Styrene catalyzed polymerization

Block copolymers were synthesized by a combination of fipase-catalyzed polymerization and atom transfer radical polymerization (ATRE). " " At first, the polymerization of 10-hydroxydecanoic acid was carried out by using lipase CA as catalyst. The terminal hydroxy group was modified by the reaction with a-bromopropionyl bromide, followed by ATRP of styrene using CuCE2,2 -bipyridine as catalyst system to give the polyester-polystyrene block copolymer. Trichloromethyl-terminated poly(e-CL), which was synthesized by lipase CA-catalyzed polymerization with 2,2,2-trichloroethanol initiator, was used as initiator for ATRP of styrene. 

Variations on this process include atom transfer polymerization (ATRP), "" which includes metal catalyzed atom transfer, to give the propagating radical as illustrated in Scheme 3 for Cu(I) catalyzed polymerization of styrene using 1-arylethyl chlorides. 

Polymerization of isobutylene, in contrast, is the most characteristic example of all acid-catalyzed hydrocarbon polymerizations. Despite its hindered double bond, isobutylene is extremely reactive under any acidic conditions, which makes it an ideal monomer for cationic polymerization. While other alkenes usually can polymerize by several different propagation mechanisms (cationic, anionic, free radical, coordination), polyisobutylene can be prepared only via cationic polymerization. Acid-catalyzed polymerization of isobutylene is, therefore, the most thoroughly studied case. Other suitable monomers undergoing cationic polymerization are substituted styrene derivatives and conjugated dienes. Superacid-catalyzed alkane selfcondensation (see Section 5.1.2) and polymerization of strained cycloalkanes are also possible.118... 

The change in surface acidity with water content was also demonstrated by the ability of kaolinite to promote acid-catalyzed polymerization (236). Styrene, p-methylstyrene, and p-methoxymethylstyrene polymerized vigorously on kaolinite that was dried at 110°C. At 0.2% wt water content, p-methylstyrene and p-methoxystyrene polymerized and at 0.6% wt water content, only p-methoxystyrene polymerized. The polymerization results are consistent with lower acidity at higher water contents since the susceptibility of these monomers to acid-catalyzed polymerization is in the order p-methoxystyrene > p-methylstyrene > styrene. 

Szwarc and coworkers (232) concluded from kinetic studies of sodium catalyzed polymerizations of vinyl pyridine and styrene that propagation involves two consecutive steps. In the first step, monomer complexes with the catalyst. In the rate-determining second step, the complex rearranges to yield product. For styrene polymerization, the steps were formulated as follows ... 

The most likely ending of this BF3-catalyzed polymerization is the loss of a proton from the carbocation at the end of the chain. This side reaction terminates one chain, but it also protonates another molecule of styrene, initiating a new chain. 

However, ionization of the adducts should be more pronounced in more polar solvents and at lower temperatures if ionization is exothermic. Most vinyl ethers polymerize under these conditions [114]. Nevertheless, traces of iodine may catalyze polymerization, because Lewis acids act as coiniti ators. Moreover, even styrene oligomerizes in the presence of high concentrations of dry HC1 in polar solvents at -78° C [115]. 

Iodine. Iodine successfully initiates or catalyzes polymerization of A-vinyl carbazole, vinyl ethers, and styrenes. It adds to double bonds to form 1,2-diiodosubstituted ethanes which are subsequently ionized in the presence of excess iodine [69,149-151]. Stopped-flow UV studies dem-... 

Kirillov, E., Lehmann, C.W., Razavi, A. etal. (2004) Highly syndiospecific polymerization of styrene catalyzed by allyl lanthanide complexes. Journal of the American Chemical Society, 126, 12240. 

Also indicated in Figure 7.7 is the possibility of acid-catalyzed aromatization of DH to an unreactive dimer (DA). Under neutral conditions, only traces of DA are found. However, when a small amount of CSA is added to styrene undergoing polymerization by auto-initiation, significant levels of DA are formed along with polystyrene of higher than expected MW. We believe this is strong support for the Mayo mechanism since acid would have little affect on the Flory diradical intermediate. 

The thermal polymerization of styrene (5), the alkali catalyzed polymerization of lactams (6) and (as some would have it)... 

A series of a-halopropionates (1-21 and 1-22, X = Cl, Br), model compounds of the dormant polymer terminal of acrylates, are suitable for not only acrylates but also styrenes and acrylamides. Ethyl 2-chlo-ropropionate (1-21, X = Cl) was employed for the controlled radical polymerizations of MA and styrene catalyzed by CuCl/L-1 to afford relatively narrow MWDs (MwIMn 1.5).84 A better controlled polymerization of MA is achieved with the bromides 1-21 and 1-22 (X = Br) in conjunction with CuBr/L-1 to give narrower MWDs (MJMn 1.2).84 A similar result was obtained with the combination of 1-23 and CuBr/L-1 for the polymerization of styrene.166 A nickel-based system with Ni-2 and 1-21 (X = Br) gave another controlled polymerization of nBA.134 The iodide compound 1-21 (X = I) is specifically effective in conjunction with an iodide complex such as Re-1 to induce controlled polymerization of styrene.141... 

Arenesulfonyl halides 1-32 were first employed for the CuCl/L-1 -catalyzed polymerization of styrene in the bulk at 130 °C to give polymers with controlled molecular weights and relatively narrow MWDs [MJ Mn = 1.4—1.8).152 No significant effects were observed with different ring substituents. 

A similar effect of water was observed in the iron-catalyzed polymerization of styrene.76,250 An iron complex is less stable in water than ruthenium and thus considered difficult to use as an active catalyst in such an aqueous suspension system. For example, FeBr2(PPhs)2 (Fe-1, X = Br Figure 2) rapidly decomposes upon exposure to water. However, a Cp-based iron complex (Fe-3 Figure 2) proved effective in living radical suspension polymerizations of acrylates and styrene to give narrow MWDs (MJMn = 1.1 — 1.2).250 These polymerizations are also clearly faster than those in organic media under otherwise similar conditions. 

Kinetic analyses were done for several copper-catalyzed copolymerizations of MMA/nBMA,263 nBA/ styrene,264 266 and nBA/MMA.267 All these studies show that there were no significant differences in reactivity ratio as well as in monomer sequence between the copper-catalyzed and conventional radical polymerizations. Only a difference was observed in the copolymerizations between MMA and ometh-acryloyl-PMMA macromonomers where the reactivity of the latter is higher in the metal-catalyzed polymerizations.267 However, this can be ascribed not to the different nature of the propagating species but to the difference in the time scale of monomer addition or other factors. Simulation has also been applied for the copolymerization study.268... 

Perfluoroalkyl groups are also introduced into block copolymers with methacrylates, acrylates, and styrene (B-46 to B-53), which can be synthesized in scCC>2 or in the bulk.95,315 Amphiphilic block copolymers based on glycopolymer segments (B-54 and B-55) are synthesized by copper-catalyzed polymerizations.321,322 Comonomers with a polyhedral oligomeric silsesquioxane unit afforded hybrid polymers between organic and inorganic components (B-56 and B-57).326... 

For styrene-based random copolymers, functional groups can be introduced into the polymer chains via copolymerization with functional styrene derivatives, because the electronic effects of the substituents are small in the metal-catalyzed polymerizations in comparison to the ionic counterparts. Random copolymer R-6 is of this category, synthesized from styrene and />acetoxystyrene.372 It can be transformed into styrene// -vinylphenol copolymers by hydrolysis.380 The benzyl acetate and the benzyl ether groups randomly distributed in R-7 and R-8 were transformed into benzyl bromide, which can initiate the controlled radical polymerizations of styrene in the presence of copper catalysts to give graft copolymers.209 Epoxy groups can be introduced, as in R-9, by the copper-catalyzed copolymerizations without loss of epoxy functions, while the nitroxide-mediated systems suffer from side reactions due to the high-temperature reaction.317... 

Telechelic PMMA can be obtained from MI-13 with Ni-2 as a catalyst.414 Anthrathene-labeled polystyrene can be synthesized with the copper-catalyzed polymerizations initiated with MI-14 the aromatic tag or probe is located near the midpoint of a polymer chain.415 Dibromoacetates MI-15 and MI-16 are commercially available and effective for methacrylates, acrylates, and styrene with nickel and copper catalysts.134,256,360-362 The resultant telechelic polymers have been subsequently employed for the synthesis of various ABA triblock copolymers. 

Another method is based on the metal-catalyzed polymerization from carbon—halogen bonds in the main-chain units, which was applied for the synthesis of C-3 and C-4.430 For C-3, the main chain polymers with controlled molecular weights were prepared via the copper-catalyzed radical polymerization of tri-methylsilyl-protected HEMA followed by the transformation of the silyloxyl group into 2-bromoisobu-tyrate. The pendant C—Br bonds were subsequently activated by the copper catalysts to polymerize styrene and nBA. A more direct way is employed for C-4 i.e., via conventional radical polymerization of 2-[(2-bromopropinonyl)oxy]ethyl acrylate followed by the copper-catalyzed graft polymerization of styrene and nBA from the C—Br substituent. 

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