Aluminium triisopropoxide: An inexpensive and easy-to-handle catalyst of the copolymerisation of cyclohexene oxide with CO2

Aluminium triisopropoxide, a versatile and cheap oligomeric Lewis acid catalyst, easily reacts with carbon dioxide to build complex oligomeric aluminium alkoxo-alkylcarbonato compounds. A first series of experiments with cyclohexene oxide and CO2 showed that the catalyst is highly active in the copolymerisation with carbon dioxide and that a satisfactory carbon dioxide insertion takes place when the reaction is run at temperatures between 50 and 80 °C and pressures around 100 bar CO2. High yields of polyether-carbonates can be obtained (up to 1000 g of copolymer per g aluminium) with molecular weight up to 11 000 g mol−1 and a better selectivity of the CO2-insertion than other aluminium trialkoxides (carbonate to ether linkages ratio: 1 to 3). On the basis of 27Al-NMR spectra it can be seen that the high reactivity of the catalyst is due to a rearrangement of the stable tetrameric aluminium isopropoxide in a more reactive oligomer and, most likely, during the copolymerisation, to a further fragmentation into reactive monomeric species.