Isoprene copolymerization with styrene

Effect of Alkali Metal Intiators and Solvents on Copolymerization of Styrene with Isoprene at 25°C... 

But such diagnoses must be very carefully made. The anionic copolymerization of styrene with isoprene in trimethyl aminine with lithium butyl as initiator gives almost the same copolymerization parameters (rs= 0.8,r, = 1.0) as the free radical copolymerization (r5 = 0.4, r, = 2.0), but very different anionic copolymerization parameters are found in other solvents (see also Table 22-17). 

The half-sandwich scandium dialkyl complex combined with [Ph3C][B(C6Fs)4] can also catalyze the syndiospe-cific copolymerization of styrene with isoprene. Because of the excellent living character of this catal5dic system, the... 

Zhang, H., Luo, Y, Hon, Z. Scandium-catalyzed syndiospecific copolymerization of styrene with isoprene. Macromolecules, 41,1064-1066 (2008). 

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). 

It has been emphasized in the copolymerization of styrene with butadiene or isoprene in hydrocarbon media, that the diene is preferentially incorporated. (7,9,10) The rate of copolymerization is initially slow, being comparable to the homopolymerization of the diene. After the diene is consumed, the rate increases to that of the homopolymerization of styrene. Analogously our current investigation of the copolymerization of butadiene with isoprene shows similar behavior. However, the... 

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

In contrast to QM, three monomers of TCK, HCX and CTCX have been found to undergo spontaneous copolymerization with various vinyl monomers such as styrene (St), isoprene, vinyl acetate, acrylonitrile, and methyl methacrylate 58 59,60). For the copolymerization systems of TCX-St, HCX-St, CTCX-St, (Fig. 5) CTCX-... 

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. 

Copolymerization of styrene with diolefins provides further support that monomer coordinates with the cationic site prior to addition. Korotkov (218) showed that in homopolymerizations styrene is more reactive than butadiene, but in copolymerization the butadiene reacted first at its homopolymerization rate and when it was exhausted the styrene reacted at its homopolymerization rate. This interesting result has been duplicated by Kuntz (245) and analogous results have been obtained by Spirin and coworkers (237) for the styrene-isoprene system. Presumably, the diene complexes more strongly than styrene with the lithium and excludes styrene from the site. That the complex occurs at a cationic site, rather than at the anion or the metal-carbon bond, is indicated by the fact that dienes form more stable complexes than styrene with Lewis acids (246). It should be emphasized that selective monomer coordination is not the only factor influencing reactivities in copolymerizations. Of greatest importance are the relative reactivities of the different polymer anions. The more resonance-stabilized anion is more readily formed and is less reactive for polymerizing the co-monomer. 

Considerable efforts have been directed, primarily in Kennedy s group [3], to synthesize a series of block copolymers of isobutene with isoprene [90,91], styrene derivatives [92-104], and vinyl ethers [105-107]. Figure 7 lists the monomers that have been used for the block copolymerizations with isobutene. The reported examples include not only AB- but also ABA- and triarmed block copolymers, depending on the functionality of the initiators (see Chapter 4, Section V.B, Table 3). Obviously, the copolymers with styrene derivatives, particularly ABA versions, are mostly intended to combine the rubbery polyisobutene-centered segments with glassy styrenic side segments in attempts to prepare novel thermoplastic elastomers. These styrene monomers are styrene, p-methylstyrene, p-chlorostyrene, a-methylstyrene, and indene. 

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. 

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]. 

It has an NiAs-type structure (Fig. 15-5), and the isolated methyl groups are presumably in the lattice as the pyramidal CHJ ion.35 Sofiium amd potasstuirralkyl5 can be used for metallation reactions- for example, in eq. 6-2. They can also be prepared from Na or K dispersed on an inert support material, and such solids act as carbanionic catalysts for the cyclization, isomerization or polymerization of alkenes. The so-called alfin catalysts for copolymerization of butadiene with styrene or isoprene to give rubbers consist of sodium alkyl (usually allyl) and alkoxide (usually isopropoxide) and NaCl, which are made simultaneously in hydrocarbons.33... 

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 alkyllithium-initiated copolymerizations of styrene with dienes, especially isoprene and butadiene, have been... 

Hashimoto and coworkers smdied anionic living copolymerization by ionic mechanism of two monomers, styrene and isoprene in a dilute benzene solution with the aid of combined time-resolved... 

Table 22-15. The Anionic Copolymerization of Styrene (Md with Isoprene (M2) with Butyl Lithium as Initiator...

Tapered Block Copolymers. The alkyllithium-initiated copolymerizations of styrene with dienes, especially isoprene and butadiene, have been extensively investigated and illustrate the important aspects of anionic copolymerization. As shown in Table 15, monomer reactivity ratios for dienes copolymerizing with styrene in hydrocarbon solution range from approximately 8 to 17, while the corresponding monomer reactivity ratios for styrene vary from 0.04 to 0.25. Thus, butadiene and isoprene are preferentially incorporated into the copolymer initially. This type of copolymer composition is described as either a tapered block copolymer or a graded block copolymer. The monomer sequence distribution can be described by the structures below ... 

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]. 

A further distinguishing feature of ionic copolymerizations is the strong dependence of reactivity ratios upon the nature of the solvent and the counter-ion (and hence the initiator). These effects can be dramatic and can lead to a reversing of the order of relative monomer reactivities (cf. reactivity ratios for anionic copolymerization of styrene with butadiene and isoprene in different solvents). 

The former process, when applied to isoprene living ends, has been shown to initiate the block copolymerization of styrene with an efficiency of 0.43 if both radical species initiate, or with an efficiency of 0.86 if the organolead radical disproportionates and the polyisoprenyl radical is the sole initiator. 

Free radical copolymerization of methyl methacrylate and styrene as well as butyl methacrylate with styrene or isoprene in toluene under microwave irradiation (monomode microwave reactor) has also been carried out (Fellows, 2005). However, no changes in reactivity ratios were observed although more detailed studies were required for the copolymerization of butyl methacrylate and isoprene. The microwave-assisted polymerization procedure accelerated the polymerizations by a factor of 1.7, may be due to an increase in radical flux. It was proposed that the increased radical flux under microwave irradiation is due to rapid orientation of the radicals that are formed from decomposition of the azoisobutyronitrile. This orientation would reduce the number of direct terminations by recombination of the two radical fragments under microwave irradiation and thus, cause a higher radical flux. 

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. 

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