification techniques including superfractionation and extractive distillation are used to provide an isoprene that is practically free of catalyst poisons. Acetylenes and 1,3-cyclopentadiene are the most difficult to remove, and distillation can be supplemented with chemical removal or partial hydrogenation. Generally speaking distillation is the preferred approach. Purity is not the main consideration because high quaUty polymer can be produced from monomer with relatively high levels of olefins and / -pentane. On the other hand, there must be less than 1 ppm of 1,3-cyclopentadiene. 

Cyclopentadiene itself has been used as a feedstock for carbon fiber manufacture (76). Cyclopentadiene is also a component of supported metallocene—alumoxane polymerization catalysts in the preparation of syndiotactic polyolefins (77), as a nickel or iron complex in the production of methanol and ethanol from synthesis gas (78), and as Group VIII metal complexes for the production of acetaldehyde from methanol and synthesis gas (79). 

As recently as 1986 almost all addition polymers were excluded from the ranks of engineering plastics. However, progress since then has been made in the development of addition polymeric resins such as polymethylpentene and polycyclopentadiene and its copolymers (see Cyclopentadiene AND DICYCLOPENTAD IENE). 

Cyclopentacliene undergoes thermal polymerization to yield a polymer that has no double bonds in the chain. On strong heating, the polymer breaks down to regenerate cyclopentadiene. Propose a structure for the polymer. 

Inhibition of olefin polymerization occurred when its basicity was not sufficient to produce an appreciable displacement of initiator from the aldehyde-acid complex isoprene, cyclopentadiene and styrene were in this category. 

Several different companies have greened various steps of the process. In VNB production by-products come from competing Diels-Alder reactions and polymerization, largely of cyclopentadiene. The reaction is usually carried out in a continuous tube reactor, but this results in fouling, due to polymerization, at the front end, where the dicyclopentadiene is cracked to cyclopentadiene at temperatures over 175 °C. Whilst fouling does not have a very significant effect on yield, over time it builds up. 

See also Acetoacetyl-CoA in citric acid cycle, 6 633 Acetyl cyclohexanesulfonyl peroxide (ACSP), 74 282 78 478 Acetylene(s), 7 177-227, 227-228 25 633 addition of hydrogen chloride to, 73 821 from calcium carbide, 4 532, 548 carbometalation of, 25 117 as catalyst poison, 5 257t chemicals derived from, 7 227-265 decomposition of, 70 614 Diels-Alder adduct from cyclopentadiene, 8 222t direct polymerization, 7 514 economic aspects of, 7 216-217 explosive behavior of, 7 181-187 as fuel, 7 221-222 health and safety factors related to, 7 219... 

In the system cyclopentadiene-trichloroacetic acid-benzene the occurrence of ions during polymerization has been shown, but these arise from the protonation of conjugated double bonds in the polymer. However, there is also circumstantial evidence for the participation of carbonium ions in the growth reaction [24]. 

The experiments show that the dilution of all the monomers leads to a change of rate, and I contend that at the earliest stage of dilution the polymerizations are still mainly unimolecular and I offer an explanation for the effects of solvents on the rate of the unimolecular reactions. Since the rate constants, k, are defined by (4.1) and (4.14) they can only be calculated if [P+ M] is known. As explained in Section 3b, there are reasons for believing that for cyclopentadiene and for isobutene [P+ M = c, but for the former there are no results for solutions, and for the latter no c values are available, so that for these monomers could only be calculated for the bulk polymerizations. 

The second part of the theory, which is a logical consequence of the first, is that monomers that have more than one basic site, e.g., an aromatic ring or an oxygen atom, can form more than one type of complex with the carbenium ion this idea was first proposed by Plesch (1990) in the context of chemically initiated polymerizations. It helps to explain why aryl alkenes and alkyl vinyl ethers polymerize more slowly than isobutene and cyclopentadiene. The reason is that all the complexes formed by the alkyl alkenes are propagators, whereas for the aryl alkenes and vinyl ethers only a fraction of the population of complexes can propagate. 

Taking advantage of the competition principle, Bottini et al. [54] determined relative rate constants (krei) for the interception of 6 by conjugated dienes and styrene. Three precursors of 6 were employed, 32b, 33a and 35 (see Scheme 6.9), and also the solvent and the temperature were varied. If the polymerization of styrene and the dimerization of 1,3-cyclopentadiene are taken into account, the various sets of krei values agree well with each other and indicate the same reactive intermediate 6 under all conditions tried. Obviously, 6 is uncomplexed rather than associated with a metal halide, formed on generation of 6, or magnesium, which is the reagent for the liberation of 6 from 33a. The kre values obtained from experiments with 35 are summarized in Scheme 6.19. 

Cross-linked polymers bearing IV-sulfonyl amino acids as chiral ligands were converted to polymer bound oxazaborolidine catalysts by treatment with borane or bromoborane. In the cycloaddition of cyclopentadiene with methacrolein, these catalysts afforded the same enantioselectivities as their non-polymeric counterparts238. 

In contrast, exposure of 14-VE (diene)MCp Cl complexes (M = Zr, Hf) to CO (1 atm) results in the formation of cyclopentadienes70. The mechanism proposed for this transformation was elucidated with a carbon labeled CO ( CO) as requiring an initial coordination of CO to generate a (diene)MCp (CO)Cl complex 153 (Scheme 37). For the hafnium complex, the intermediate 153 (M = Hf) was observed by infrared spectroscopy. Insertion of CO into the a2, jt diene generates a metallacyclohexenone, which undergoes reductive elimination to generate the dimeric metallaoxirane species 154. -Hydride elimination from 154 (M = Zr, Hf) followed by 1,2-elimination produces substituted cyclopentadienes and the polymeric metal-oxide 155. Treatment of (diene)TiCp Cl with CO leads to isolation of the metallaoxirane complex 154 (M = Ti). 

Saturated 2-vinyl-5(47Z)-oxazolones have been widely used as intermediates for the synthesis of polymeric compounds that will be described in Section 7.3.2.9. Apart from these polymerization reactions, the Diels-Alder reactions of 4-sub-stituted-2-vinyl-5(47/)-oxazolones 134 with cyclopentadiene are reported to give norbomenyl oxazolones 135 that are useful to prepare norbornenyl functionalized resins by azlactone ring-opening addition reactions (Scheme 7.39). 

Recently, Spange et al. (19,20) have successfully achieved cationic graft polymerizations of vinyl ethers, vinyl furan, and cyclopentadiene onto silica, initiated by a stable ion pair formed from silanol and aiylmethyl halide, such as di(p-methoxy-phenyl)methyl chloride. The grafting of the polymer onto silica is proposed to take place via the propagation based on olefin insertion to a cation center being in a rapid equilibrium with the ion pair, as shown in Scheme 12.1.3. 

The phenomenon involving failure of a material subject to repeated loading is called fatigue. Failure occurs at stress levels below those observed in the "static" tests described above. Lee et al (22) examined the characteristics of some sulphur concretes subject to fatigue. Fatigue lives (the number of cycles to failure) considerably in excess of those for portland cement concretes were observed. Polymerization of the sulphur with di-cyclopentadiene was observed to reduce fatigue life. 

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