Homopolymerizations styrene

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. 

For example, random copolymerization of 1-hexene with ethylene was initiated by complex 5(Lu H) [37]. The ratio of ethylene/1-hexene in the polymer of 3 1 indicates the sensitivity of chain propagation toward steric bulk of the incoming monomer. Precatalyst 4(Lu H) effects the random copolymerization of ethylene with methylenecyclopropane to achieve 65 exo-methylenes per 1000 CH2 units [87]. CsMej/ER-ligated Sm complexes 18 can not only homopolymerize styrene... 

Block copolymers of isobutene and styrene can be produced by homopolymerizing styrene in dichloromethane with titanium(IV)chloride and 2-chloro-2-phenylpropane as initiator system to a desired chain length followed by addition of isobutene [597]. At a reaction temperature of —50 °C the molecular weight of the block copolymer is = 45 000 and that of the styrene block is = 29 000. Homopolystyrene and homopoly(isobutene) are removed by extraction with pentane and butanone [598],... 

Note that this inquiry into copolymer propagation rates also increases our understanding of the differences in free-radical homopolymerization rates. It will be recalled that in Sec. 6.1 a discussion of this aspect of homopolymerization was deferred until copolymerization was introduced. The trends under consideration enable us to make some sense out of the rate constants for propagation in free-radical homopolymerization as well. For example, in Table 6.4 we see that kp values at 60°C for vinyl acetate and styrene are 2300 and 165 liter mol sec respectively. The relative magnitude of these constants can be understod in terms of the sequence above. 

Brominated Styrene. Dibromostyrene [31780-26 ] is used commercially as a flame retardant in ABS (57). Tribromostyrene [61368-34-1] (TBS) has been proposed as a reactive flame retardant for incorporation either during polymerization or during compounding. In the latter case, the TBS could graft onto the host polymer or homopolymerize to form poly(tribromostyrene) in situ (58). 

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). 

Addition of dialkyl fumarates to DAP accelerates polymerization maximum rates are obtained for 1 1 molar feeds (41). Methyl aUyl fumarate [74856-71-6] (MAF), CgH QO, homopolymerizes much faster than methyl aUyl maleate [51304-28-0] (MAM) and gelation occurs at low conversion more cyclization occurs with MAM. The greater reactivity of the fumarate double bond is shown in copolymerization of MAF with styrene in bulk. The maximum rate of copolymerization occurs from monomer ratios, almost 1 1 molar, but no maximum is observed from MAM and styrene. Styrene hinders cyclization of both MAF and MAM. 

All this evidence suggests that the radical produced from 2-vinylfuran is a rather strongly stabilized entity, compared with those of more common monomers, and is therefore, not very active in homopolymerization. On the other hand, because of its relative stability, it does not add easily to monomers like styrene, vinylidene chloride or butadiene, and thus the copolymerization rates are also low. Aso and Tanaka86) calculated the values of Q and e as 2.0 and 0.0, respectively. 

Several radical copolymerizations of vinyl 2-furoate with well-known monomers (50 50) were also studied. Complete inhibition was obtained with vinyl acetate, very strong retardation with styrene, vinyl chloride and acrylonitrile methyl methacrylate homopolymerized without appreciable decrease in rate. It is evident that the degree of retardation that vinyl 2-furoate imposes upon the other monomer depends on the stability of the latter s free radical. With styrene and vinyl chloride the small amounts of fairly low molecular-weight products contained units from vinyl 2-furoate which had entered the chain both through the vinyl bond and through the ring (infrared band at 1640 cm-1). 

A more complicated behaviour was obtained with divinyl ether due to the formation of both cyclic structures and pendent vinyl groups in the chain. The failure of such olefins as styrene and isopropenylbenzene to give copolymers with 2-fural-dehyde, and in fact to homopolymerize in its presence, was blamed on the strength of the complex formed between the initiator and the aldehyde, believed too stable to initiate polymerization. 

When one compares the brutto polymerization rate constants, a measure of the reactivity of monomers during cationic homopolymerizations is obtained. It was found for p-substituted styrenes that lg kBr increased parallel to the reactivity, which the monomers show versus a constant acceptor 93). The reactivity graduation of the cationic chain ends is apparently overcomed by the structural influence on the monomers during the entire process of the cationic polymerization. The quantitative treatment of the substituent influences with the assistance of the LFE principle leads to the following Hammett-type equations for the brutto polymerization rate constants ... 

Goodwin et al. (Z2.), Figures 2 and 3, styrene homopolymerization in a batch reactor at 70°C with no added surfactant. 

Sutterlin 22.), Figures 4,5, and 6, styrene and methyl methacrylate (MMA) homopolymerizations in a batch reactor at 80 °C with various amounts of added surfactant. 

Badder and Brooks (2A), Figure 7, styrene homopolymerization in a CSTR at 50 °C with added surfactant. 

Two free radical-initiated polymerizations are used in turn as examples the homopolymerization of methyl methaK rylate and the copolymerization of styrene n-butyl methacrylate. 

Isopropenylferrocene does not homopolymerize under free radical conditions using AIBN as an initiator, but it does copolymerize with styrene.Preliminary results indicate that the IDM monomer also copolymerizes with styrene using AIBN. In benzene solvent at 50°C in 24 h, a 10.6% yield of copolymer (IR vc=0 2020, 1945 cm , vN=0 1675 cm-- -, V q 1601 cm-- -, v 3020 cm-- -) resulted having an M f 5700 and containing 6.8% of IDM as determined by elemental analysis. The initial monomer mixture contained 17% of IDM. 

The DIS monomer, unlike its iron analogue, did not homopolymerize with SnCl initiator even on heating. A plausible reason for this result is that this monomer contains a lone pair of elec-trons available for donation to Lewis acids.JU Thus side reactions similar to those of the previous two monomers would prevent propagation. However, the DIS monomer also underwent a free radical copolymerization reaction with styrene and AIBN initiation. 

Homopolymerization of ethyl 4-vinyl-a-cyano-p-phenylcinnamate with AIBN in benzene gave a soluble polymer of inherent viscosity 0.2 djf,/g. There was no evidence for involvement of the tetra-substituted double bond in the polymerization. Copolymerizations with styrene and methyl methacrylate were also successful. 

Many vinyl monomers were reported to have been grafted onto fluoropolymers, such as (meth)acrylic acid and (meth)acrylates, acrylamide, acrylonitryl, styrene, 4-vinyl pyridine, N-vinyl pyrrolidone, and vinyl acetate. Many fluoropolymers have been used as supports, such as PTFE, copolymers of TFE with HFP, PFAVE, VDF and ethylene, PCTFE, PVDF, polyvinyl fluoride, copolymers ofVDF with HFP, vinyl fluoride and chlorotrifluoroethylene (CTFE). The source of irradiation has been primarily y-rays and electron beams. The grafting can be carried out under either direct irradiation or through the use of preliminary irradiated fluoropolymers. Ordinary radical inhibitors can be added to the reaction mixture to avoid homopolymerization of functional monomers. 

Synthetic applications of carbon radical additions to allenes cover aspects of polymerization, selective 1 1 adduct formation and homolytic substitutions. If heated in the presence of, e.g., di-tert-butyl peroxide (DTBP), homopolymerization of phenylal-lene is observed to provide products with an average molecular weight of 2000 (not shown) [58]. IR and 1H NMR spectroscopic analyses of such macromolecules point to the preferential carbon radical addition to CY and hence selective polymerization across the 2,3-double bond of the cumulene. Since one of the olefinic jr-bonds from the monomer is retained, the polymer consists of styrene-like subunits and may be... 

An interesting feature of the styrene-S02 system, —which indeed is true of all SO2 copolymerizations with comonomers capable of homopolymerizing—, is the existence of a ceiling temperature above which the formation of alternating units, SMS, is forbidden. The number fraction of M sequences of length n is... 

NMP is as successful as RAFT polymerization for the construction of block copolymers. A small library of block copolymers comprised of poly(styrene) (PSt) and poly(ferf-butyl acrylate) (FYBA) was designed and the schematic representation of the reaction is depicted in Scheme 10 [49]. Prior to the block copolymerization, the optimization reactions for the homopolymerization of St and f-BA were performed as discussed in this chapter (e.g., see Sect. 2.1.2). Based on these results,... 

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