Copolymerization butadiene-isoprene

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] ... 

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). 

The general characteristics of anionic copolymerization are very similar to those of cationic copolymerization. There is a tendency toward ideal behavior in most anionic copolymerizations. Steric effects give rise to an alternating tendency for certain comonomer pairs. Thus the styrene-p-methylstyrene pair shows ideal behavior with t = 5.3, fy = 0.18, r fy = 0.95, while the styrene-a-methylstyrene pair shows a tendency toward alternation with t — 35, r% = 0.003, i ii 2 — 0.11 [Bhattacharyya et al., 1963 Shima et al., 1962]. The steric effect of the additional substituent in the a-position hinders the addition of a-methylstyrene to a-methylstyrene anion. The tendency toward alternation is essentially complete in the copolymerizations of the sterically hindered monomers 1,1-diphenylethylene and trans-, 2-diphe-nylethylene with 1,3-butadiene, isoprene, and 2,3-dimethyl-l,3-butadiene [Yuki et al., 1964]. 

Studies of the copolymerization of butadiene, isoprene and styrene with anionic catalysts allow interpretation of the relative anionicity required for polymerizing these monomers. 

An examination of reported reactivity ratios (Table 6) shows that the behaviour rj > 1, r2 1 or vice versa is a common feature of anionic copolymerization. Only in copolymerizations involving the monomers 1,1-diphenylethylene and stilbene, which cannot homopolymerize, do we find <1, r2 <1 [212—215], and hence the alternating tendency so characteristic of many free radical initiated copolymerizations. Normally one monomer is much more reactive to either type of active centre in the order acrylonitrile > methylmethacrylate > styrene > butadiene > isoprene. This is the order of electron affinities of the monomers as measured polarographically in polar solvents [216, 217]. In other words, the reactivity correlates well with the overall thermodynamic stability of the product. Variations of reactivity ratio occur with different solvents and counter-ions but the gross order is predictable. 

This section summarizes the copolymerization of conjugated dienes with other monomers catalyzed by transition metal complexes. Some of the reactions here were also mentioned in the previous section. The catalyst CpTiCl3/MAO is active not only for the polymerization of 1,3-butadiene, isoprene, 1,3-pentadiene, and styrene but also for the copolymerization of these individual monomers [82]. 

Selective solvation has been proved in many cases [233-235]. On the other hand, the behaviour r, 1, Y2 1 is a common feature of anionic copolymerization. One monomer is usually much more reactive to either type of active centre in the order acrylonitrile > methyl methacrylate > styrene > butadiene > isoprene, in agreement with its electron affinity [235]. 

Butadiene-styrene copolymerization was attempted using the L3Ln-RX-AlR3 system [78]. Especially, (CF3COO)3Nd/C5HlxBr/AhBu3 (1 3 15) was found to be active for this type of copolymerization, with the ris-content of butadiene unit amounting 97.8% and the styrene content to ca. 32%. However, for the system of isoprene/styrene, the traws-1,4-polyisoprene copolymer was produced exclusively. 

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]. 

Anionic copolymers, trans-stilbenebutadiene copolymer, trans-stilbene-isoprene copolymer, and trans-stilbene-2,3-dimethylbutadiene copolymer, copolymerized using BuLi initiator, were studied in THE at 0°C and in benzene at 40°C [89]. It was shown that the rate of monomer consumption (excluding stilbene) decreased as follows butadiene > isoprene > 2,3-dimethylbutadiene. Anionic copolymerization... 

The anionic copolymerization (AROCP) of different MSCBs with the monomer of another type capable of anionic polymerization in polar or nonpolar medium initiated by AlkLi mostly yielded random copolymers. The sequential polymerization (addition of the second monomer after polymerization of the first monomer was completed) enabled one to synthesize various block copolymers. As MSCBs, various symmetrically and unsymmetrically substituted derivatives were used. As monomers of other types, styrene, butadiene, isoprene, and 2,4-dimethylstyrene were tested [49]. 

Diolefins, such as butadiene, isoprene, substituted butadienes, 2,4-hexadiene, 1,3-pentadiene, and 1,4-pentadiene, are all known to undergo free-radical-initiated copolymerization with MA. In the absence of initiators, the well-known diene-dienophile reaction can occur to give Diels-Alder products (see Chapter 4). It has also been claimed that it is possible to prepare butadiene-MA copolymers with Ziegler-type catalysts (see Chapter... 

A comparison of the copolymerization properties of butadiene, isoprene, 2,3-dimethylbutadiene, 2,4-hexadiene, 1,3-pentadiene, and 1-methoxybuta-diene with MA is found in Table 10.7. Films obtained by drying solutions of the copolymers were generally tough and flexible. The copolymers contained >75% cw-1,4 unsaturation. 

In general, where the radical derived from JIf is resonance stabilized, the rate of monomer addition will be decreased. In an instance where such a monomer is present to a minor extent in the polymerization feed and fj is low (this means that reaction (xiv) runs at a substantial rate, reaction (xv) at a very slow rate and reaction (xvi) cannot occur readily because is present in such a small amount), the comonomer will be a strong retarder. Examples of such comonomers are butadiene, isoprene, styrene and styrene derivatives, acrylonitrile and fumaronitrile. Although copolymerization can be demonstrated with all of these substances, they retard the polymerization rate so seriously that they might be classed as inhibitors in some concentration ranges. 

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. 

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. 

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). 

Over 5.5 billion pounds of synthetic rubber is produced annually in the United States. The principle elastomer is the copolymer of butadiene (75%) and styrene (25) (SBR) produced at an annual rate of over 1 million tons by the emulsion polymerization of butadiene and styrene. The copolymer of butadiene and acrylonitrile (Buna-H, NBR) is also produced by the emulsion process at an annual rate of about 200 million pounds. Likewise, neoprene is produced by the emulsion polymerization of chloroprene at an annual rate of over 125,000 t. Butyl rubber is produced by the low-temperature cationic copolymerization of isobutylene (90%) and isoprene (10%) at an annual rate of about 150,000 t. Polybutadiene, polyisoprene, and EPDM are produced by the anionic polymerization of about 600,000, 100,000, and 350,000 t, respectively. Many other elastomers are also produced. 

Penultimate effects have been observed for many comonomer pairs. Among these are the radical copolymerizations of styrene-fumaronitrile, styrene-diethyl fumarate, ethyl methacrylate-styrene, methyl methacrylate l-vinylpyridine, methyl acrylate-1,3-butadiene, methyl methacrylate-methyl acrylate, styrene-dimethyl itaconate, hexafluoroisobutylene-vinyl acetate, 2,4-dicyano-l-butene-isoprene, and other comonomer pairs [Barb, 1953 Brown and Fujimori, 1987 Buback et al., 2001 Burke et al., 1994a,b, 1995 Cowie et al., 1990 Davis et al., 1990 Fordyce and Ham, 1951 Fukuda et al., 2002 Guyot and Guillot, 1967 Hecht and Ojha, 1969 Hill et al., 1982, 1985 Ma et al., 2001 Motoc et al., 1978 Natansohn et al., 1978 Prementine and Tirrell, 1987 Rounsefell and Pittman, 1979 Van Der Meer et al., 1979 Wu et al., 1990 Yee et al., 2001 Zetterlund et al., 2002]. Although ionic copolymerizations have not been as extensively studied, penultimate effects have been found in some cases. Thus in the anionic polymerization of styrene t-vinylpyri-dine, 4-vinylpyridine adds faster to chains ending in 4-vinylpyridine if the penultimate unit is styrene [Lee et al., 1963]. 

In the copolymerization of butadiene or isoprene and styrene, the reactivity ratios are influenced by the type of solvent usedJLi Typical conversion curves of a 75/25 butadiene/... 

It was also discovered at Phillips. that the four rate constants discussed above can be altered by the addition of small amounts of an ether or a tertiary amine resulting in reduction or elimination of the block formation. Figures 13 and 14 illustrate the effect of diethyl ether on the rate of copolymerization and on the incorporation of styrene in the copolymer. Indeed, random copolymers of butadiene and styrene or isoprene and styrene can be prepared by using alkyllithium as initiator in the presence of small amounts of an ether or a tertiary amine. 

Anionic Copolymerization of Butadiene and Isoprene with Organolithium Initiators in Hexane... 

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