Block Copolymer Formation by Transformation Reactions

Abstract

The ring-opening polymerisation of cyclopentene catalysed by the premixed and unmixed bimetallic catalyst system WCl₆/LiBu has been studied dilatometrically. These studies show that both the premixed and unmixed catalyst systems show similar catalytic properties. The rate of polymerisation shows a maximum at a catalyst/monomer ageing time of less than 20 minutes, which is roughly comparable to the results obtained for the polymerisation of cyclopentene catalysed by WCl₆/Al(iBu). The rate of polymerisation increases with increasing monomer or tungsten concentration but the rate falls dramatically to zero after 8 minutes reaction time at high monomer (and possibly catalyst) concentrations. Also, as the cocatalyst concentration increases, the initial rate of polymerisation appears to increase accordingly but, after a few minutes, the reactions performed at high cocatalyst concentrations fall and the rate of polymerisation appears to show a maximum at a W:Li molar ratio of 1:2. Studies on the polymerisation of cyclopentene catalysed by WCl₆/PSt-Li show that the resultant products contain copolymers of polycyclopentene/polystyrene and therefore demonstrate the importance of the role played by the cocatalyst in metathesis reactions. Model compound studies suggest that the metallocarbene initiator is formed by an alpha hydrogen migration from the cocatalyst to the transition metal catalyst; the reaction is believed to be covalent rather than ionic. Work performed at PERME Waltham Abbey has shown the possibility of synthesising substituted amines of the form RN, where R = poly(tetramethylene oxide) and x = 1, 2 or 3. The yield of the trisubstituted amine may be dramatically increased by performing the reaction in the presence of a proton sponge.