Anionic polymerization of styrene

The mechanism of the anionic polymerization of styrenes and 1,3-dienes initiated by alkaU metals has been described in detail (3,20) as shown in equations 3—5 where Mt represents an alkaU metal and M is a monomer molecule. Initiation is a heterogeneous process occurring on the metal surface. The... 

The first unequivocal proof of feasibility of homogeneous polymerization free of termination and chain-transfer was reported in 1956, and the concept of living polymers and its ramifications were fully developed in those publications 2). Although the initial work dealt with anionic polymerization of styrene and the dienes, the underlying ideas were soon applied by other workers to a great variety of polymeric systems, as shown by the brief review of some of those developed recently. 

The mechanism of anionic polymerization of styrene and its derivatives is well known and documented, and does not require reviewing. Polymerization initiated in hydrocarbon solvents by lithium alkyls yields dimeric dormant polymers, (P, Li)2, in equilibrium with the active monomeric chains, P, Li, i.e. 

Some new initiators soluble in hydrocarbons were described during the last few years. Organo-lithium compounds form 1 1 complexes with alkyls of Mg 134,135), Zn 136) or Cd l36), and their usefulness as initiators of anionic polymerization of styrene and the dienes was established 137). 

However, the mechanisms by which the initiation and propagation reactions occur are far more complex. Dimeric association of polystyryllithium is reported by Morton, al. ( ) and it is generally accepted that the reactions are first order with respect to monomer concentration. Unfortunately, the existence of associated complexes of initiator and polystyryllithium as well as possible cross association between the two species have negated the determination of the exact polymerization mechanisms (, 10, 11, 12, 13). It is this high degree of complexity which necessitates the use of empirical rate equations. One such empirical rate expression for the auto-catalytic initiation reaction for the anionic polymerization of styrene in benzene solvent as reported by Tanlak (14) is given by ... 

The fairly broad most probable distribution for the rays may be considered as an undesirable imperfection of regular stars. Corresponding measurements with much narrower arm length distributions were made later, mainly by the research groups of Fetters [20, 30, 31] and Roovers [25, 26] which were obtained by living anionic polymerization of styrene, isoprene and butadiene respective-... 

In an all-glass reactor, a SAM of 4, 4-bromo-mercaptobiphenyls on Au(lll) surfaces was converted to biphenyUithium moieties by treatment with seoBuIi to initiate anionic polymerization of styrene on gold substrates (Fig. 9.24). 

Starting from 1956, living ionic polymerizations became the major interest for the synthesis of well-defined polymers. Szwarc reported that in the anionic polymerization of styrene (St) the polymer chains grew until all the monomer was consumed the chains continued to grow upon addition of more monomer [16],... 

Table 1 Values of the activation energy reported in the literature for the propagation reaction of the anionic polymerization of styrene (St) in different solvents...

Auguste S, Edwards HGM, Johnson AF et al. (1996) Anionic polymerization of styrene and butadiene initiated by n-butyllithium in ethylbenzene determination of the propagation rate constants using Raman spectroscopy and gel permeation chromatography. Polymer 37 3665-3673... 

Wang GM, van Beylen M (2003) Influence of 7t-complexing agents on the anionic polymerization of styrene with lithium as counterion in cyclohexane. 1. Effect of durene. Polymer 44 6205-6210... 

TABLE 5-11 Effect of Counterion on Anionic Polymerization of Styrene" ... 

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 case of work on phenylhthium anionic initiators, the first reported work by Jordan et al. involved the use of a SAM of biphenyllithium moieties on gold substrates to initiate anionic polymerization of styrene [26]. The thickness of the resulting dry polystyrene brush, as estimated by ellipsometry... 

The anionic polymerization of styrene using the organolithium initiators can be described as a termination-free polymerization, as shown in Eqs. (1)... 

Although the living nature of anionic polymerization of styrene testifies to the relative stability of the carbanion at the chain end, observations indicate that it may undergo spontaneous transformations.182 Polystyryl sodium in THF was shown to undergo termination involving hydride elimination followed by proton transfer ... 

As was stated above, the interpretation that the field affects the dis-sodation state of the growing chain ends was not uniquely substantiated by the experimental data, except those on copolymerizations. Thus it is interesting to investigate the field influence on much simpler systems than cationic homopolymerizations. For this purpose we have chosen living anionic systems in which only propagation steps are involved. The system first studied was a living anionic polymerization of styrene with n-butyllithium in the binary mixtures of benzene and tetrahydrofuran (17,24) and in the binary mixtures of benzene and dimethoxyethane (15). 

Table 3. Field effect on the living anionic polymerization of styrene in benzene-di-...

Ise, N., H. Hirohara, T. Makino, K. Takaya, and M. Nakayama Ionic polymerization under an electric field. XIII. living anionic polymerization of styrene in the Unary mixtures of benzene and dimethoxyethane by the three-state mechanism. Presented at the 17th Discussion Meeting of High Polymers, October, 1968, Matsuyama, Preprint p. 261. 

The anionic polymerization of styrene to produce stereoregular polymers has been studied by Kern and co-workers (23). They found that the polymerization of styrene by n-amylsodium at low temperatures produced crystalline polystyrene. Braun, HerNER and Kern (24) reported also that the potassium polymerization of styrene produced polymers with increased crystallinity as the temperature was decreased. 

These results are summarized in Fig. 5. With the anionic polymerization of styrene a balance of interaction between the propagating anion and the gegen ion is required. The ionic requirements for this balance... 

A comparison of Figs. 5 and 6 shows that between the anionic polymerization of styrene and the transition metal polymerization of styrene there is a region of poor catalysts which produce either atactic or no polymers. It has been shown by the substitution effects of the reaction that both the styryl anion and the styryl cation propagate on the... 

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. 

The catalysts which are required for the polymerization of butadiene to the 1.2 structure are less anionic than those for the anionic polymerization of styrene. The relative rates of the copolymerization of butadiene and of styrene is dependent on this anionic requirement of the propagating ion. Butadiene is polymerized to the near exclusion of... 

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