Abstract
Cyclopentadienyltitanium trichloride (OpTiCl3) is a convenient catalyst that, when activated by co-catalyst methylaluminoxane (MAO), has been shown to effect stereoselective polymerisation of styrene to yield syndiotactic polystyrene. However, it has not been used to polymerise polar, functionalised monomers such as methyl acrylate. In this thesis the CpTiCl3/MAO system was found to polymerise styrene to yield the polymer in low yield, although the syndiotacticity found by others was absent with the NMR evidence suggesting atactic polymer. However, the polar monomer methyl acrylate was found to polymerise readily under the same conditions to give rubbery polymer in good yield, which NMR indicated is probably heterotactic. The diene isoprene was found to give a very low yield of polymer, in keeping with some related dienes in the literature. For methyl acrylate, the Mw was up to 15,000, although the polydispersity was good at 1.92. Co-polymerisation of methyl acrylate/styrene, methyl acrylate/isoprene and styrene/isoprene were carried out. Only the co-polymer of methyl acrylate/styrene was obtained in good yield, but there is NMR evidence of a ca. 1:1 alternating co-polymer, which is alternating. In addition, scanning electron microscopy (SEM) showed evidence of a homogeneous morphology on a sub-micron scale indicating a true co-polymer as opposed to a blend of homopolymers. A kinetic study of the methyl acrylate homopolymerisation showed the reaction to be relatively rapid (k obs= 39.43 x 10e-6 s-1 at [MAO] = 53mM and [CpTiCl3] = 0.6mM), and exhibited saturation in [CpTiCl3] and [MAO] and linearity in [methyl acrylate]. The addition of a co-monomer, styrene, greatly slowed the reaction. The kinetic results are interpreted in terms of an enolate mechanism, with pre-binding of the monomer to an activated Ti species. In the case of methyl acrylate/styrene co-polymerisation the binding of the monomers alternates, leading to the alternating 1 : 1 co-polymer.