Ethylene/styrene copolymerization using systems

ETHYLENE/STYRENE COPOLYMERIZATION USING TRANSITION METAL COMPLEX-COCATALYST SYSTEMS... 

TABLE 5.10 Ethylene/Styrene Copolymerization Using Dichloro l,4-dithiabntanediyl-2,2 -bis(4,6-di-tert-bntylphenoxy) Titaninm Complex (20)-MAO Catalyst System[46] ... 

Although ordinary metallocenes are inactive for styrene polymerization, certain metallocenes can be effective for ethylene/styrene copolymerization [20-23]. Oliva et al. reported that the regiospecificity of styrene insertion into the Zr- CHs bonds is predominantly secondary in ethylene/styrene copolymerization using the [Me(Ph)C(fluorenyl)(Cp)]ZrCl2-MAO catalyst system [20]. Oliva later presented that some styrene units can be introduced in an isotactic polypropylene sequence (1,2-insertion) by using a small amount of ethylene to reactivate the catalyst after the styrene insertion (2,1-insertion) in propylene/styrene copolymerization using a r c-[Et(indenyl)2]ZrCl2-MAO catalyst system [21]. 

The less nucleophilic acetals copolymerize with vinyl compounds more readily. Perhaps, in these systems the alkoxycarbenium ions (... —OCH ) that coexist in equilibrium with oxonium ions facilitate copolymerization with vinyl compounds. Styrene copolymerizes with trioxane 51,52) and tetraoxane53). The latter system yields polytrioxane and trioxane-styrene copolymer together with 1,4-phenyl-1,3-dioxane. It was formed in 25% yield in ethylene dichloride at 30 °C after 1 hr using [BF3 OEtj] = 10-2 mol l-1, [styrene], = [tetraoxane = 0.5 mol l-1. The proposed mechanism of 4-phenyl- 1,3-dioxane formation is shown below (cf. also Chap. 7) ... 

Styrene incorporation in ethylene/styrene dramatically improved with the use of a dinuclear catalyst system (Ti22Bi), and a copolymer with a high styrene content (76mol %) has been synthesized with this catalysis (Table 5.5). Therefore, this catalyst system afforded broad-range controllable styrene incorporation (styrene contents 39-76mol %) in copolymerization, although the observed activities should be further improved [19a]. Resonances ascribed to the three consecutive head-to-tail coupled styrene units in addition to tail-to-tail coupled dyads were observed in the NMR spectra of the resultant copolymers (styrene >50 mol %) [19a]. They assumed that the arene ring of the last-inserted styrene may preferentially coordinate with the adjacent Ti... 

Ziegler-Natta, Phillips, and metallocene catalysts are extensively used to produce polyolefins by catalytic polymerization. These catalysts allow a good control of polymer microstmctiue and large productivities, but they are based on early transition metals (Ti, Zr, Cr, and V), which are oxophilic, and hence sensitive to water. Therefore, they cannot be used in aqueous systems although some relative success has been recently repotted in the polymerization of styrene with metallocene catalysts. Late transition metals (Rrr, Co, Rh, Ni, and Pd) are much less oxophilic, and hence they may be used in water systems. In the past 30 years, a great deal of work has been done to develop late transition metal catalyst to polymerize ethylene and copolymerize it with acrylates in both solvent and aqueous phases. ° Tfre neutral nickel complexes of [P,0]... 

Some data recently obtained on high pressure ethylene copolymerizations illustrate the quantitative aspects of an ethylene-based Q-e scheme (6). In Figures 3 and 4 copolymer composition curves for the ethylene-vinyl chloride and the ethylene-vinyl acetate copolymerizations are given. The monomer reactivity ratios for these two systems are tabulated in Table III along with Q values and e values for vinyl chloride and vinyl acetate calculated using ethylene as the standard (Q = 1.0 and g = 0). These Q and e values may be compared with those obtained using styrene as the standard. 

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