Copolymers with Cyclo-olefins

Amongst copolymers of PE, there are polyallomers (ethylene-propylene copolymers), copolymers with cyclo-olefins and with vinylic monomers [with vinyl acetate ethylene-vinyl acetate, (EVA), with methacrylic acid, MA, and with vinyl alcohol ethylene - vinyl alcohol, (EVOH)], and chlorinated PE (CPE). CPE, although it exhibits exceptional UV and chemical resistance, gives rise to a high amount of hydrogen chloride gas evolution if combusted. 

Ethylene-cyclo-olefin copolymers have been known since 1954 (DuPont USP2 721 189) but these materials only became of importance in the late 1990s with the development of copolymers of ethylene and 2-norbomene by Hoechst and Mitsui using metallocene technology developed by Hoechst. The product is marketed as Topas by Ticona. By adjustment of the monomer ratios polymers with a wide range of Tg values may be obtained including materials that are of potential interest as thermoplastic elastomers. This section considers only thermoplastic materials, cyclo-olefins of interest as elastomers are considered further in Section 11.10. 

In this section wc consider systems where the radical formed by propagation can eyclizc to yield a new propagating radical. Certain 1,4-dicncs undergo cyclocopolymerization with suitable olefins. For example, divinyl ether and MAH are proposed to undergo alternating copolymerization as illustrated in Scheme 4.19.167 These cyclo-copolymerizations can he quantitative only for the case of a strictly alternating copolymer. This can be achieved with certain electron donor-electron acceptor pairs, for example divinyl ether-maleic anhydride. 

Metallocenes were developed by Kaminsky and Sinn [42] by developing a new activator. Since then, metallocene technology has progressively undergone changes and has removed the carpet from under ZN catalysts. It is a mature technology now and more than 4 billion dollars has been spent in their development (Table 15). Syndiotactic PP, cyclo-olefin copolymers, and polar monomer incorporation are possible with metallocenes. 

Here, we review (1) research activities in metallocene catalysts, (2) polymerization performances of metallocene catalysts and other single-site catalyst technologies, with examples for polyethylene (PE), cyclo-olefin copolymer (COC), polypropylene (PP), syndiotactic polystyrene (SPS), and cyclo-olefin polymers, and (3) the computational design of metallocene catalysts. 

Metallocene catalysts have a unique feature of polymerizing cyclo-olefin monomers (i.e., cyclopentene, norbornene) selectively without ring opening, and also enable copolymerization with ethylene [47, 48]. Application of metallocene catalysts to cyclo-olefin copolymer (COC) will be discussed in Section IV. 

Figure 3.1 (a) Distribution of molecular weights for ethylene-propylene copolymers from isospecific metallocenes (b) gel permeation chromatography elution curves for HDPE produced with CpTiPhj and Cp ZrCl mixtures. Cp = cyclo-olefins [23]... 

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