Coordination polymerization styrene

First, new "living" initiators have been discovered (although not always as efficient), which respond to other mechanisms, i.e. cationic (5) or even radical ones (6), and can accordingly accomodate other types of monomers. A recent typical example is the coordination polymerization of butadiene by bis (n3-allyl-trifluoro-acetato-nickel) to yield a "living" pure 1.4 cis-poly-butadienyl-nickel, able to initiate in turn the polymerization of monomers like isoprene or styrene (7). 

The radical model cannot be applied for ionic and coordination polymerizations. With a few exceptions, termination by mutual combination of active centres does not occur. The only possibility is to measure the rate of each copolymerization independently. The situation can be greatly simplified for copolymerizations in living systems. The constants ku and k22 can usually be measured easily in homopolymerizations. Also, the coaddition constants fc12 or k2] are often directly accessible when the M] and M2 active centres can be differentiated spectroscopically or when the rate of monomer M2 (M[) consumption at M] M 2 centres can be measured. Ionic equibria, association, polarity of medium and solvation must be respected, even when their quantitative effect is not known exactly. The unusual situations confronting macromolecular chemistry will be demonstrated by the example of the anionic copolymerization of styrene with butadiene initiated by lithium alkyls in hydrocarbon medium. 

We assumed that the polymerization proceeds by a normal coordination polymerization. The effect of the catalyst concentration on the polymerization was examined by polymerization at different ratios of catalyst to styrene (Figure 17.13). The reaction rate increased in proportion to the catalyst ratio. However, the decay of the polymerization reaction was too fast to explain it as a first-order reaction. 

The first attempt to imprint a metal complex with a reaction intermediate coordinated to the metal center was reported by Mosbach and coworkers [51], A Co monomer coordinated with dibenzoylmethane, which is as an intermediate for the aldol condensation of acetophenone and benzaldehyde, was tethered to a styrene-DVB copolymer matrix. After, the template, dibenzoylmethane was removed from the polymer, the resulting molecularly imprinted cavity had a shape similar to the template due to the interaction of the template with the polymerized styrene-DVB monomers through n-n stacking and van der Waals interactions. The rate of aldol condensation of adamantyl methyl ketone and 9-acetylanthracene was lower than the rate of condensation with acetophenone, indicating some degree of increased substrate selectivity. This is the first known formation of a C-C bond using a molecularly imprinted catalytic material. 

Cp2TiMe2 is activated by various borate salts to give catalytic systems for the polymerization of ethylene, propylene, and styrene. A conventional Ziegler-Natta coordination polymerization mechanism is proposed for ethylene and propylene polymerization, while a carbocationic polymerization mechanism has been suggested for styrene.1497... 

New block copolymers of polystyrene and poly(e-caprolactone) have recently been prepared with a combination of coordination catalyst and anionic polymerization( An amorphous styrene block was prepared by conventional anionic polymerization at room temperature, and terminated with ethylene oxide. After hydrolysis the terminal - OH groups were substituted by oxo-Al-Zn alkoxide. A crystalline block was then added by coordination polymerization of e-caprolactam. 

Silylene 1 is an unusually versatile catalyst for alkene and alkyne polymerization. The list of compounds polymerized by 1 includes ethene, propene, 1-hexene, styrene, dimethylbutadiene, vinylidene chloride, vinyl ethyl ether, methyl methacrylate, and phenylacetylene. The polymerization does not seem to take place by any of the usual mechanisms, anionic, cationic or free-radical. Instead it somewhat resembles coordination polymerization, as observed for Ziegler-Natta type catalysts. Silylene 2 also catalyzes the polymerization of 1-hexene, but the polymerization is 10 to 100 times slower than with 1. 

Proto et al. [434] living isoselective coordination polymerization of styrene to form isoselective block copolymers. This was accomplished by sequential monomer addition. 

Recently, Baird and co-workers have reported (75) examples of polymerizations by a simple mono-Cp titanium complex, (C5(CH3)5)Ti(CH3)3 activated with a Lewis acid (B(C6F5)3) that not only copolymerizes ethylene and a-olefins but also induces polymerization of monomers normally associated with cationic polymerization such as isobutylene and vinyl ethers. Shaffer and Ashbaugh foimd (76) that for isobutylene and a-methylstyrene, the metal complex is an initiator rather than a catalyst (if it even participates at all), but that a transition from cationic to coordination polymerization occurs in styrene polymerization as temperature is raised. Even if it merely functions as an initiator, however, these investigations have revealed new polymerization systems based on anions such as [RB(C6F5)3l (R = alkyl, CeFs) that are less prone to side reactions tending to limit the MW and degree of polymerization of monomers like isobutylene at moderate temperatures (T > -80°C). 

Deactivation. One of the factors that complicates the quantification of active-site concentration (135) is the fact that metallocene cations are subject to equilibria between catalytically active and inactive forms. In situations in which intramolecular coordination of an arene group can occur, this process competes with monomer coordination in styrene (136) and possibly olefin polymerization. Another dormant state invoked to explain catalyst decay is the dimeric structure [Cp2Zr(CH3)(/u.-CH3)Zr(CH3)Cp2]+ in which a methyl group bridges two metallocene fragments. This has been characterized by NMR for the reaction of Cp2Zr( CH3)2 with MAO and other cocatalysts (136). 

The syndiotacticity of sPS resnlts from the homogeneons coordinative polymerization process (1,42). Styrene monomer complexes at a vacant coordination site on the transition metal, typically titanium, and inserts into a titanium carbon or hydride bond (Fig. 5). In the case of the growing polsrmer chain, the insertion occurs via cis-addition with secondary insertion so that the titaniiun is attached to the carbon bearing the phenyl substituent (43). Chain transfer occurs typically via -hydride elimination, forming a titanium hydride, or via reaction with an... 

Wang, Q. Quyoum, R. Gillis, D. J. Tudoret, M.-J. Jeremic, D. Hunter, B. K. Baird, M. C. Ethylene, styrene, and a-methylstyrene polymerization by mono(pentamethylcyclopentadienyl) (Cp ) complexes of titanium, zirconium, and hafnium Roles of cationic complexes of the type [Cp MR2] (R = alkyl) as both coordination polymerization catalysts and carbocationic polymerization initiators. Organometallics 1996,15, 693-703. 

Transition metal complexes functioning as redox catalysts are perhaps the most important components of an ATRP system. (It is, however, possible that some catalytic systems reported for ATRP may lead not only to formation of free radical polymer chains but also to ionic and/or coordination polymerization.) As mentioned previously, the transition metal center of the catalyst should undergo an electron transfer reaction coupled with halogen abstraction and accompanied by expansion of the coordination sphere. In addition, to induce a controlled polymerization process, the oxidized transition metal should rapidly deactivate the propagating polymer chains to form dormant species (Fig. 11.16). The ideal catalyst for ATRP should be highly selective for atom transfer, should not participate in other reactions, and should deactivate extremely fast with diffusion-controlled rate constants. Finther, it should have easily tunable activation rate constants to meet sped c requirements for ATRP monomers. For example, very active catalysts with equilibrium constants K > 10 for styrenes and acrylates are not suitable for methacrylates. 

Polystyrene is imusual among commodity polymers in that we can prepare it in a variety of forms by a diversity of polymerization methods in several types of reaction vessel. Polystyrene may be atactic, isotactic, or syndiotactic. Polymerization methods include free radical, cationic, anionic, and coordination catalysis. Manufacturing processes include bulk, solution, suspension, and emulsion polymerization. We manufacture random copolymers by copolymerizing styrene directly vith comonomers containing vinyl groups. In addition, we can polymerize styrene in the presence of polymer chains containing unsaturation in order to create block copolymers. Crosslinked varieties of polystyrene can be produced by copolymerizing styrene vith difunctional monomers, such as divinyl benzene. 

The structure of the dormant sites might be an irregular coordination of the monomer (Rg. 4.10b) or a change of the direction of the monomer coordination (Rg. 4.10c). Tlie polymerization reaction may be stopped after an irregular coordination of styrene. This also supports the chain-end controlled mechanism of stereospecilicity. 

Schellenberg, J. Effect of impurities on the syndiospecific coordination polymerization of styrene. Macromol. Mater. Eng., 290,833-842 (2005). 

The Introduction gives a historical overview of SPS from the first discovery through developmental stages to the fuU commercialization of this polymer based on an inexpensive monomer (Chapter 1). Because the transition metal catalysts for the coordination polymerization of styrene are of high importance for the properties of the polymers, these catalysts are comprehensively covered in the section on the preparation of SPS. 

As with iron(II), O Reilly et reported that nickel complexes with an a-diimine ligand (Ni-9), which is an analog of the precursor for a coordination polymerization catalyst, efficiently worked for controlling the radical polymerization of styrene. When coupled with 1-phenylethyl bromide as the initiator, the styrene polymerization with Ni-9 provided well-controlled molecular weights and MWDs (Mw/Mn= 1.15). Neutral Ni(II) acetylides (Ni-10 and Ni-11) were used for the polymerization of DMAEMA and MMA in conjunction with an organic halide as the initiator by Sun et Although judicious conditions, such as concentra-... 

Industrialization of coordination polymerization of styrene using metallocenes and leading to syndiotactic polystyrene is in progress. 

TABLE 8.10 Effect of Catalyst on the Course of the Coordination Polymerization of Styrene and Propylene at Temperature of 313 K... 

Polystyrene is one of the most important commodity polymers and perhaps the most well-known and most extensively studied polymers. Styrene can be polymerized by free-radical polymerization, ionic (cationic and anionic) polymerization, and coordination polymerization. Free-radical polymerization is most frequently used to produce atactic polystyrene. Ionic polymerization is used to prepare polystyrene of narrow molecular-weight distribution. Because styrene reacts readily with many other vinyl monomers and rubbers, a wide variety of styrene copolymers are commercially available. There are many styrene copolymers commercially available, but the following four styrene polymers are of particular importance ... 

---