Isoprene monomer

Maleic anhydride has been used in many Diels-Alder reactions (29), and the kinetics of its reaction with isoprene have been taken as proof of the essentially transoid stmcture of isoprene monomer (30). The Diels-Alder reaction of isoprene with chloromaleic anhydride has been analy2ed using gas chromatography (31). Reactions with other reactive hydrocarbons have been studied, eg, the reaction with cyclopentadiene yields 2-isopropenylbicyclo[2.2.1]hept-5-ene (32). Isoprene may function both as diene and dienophile in Diels-Alder reactions to form dimers. 

The usage of isoprene monomer is somewhat limited by price and availabiUty. The historical large usage has been in the production of i7j -l,4-polyisoprene... 

The principal route for production of isoprene monomer outside of the CIS is recovery from ethylene by-product C streams. This route is most viable where ethylene is produced from naphtha or gas oil and where several ethylene plants are located in relatively close proximity to the isoprene plant. Although the yield of isoprene per mass of ethylene is quite low, there is enough ethylene produced to provide a large portion of demand. Because of the presence of / -pentane in these streams which a2eotropes with isoprene, extractive distillation must be used to recover pure isoprene. Acetonitrile is the most common solvent, but dimethylformamide is also used commercially. 

Unlike polyethylene and other simple aikene polymers, natural rubber is a polymer of a diene, isoprene (2-methyl-l,3-butadiene). The polymerization takes place by addition of isoprene monomer units to the growing chain, leading to formation of a polymer that still contains double bonds spaced regularly at four-carbon intervals. As the following structure shows, these double bonds have Z stereochemistry ... 

Figure 5.9 GALDI mass spectrum of natural rubber (from toluene/THF solution) on silver doped graphite matrix. The signal spacing of 68 Da corresponds to the isoprene monomer...

Diene polymers refer to polymers synthesized from monomers that contain two carbon-carbon double bonds (i.e., diene monomers). Butadiene and isoprene are typical diene monomers (see Scheme 19.1). Butadiene monomers can link to each other in three ways to produce ds-1,4-polybutadiene, trans-l,4-polybutadi-ene and 1,2-polybutadiene, while isoprene monomers can link to each other in four ways. These dienes are the fundamental monomers which are used to synthesize most synthetic rubbers. Typical diene polymers include polyisoprene, polybutadiene and polychloroprene. Diene-based polymers usually refer to diene polymers as well as to those copolymers of which at least one monomer is a diene. They include various copolymers of diene monomers with other monomers, such as poly(butadiene-styrene) and nitrile butadiene rubbers. Except for natural polyisoprene, which is derived from the sap of the rubber tree, Hevea brasiliensis, all other diene-based polymers are prepared synthetically by polymerization methods. 

In pepper as in many plants, there are two sources of isoprene monomers the mevalonic acid pathway and the plastidal pool from pymvate and glyceraldehyde-3-phosphate [26], Pepper carotenoid biosynthesis uses the plastidal pathway for the isopentyl pyrophosphate monomers and the resident terpenoid synthases and transferases [27], Using the 5-carbon isoprene pool, the prenyl transferases sequentially... 

The PP is produced by melt-kneading PP, an isoprene monomer and a radical polymerisation initiator, which has a high melt viscosity and a high melt tensile strength and is difficult to cause drawdown. Foamed articles made therefrom have a low density, high closed cell content, good appearance and excellent heat resistance. 

Butyl rubber (HR) is widely used for inner tubes and as a sealant. It is produced using the cationic polymerization with the copolymerization of isobutylene in the presence of a small amount (10%) of isoprene. Thus, the random copolymer chain contains a low concentration of widely spaced isolated double bonds, from the isoprene, that are later cross-linked when the butyl rubber is cured. A representation is shown in structure 5.20 where the number of units derived from isobutylene units greatly outnumbers the number of units derived from the isoprene monomer. The steric requirements of the isobutylene-derived units cause the chains to remain apart giving it a low stress to strain value and a low Tg. 

The isoprene monomer is not readily available from direct cracking processes. Several routes are employed for its synthesis. One route begins with the extraction of isoamylene fractions from catalytically cracked gasoline streams. Isoprene is produced by subsequent catalytic dehydrogenation. 

Production of isoprene in the United States in 1993 was reported to be 276 841 tonnes (United States International Trade Commission, 1994). Production capacities for isoprene in 1987 were estimated to be (thousand tonnes) United States, 199 the Netherlands, 25 Republic of South Africa, 45 Japan, 105 and the former Soviet Union, about 800 (Weitz Loser, 1989). In 1992, isoprene monomer reportedly was produced in Brazil, the Netherlands, Japan, Romania, countries of the former Soviet Union and the United States (Lybarger, 1995). 

Many of the natural-product molecules synthesized by plants are formed by the joining together of isoprene monomers via an addition polymerization. A good example is the nutrient beta-carotene, which consists of eight isoprene units. Find and circle these units within the structure shown here. 

The principal route for production of isoprene monomer outside of the CIS is recovery from ethylene by-product C< streams. 

By contrast, cis- 1,4-polyisoprene is produced in limited amounts, since it is not price competitive with natural rubber (owing to the relatively high costs of manufacturing the isoprene monomer). The same applies to trans- 1,4-polyisoprene, which is more expensive than its natural counterparts gutta percha and balata. 

Natural rubber can be viewed as a polymer formed by addition of isoprene monomers at the ends of the 1,3-diene units (although nature does not prepare it in this manner). 

Isoprene can be polymerized in the laboratory by a radical chain mechanism. As shown in the following equations, the odd electron of the initially produced radical is delocalized onto both C-2 and C-4 by resonance. Either of these carbons may add to another isoprene monomer to continue the chain reaction. If C-2 adds, the process is called 1,2-addition if C-4 adds, the process is called 1,4-addition. (This is similar to the addition of electrophiles to conjugated dienes discussed in Section 11.13 and the addition of nucleophiles to a,/8-unsaturated carbonyl compounds described in Section 18.10.)... 

Homopolymerization of complexed acrylonitrile initiated by a one-electron transfer from isoprene monomer ... 

JSR Corp. Isoprene monomer (IP) C5 fraction from naphtha cracker Low investment cost, energy efficient and low production costs 1 1986... 

Similar to our earlier study (2) some of the materials had a dark band at the phase interface which is believed to be rich in the isoprene component This phenomenon arises from the slow rate of copolymerization of the isoprene monomer with the n-butyl acrylate. The major experimental results of this and succeeding sections are summarized in Table II which shows phase domain dimensions for the several samples. 

A 250-ml reaction vessel was used as the polymerization reactor. Each polymerization reaction was carried out either under static conditions in a freezer, where the container was placed in a bath of glycol, or dynamically, by subjecting the container to agitation in a tank of glycol. Isoprene monomer having a purity of 99.2% was used. All polymerizations were conducted in 10-g containers and cyclohexane at 15°C with a solvent/monomer mass ratio of 9. In a typical polymerization the neodymium catalyst/diethyl aluminium chloride base varied from 150 to 500 pmol per 100 g of isoprene. 

The discovery of. stereospecific polymerization methods, which led to the production of practically pure cis-1,4 polyisoprene (natural rubber contains 85 per cent of this isomer), raises the problem of the economic production of isoprene monomer (bPi.013 = 340c, df =0.681 >). 

Fowler, R, Barker, D, " Isoprene monomer production The London end Southeastern Branch of the Institidion ef Chemical Engineers, Southampton Colley of Technology (21 Jan. 1971). 

While the majority of SBC products possess discrete styrene and diene blocks, some discussion of the copolymerization of styrene and diene monomers is warranted. While the rate of homopolymerization of styrene in hydrocarbon solvents is known to be substantially faster that of butadiene, when a mixture of butadiene and styrene is polymerized the butadiene is consumed first [21]. Once the cross-propagation rates were determined (k and in Figure 21.1) the cause of this counterintuitive result became apparent [22]. The rate of addition of butadiene to a growing polystyryllithium chain (ksd) was found to be fairly fast, faster in fact than the rate of addition of another styrene monomer. On the other hand, the rate of addition of styrene to a growing polybutadienyllithium chain (k s) was found to be rather slow, comparable to the rate of butadiene homopolymerization. Thus, until the concentration of butadiene becomes low, whenever a chain adds styrene it is converted back to a butadienyllithium chain before it can add more styrene. Similar results were found for the copolymerization of styrene and isoprene. Monomer reactivity ratios have been measured under a variety of conditions [23]. Values for rs are typically <0.2, while values for dienes (rd) typically range from 7 to 15. Since... 

Analyzing data Give the chemical formula for the latex (isoprene) monomer and the ethanol-sodium silicate polymer. 

Leber A.P. Overview of isoprene monomer and polyisoprene production processes, Chem.-Biol. Interact. 135-136 (2001) 169-173. 

Historically speaking, the first TPEs belong to the PUR family, but since 1950 they were joined by block polymers assembled from hard blocks of polymeric styrene that are attached to soft blocks of polymeric ethylene and butylene, butadiene, or isoprene monomers, and in the 1960s there appeared hard blocks of polymeric aromatic polyesters joined to soft blocks of oligomeric or polymeric ethers. Still later, hard polyamide blocks derived from aromatic dicar-boxylic acids were combined with soft blocks of aliphatic components and the world of TPEs continues to expand. 

Exposure of the n-type films to either liquid (styrene, methyl methacrylate) or gaseous (ethylene oxide, isoprene) monomers resulted in polymerization. Much of our initial work has focused on grafting of poly(ethylene oxide) (PEO) to (CH)X in an effort to render the (CH)X surface more hydrophilic and to provide covalent attachment of a material capable of functioning as a solid electrolyte (12). Films of n-type (CH)X were exposed to dry (CaH2-treated), gaseous ethylene oxide in the range 55-75°C with initial pressures being ca. 500 torr. Reaction times were typically 5 hours. The films were washed with dry, 02-free methylene chloride to remove non-covalently bound PEO and then with deaerated H2O to protonate oxyanions and remove the NaOH byproduct. The presence of bound PEO after extraction was confirmed by IR spectroscopy. 

Synthetic polyisoprene, prepared by free-radical polymerization of isoprene monomer, is a copolymer of six structurally distinct kinds of isoprene chain units. Unlike natural rubber, which is a regularly repeating Class I structure (cis-1,4), such synthetic polyisoprene does not crystallize. On the other hand, by the use of the appropriate stereospecific catalyst, isoprene monomer can be converted to a regular Class I polymer with the same structure as natural rubber (. ... 

There are 200 carbon atoms between crosslinks on the average. This corresponds to 200/4 = 50 monomer units between crosslinks (see Fig. 1.8 in Chapter 1). Since the formula weight of isoprene monomer (CsHs) = bSgmoP, Me = 50x68 = 3400 g mol ... 

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