Isoprene copolymerization

Monomer reactivity ratios and copolymer compositions in many anionic copolymerizations are altered by changes in the solvent or counterion. Table 6-12 shows data for styrene-isoprene copolymerization at 25°C by n-butyl lithium [Kelley and Tobolsky, 1959]. As in the case of cationic copolymerization, the effects of solvent and counterion cannot be considered independently of each other. For the tightly bound lithium counterion, there are large effects due to the solvent. In poor solvents the copolymer is rich in the less reactive (based on relative rates of homopolymerization) isoprene because isoprene is preferentially complexed by lithium ion. (The complexing of 1,3-dienes with lithium ion is discussed further in Sec. 8-6b). In good solvents preferential solvation by monomer is much less important and the inherent greater reactivity of styrene exerts itself. The quantitative effect of solvent on copolymer composition is less for the more loosely bound sodium counterion. 

Table 4.11. Nitrogen balance on isoprene copolymerization with decomposition products of bis(nitrosoacetyl)benzidine (NAB)b 0...

As previously noticed, butyl rubber (HR), poly(methylpropene-co-2-methyl-1,3-butadiene), is a random copolymer of isobutene and 0.7-2.2 mol% of isoprene. The industrial slurry process used all over the world consists in a low-temperature copolymerization initiated by A1C13 in meth-ylchloride. In contrast to 1,3-butadiene, isoprene copolymerizes readily with the more reactive isobutene. Reactivity ratios of the pair isobutene-isoprene, ri = 2.5 0.5 and r2 = 0.4 0.1, measured at the conditions of industrial process [10], show that the copolymerization behaves ideally (ri-r2 = 1), and, at the used low concentration of isoprene, isolated units of this latter comonomer are randomly distributed along the chain with 90% M-p-aiw-enchainment [52,53] ... 

Trcns-1,3-pentadiene and isoprene copolymerize with Ti(On-Bu)4/ AlEta [293]. Isoprene units in the copolymer chain are predominantly of 3,4 structure while the pentadiene units are mixed of cis and trans 1,4, 1,2 and 3,4 structure composition was independent of Al/Ti ratio. Kinetic measurements were not reported but reactivity ratios (Table 26) show somewhat greater reactivity of the pentadiene and a tendency for alternation. 

A plot of the mole fraction of isoprene in the SFR prepared copolymers as a function of the mole fraction of isoprene in the feed is shown in Figure 2. The data points are the results for the SFRP process initiated with BPO at 125 C in the presence of TEMPO the curve represents data reported by Wiley and Davis (6) for a conventional styrene/isoprene copolymerization initiated with peroxide at 100 C. The... 

The surprising result is that the fastest rate constant is associated with the crossover reaction of the poly(styryl)lithium chain ends with butadiene monomer (/isb) conversely, the slowest reaction rate is associated with the crossover reaction of the poly(butadienyl)lithium chain ends with styrene monomer ( gg). Similar kinetic results have been obtained for styrene-isoprene copolymerization [204]. 

Isobutylene and isoprene copolymerize to give butyl rubber. Draw the structure of the repeating unit in butyl rubber, assuming that the two monomers alternate. 

Niu H, Dong J-Y (2015) Regio-chemistry control in propylene/ isoprene copolymerization by metallocene cateilysts. Polym Int 64(8) 1023-1029. doi 10.1002/pi.4878... 

G-5—G-9 Aromatic Modified Aliphatic Petroleum Resins. Compatibihty with base polymers is an essential aspect of hydrocarbon resins in whatever appHcation they are used. As an example, piperylene—2-methyl-2-butene based resins are substantially inadequate in enhancing the tack of 1,3-butadiene—styrene based random and block copolymers in pressure sensitive adhesive appHcations. The copolymerization of a-methylstyrene with piperylenes effectively enhances the tack properties of styrene—butadiene copolymers and styrene—isoprene copolymers in adhesive appHcations (40,41). Introduction of aromaticity into hydrocarbon resins serves to increase the solubiHty parameter of resins, resulting in improved compatibiHty with base polymers. However, the nature of the aromatic monomer also serves as a handle for molecular weight and softening point control. 

AlkyUithium compounds are primarily used as initiators for polymerizations of styrenes and dienes (52). These initiators are too reactive for alkyl methacrylates and vinylpyridines. / -ButyUithium [109-72-8] is used commercially to initiate anionic homopolymerization and copolymerization of butadiene, isoprene, and styrene with linear and branched stmctures. Because of the high degree of association (hexameric), -butyIUthium-initiated polymerizations are often effected at elevated temperatures (>50° C) to increase the rate of initiation relative to propagation and thus to obtain polymers with narrower molecular weight distributions (53). Hydrocarbon solutions of this initiator are quite stable at room temperature for extended periods of time the rate of decomposition per month is 0.06% at 20°C (39). 

Polymers account for about 3—4% of the total butylene consumption and about 30% of nonfuels use. Homopolymerization of butylene isomers is relatively unimportant commercially. Only stereoregular poly(l-butene) [9003-29-6] and a small volume of polyisobutylene [25038-49-7] are produced in this manner. High molecular weight polyisobutylenes have found limited use because they cannot be vulcanized. To overcome this deficiency a butyl mbber copolymer of isobutylene with isoprene has been developed. Low molecular weight viscous Hquid polymers of isobutylene are not manufactured because of the high price of purified isobutylene. Copolymerization from relatively inexpensive refinery butane—butylene fractions containing all the butylene isomers yields a range of viscous polymers that satisfy most commercial needs (see Olefin polymers Elastomers, synthetic-butylrubber). 

Butyl rubber and other isobutylene polymers of technological importance iaclude various homopolymers and isobutylene copolymers containing unsaturation achieved by copolymerization with isoprene. Bromination or chlorination of the unsaturated site is practiced commercially, and other modifications are beiag iavestigated. 

A living cationic polymeriza tion of isobutylene and copolymeriza tion of isobutylene and isoprene has been demonstrated (22,23). Living copolymerizations, which proceed in the absence of chain transfer and termination reactions, yield the random copolymer with narrow mol wt distribution and well-defined stmcture, and possibly at a higher polymerization temperature than the current commercial process. The isobutylene—isoprene copolymers are prepared by using cumyl acetate BCl complex in CH Cl or CH2CI2 at —30 C. The copolymer contains 1 8 mol % trans 1,4-isoprene... 

The refined grade s fastest growing use is as a commercial extraction solvent and reaction medium. Other uses are as a solvent for radical-free copolymerization of maleic anhydride and an alkyl vinyl ether, and as a solvent for the polymerization of butadiene and isoprene usiag lithium alkyls as catalyst. Other laboratory appHcations include use as a solvent for Grignard reagents, and also for phase-transfer catalysts. 

Copolymerization of methacrylic acid with butadiene and isoprene was photoinitiated by Mn2(CO)io without any halide catalyst [28,29]. The po]ymerization system is accompanied by a Dieis-Alder additive. Cross propagation reaction was promoted by adding trieth-y]aluminum chioride. 

Cationic polymerizations work better when the monomers possess an electron-donating group that stabilizes the intermediate carbocation. For example, isobutylene produces a stable carbocation, and usually copolymerizes with a small amount of isoprene using cationic initiators. The product polymer is a synthetic rubber widely used for tire inner tubes ... 

A generic scheme for nitroxide-mediated copolymerization is shown in Scheme 9.48. The literature through 2001 has been summarized by Davis and Matyjaszcwski.5 A non-exhaustive summary of nitroxide-mediated copolymerizalions is provided in Table 9.20 most involve S or isoprene (I). 

In a series of patents17-20, Italian workers disclosed copolymerization of isobutylene and isoprene using Et2AlCl and a host of initiators, e.g. R -C-X, where... 

Pioneering work in living anionic copolymerization of siloxanes was reported by Morton and co-workers 139 140, who synthesized isoprene-dimethylsiloxane block copolymers utilizing D4 as the siloxane monomer. The use of D3 in the synthesis of siloxane block copolymers with controlled structures was demonstrated by Bostick and others. Excellent reviews of these earlier studies and subsequent developments are available in the literature 22 137 13S). 

The reactivities of substituted monomers are different from those of the unsubstituted ones. For example, in crosspropagation an electron donating methyl group introduced to the C = C bond of a vinyl monomer makes it less reactive in anionic copolymerization, while it increases its reactivity in a cationic process. Thus, in THF at 25 °C the reactivity of isoprene towards polystyrene anion is lower by about a factor of 2 than that of butadiene (only one end of this bivalent monomer is affected),... 

The distinction between the rates of homo- and copolymerization apparently is misapprehended by some workers. For example, a recent review 141) discusses the results of McGrath 142) who reported butadiene to be more reactive in polymerization in hexane than isoprene, whether with respect to lithium polybutadiene or polyisoprene, although the homopropagation of lithium polyisoprene in hexane was found to be faster than of polybutadiene. The miscomprehension led to the erroneous statement14l) McGrath 142) results regarding the rate constants for butadiene and isoprene place in clear perspective the bizarre assertion 140) that butadiene will be twice as reactive as isoprene (in anionic co-polymerization). 

Supported Lewis acids are an interesting class of catalysts because of their operational simplicity, filterability and reusability. The polymer-bound iron Lewis-acid 53 (Figure 3.8) has been found [52] to be active in the cycloadditions of a, S-unsaturated aldehydes with several dienes. It has been prepared from (ri -vinylcyclopentadienyl)dicarbonylmethyliron which was copolymerized with divinylbenzene and then treated with trimethylsilyltriflate followed by THF. Some results of the Diels-Alder reactions of acrolein and crotonaldehyde with isoprene (2) and 2,3-dimethylbutadiene (4) are summarized in Equation 3.13. 

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