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Copolymerization studies of ethylene and trimethylsilyl protected 1-alkenols using a Brookhart-type alpha-diimine nickel(II) dibromide precatalyst
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There has been considerable interest over the past decade in the preparation and applications of copolymers of ethylene with functionalized polar olefins. Such copolymers are expected to exhibit a variety of potentially very useful properties such as paintability, adhesion to polar surfaces, and miscibility with polar polymers such as polyesters and polyamides, but there are limitations associated with producing copolymers of ethylene with polar monomers via Ziegler-Natta processes. Many classes of Ziegler-Natta catalysts, especially those of the early transition metals (Ti and Zr), are highly oxophilic and hence are poisoned by functionalities such as -OH groups. This problem can in principle be alleviated by implementing the use of protecting groups such as –OSiMe3, which has previously been shown to be an effective masking agent both for steric reasons and because O-Si π bonding decreases the Lewis basicity of the ether oxygen atom. One can also utilize late transition metal catalyst systems, which are generally less Lewis acidic and therefore less susceptible to poisoning by functional groups. In this thesis the results of an investigation of the copolymerization of ethylene with CH2=CH(CH2)nOSiMe3 (n = 1, 2, 8) will be presented. We have been using MAO activated dibromo[1,4-bis(2,6-diisopropylphenyl)acenaphthenediimine]nickel(II) (D) as catalyst, as this system is known to produce reasonably linear polyethylene and hence may be expected to produce essentially LLDPE containing –(CH2)nOSiMe3 branches. The latter can be hydrolyzed to give polar –(CH2)nOH branches.