Copolymerization of Butadiene and Isoprene

The similarity in chemical structure of BD and IP allows the copolymerization by many Ziegler/Natta catalysts. To our knowledge, the first study on Nd-catalyzed copolymerization of BD and IP was reported by Monakov et al. [ 152, 153]. Theses authors copolymerized the two dienes with the catalyst system Nd stearate/TIBA/DEAC in toluene at 25 °C. The respective copolymerization parameters reported in this study are ted = 194 and np = 0.62. 

Shen et al. determined the BD/IP copolymerization parameters for the polymerization with the ternary catalyst system NdN/TIBA/EASC at 50 °C ted = 1.4 and np = 0.6 [92]. Over a wide range of BD/IP copolymer compositions the experimentally determined Tg values significantly deviate from the theoretical curve which was calculated by the Fox equation for random copolymers. Only for IP-contents lOwt. % does the experimentally determined data coincide with the theoretical curve. Shen et al. also succeeded to synthesize block copolymers comprising poly(butadiene) and poly(isoprene) building blocks [92]. 

Hsieh et al. used NdCU-based catalysts for the copolymerization of BD and IP [134]. They determined the following copolymerization parameters ted = 1 and rip = 1. For a copolymer with a 50/50 composition (wt. % based) a single Tg = - 85 °C was found and for the dependence of 1/Tg on copolymer composition a linear relationship was obtained. 

Oehme et al. used the catalyst NdO/TEA/DEAC for the BD/IP-copolymer-ization and determined the reactivity ratio of BD and IP by the method of Kelen-Tiidos pbd = 1-09 and np = 1-32. This is the only study in which Dp pbd [168]. Studies on the copolymerization of BD and IP with the catalyst system NdO/TIBA/EASC performed by the same group showed that the cis- 1,4-content of the BD units decreases with increasing content of incorporated IP [163]. A higher content of incorporated IP results in a lower PDI of the copolymer. The dependence of Tg on copolymer composition indicates a random distribution of BD and IP units in the copolymer. 

The catalyst system Nd(OCOCCl3)3/TIBA/DEAC was used for the copolymerization of BD and IP by Kobayashi et al. [176]. The copolymerization parameters were determined at 0 °C pbd = 1-22 and np = 1.14. This study also revealed that the microstructures of the poly(butadiene) and poly(isoprene) moieties were not influenced by polymerization temperature. 

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

In the current study of the homopolymerization and copolymerization of butadiene and isoprene by secondary-butyllithium in hexane the following conclusions can be made. 

Table 25 Copolymerization parameters rBD and rip for the copolymerization of butadiene and isoprene with Nd catalyst systems ...

Dolgoplosk et al. [301] have reported kinetic data on the polymerization of dienes using 7r-allylic (7r-allyl and TT-crotyl) chromium compounds in solution and deposited on a silica support, and on the copolymerization of butadiene and isoprene using the supported TT-allyl catalyst and a Cr03/Si02 Al2 03 catalyst. Full details of the kinetics. 

Metal-containing polymers are also applied to the catalysis of other processes such as polymerization and copolymerization of butadiene and isoprene (see, e.g., ref. (64)), oopolymerization of diene and olefin monomers and polymerization conversions of acetylene-type monomers (65). Such investigations are likely to be oriented both theoretically and practically. Metallopolymers can be used as advantage in some other catalytic processes (54), among them hydrogenation of imsaturated carpounds, oxidative conversions of hydrocarbons, in hydroformylation, polycondensation and other processes, etc. (Table 4). Catalysis of almost all reactions obeys the same or similar principles as in the case of polymerization. The position of metallopolymers in catalysis and their links with traditional catalysts can be illustrated as follows ... 

Thermal stability of polyurethane elastomers based on a produet of the anionic copolymerization of butadiene and isoprene in the ratio of 80 20 and isoprene was first studied by DSC. The preferred eonditions (temperature of the isothermal segment and oxygen eonsumption) were revealed to determine the oxidation induction time of this type of materials. The effeet of Irganox 1010, Evemox 10, Songnox 1010 and 1010 Chinox stabilizers on the oxidation induction time has been studied. 

Copolymerization of butadiene and isoprene with monobutyl maleate and dialkyl maleates or fumarates is also reported to give equimolar copolymer.The copolymerizations were initiated by UV radiation,electric current, " and conventional free-radical " " initiators. Copolymerization is believed to occur by c/5-1,4 addition, which is explained by participation of a CTC. 

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. 

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/... 

Relatively little information is available for the copolymerization of butadiene with isoprene. In an early paper by Rakova and Korotkov (8), it was concluded that in n-hexane with n-butyllithium as the initiator, the reactivity ratios for butadiene and isoprene were rg = 3.38 and rj = 0.47, respectively. 

This observation is corroborated with what has been found in Figures 8-10. There is more of an inversion phenomenon occurance at 20°C. However, the difference between 30°C and 40°C is small and apparently similar, within experimental error. Nevertheless, the new established reactivity ratios of butadiene and isoprene at all three temperatures differ by a smaller factor than what were reported by the work of Korotkov (8) (e.g. rj - 3.38 and 2 = 0.47). Moreover, butadiene is more reactive and initial copolymer contains a larger proportion of butadiene randomly placed along with some incorporation of isoprene units. The randomness of the copolymer via direct copolymerization has been confirmed by the comparison with pure diblock copolymer produced by sequential monomer addition. Both copolymers have similar chemical composition (50/50) and molecular weight. Their... 

These results show that the 1,2-polymerization of butadiene requires a less anionic catalyst than the anionic polymerization of styrene. Tobolsky and Rogers (58) studied the same effects of catalyst anionicity on the copolymerization of styrene and isoprene. They found that the increased anionic character of the lithium-THF combination relative to butyllithium catalysts increased the styrene content of the polymer as well as decreased the 1.4-structure of the polyisoprene. 

Korotkov and Rakova (53) found that butadiene was more active in copolymerization with isoprene with lithium catalyst, although in homopolymerization isoprene is three times faster. Korotkov and Chesnokova (33) studied the copolymerization of butadiene and styrene with n-butyl lithium in benzene. Butadiene polymerized before much of the styrene was consumed. They claimed the formation of block polymers consisting initially of polybutadiene and the polystyrene chain attached. 

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... 

The mechanistic principle of the chain transfer exploiting functionalized transfer agents was used for the synthesis of polymer bound CB AO, attached to the polymer chain via the sulfur atom. Weinstein [73, 74] used phenolic and aminic thiols 79, 81 and disulfides 80, 82 as generators of thiyls during free-radical bulk or emulsion copolymerization of butadiene or isoprene with styrene. Systems formed can be considered as bifunctional physically persistent stabiUzers combining CB and HD fiinctions. 

Let us assume that we are dealing with an alternating copolymerization of butadiene (or isoprene) with a monomer drastically differing from butadiene. In this case the symmetric diene will be attached all the time to an alien radical active center and, vice versa, an alien monomer will be bonded to a diene radical center. The principle of local symmetry is no longer valid, and in the absence of the Jahn-Teller effect the formation of only the 1,4 (4,l)-structuie of diene units in the copolymer should be expected. 

The possibilities inherent in the anionic copolymerization of butadiene and styrene by means of organolithium initiators, as might have been expected, have led to many new developments. The first of these would naturally be the synthesis of a butadiene-styrene copolymer to match (or improve upon) emulsion-prepared SBR, in view of the superior molecular weight control possible in anionic polymerization. The copolymerization behavior of butadiene (or isoprene) and styrene is shown in Table 2.15 (Ohlinger and Bandermann, 1980 Morton and Huang, 1979 Ells, 1963 Hill et al., 1983 Spirin et al., 1962). As indicated earlier, unlike the free radical type of polymerization, these anionic systems show a marked sensitivity of the reactivity ratios to solvent type (a similar effect is noted for different alkali metal counterions). Thus, in nonpolar solvents, butadiene (or isoprene) is preferentially polymerized initially, to the virtual exclusion of the styrene, while the reverse is true in polar solvents. This has been ascribed (Morton, 1983) to the profound effect of solvation on the structure of the carbon-lithium bond, which becomes much more ionic in such media, as discussed previously. The resulting polymer formed by copolymerization in hydrocarbon media is described as a tapered block copolymer it consists of a block of polybutadiene with little incorporated styrene comonomer followed by a segment with both butadiene and styrene and then a block of polystyrene. The structure is schematically represented below ... 

Electron-withdrawing substituents in anionic polymerizations enhance electron density at the double bonds or stabilize the carbanions by resonance. Anionic copolymerizations in many respects behave similarly to the cationic ones. For some comonomer pairs steric effects give rise to a tendency to altemate. The reactivities of the monomers in copolymerizations and the compositions of the resultant copolymers are subject to solvent polarity and to the effects of the counterions. The two, just as in cationic polymerizations, cannot be considered independently from each other. This, again, is due to the tightness of the ion pairs and to the amount of solvation. Furthermore, only monomers that possess similar polarity can be copolymerized by an anionic mechanism. Thus, for instance, styrene derivatives copolymerize with each other. Styrene, however, is unable to add to a methyl methacrylate anion, though it copolymerizes with butadiene and isoprene. In copolymerizations initiated by w-butyllithium in toluene and in tetrahydrofuran at-78 °C, the following order of reactivity with methyl methacrylate anions was observed. In toluene the order is diphenylmethyl methacrylate > benzyl methacrylate > methyl methacrylate > ethyl methacrylate > a-methylbenzyl methacrylate > isopropyl methacrylate > t-butyl methacrylate > trityl methacrylate > a,a -dimethyl-benzyl methacrylate. In tetrahydrofuran the order changes to trityl methacrylate > benzyl methacrylate > methyl methacrylate > diphenylmethyl methacrylate > ethyl methacrylate > a-methylbenzyl methacrylate > isopropyl methacrylate > a,a -dimethylbenzyl methacrylate > t-butyl methacrylate. 

Random Styrene-Diene Copolymers. Random copolymers of butadiene (SBR) or isoprene (SIR) with styrene can be prepared by addition of small amounts of ethers, amines, or alkali metal alkoxides with alkylhthium initiators. Random copolymers are characterized as having only small amounts of block styrene content. The amoimt of block styrene can be determined by ozonoly-sis or, more simply, by integration of the nmr region corresponding to block polystyrene segments (S = 6.5-6.94 ppm) (180). Monomers reactivity ratios of tb = 0.86 and rs = 0.91 have been reported for copolymerization of butadiene and styrene in the presence of 1 equiv of TMEDA ([TMEDAMRLi] = 1) (181). However, the random SBR produced in the presence of TMEDA will incorporate the butadiene predominantly as 1,2 imits. At 66°C, 50% 1,2-butadiene microstructure will be obtained for copolymerization in the presence of lequiv of TMEDA (134). In the presence of Lewis bases, the amounts of 1,2-polybutadiene enchainment decreases with increasing temperature. 

Polyurethane elastomers (PUE) are of great practical importance in various fields [ 1 ]. In particular, in developing PUE of molding compositions for sports and roofing the liquid rubbers (oligomers) of diene nature with a molecular weight of 2000-4000 are widely used as a polyol component. Usually these are homopolymers of butadiene and isoprene, the products of copolymerization of butadiene with isoprene or butadiene with piperylene and isocyanate prepolymers based on these oligomers. 

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). 

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 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. 

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