Tetraphenylporphyrin-aluminium compounds as initiators for the ring-opening polymerization of 2,2-dimethyltrimethylene carbonate: synthesis of homopolymers and copolymers with ε-caprolactone, ethylene oxide and propylene oxide

Abstract

Insertion polymerization of 2,2-dimethyltrimethylene carbonate (DTC) with initiators based on tetraphenylporphyrin-aluminium (TPPAl-R) results in high yields of poly (2,2-dimethyltrimethylene carbonate) without cyclic oligomers being formed. This indicates that back biting does not take place. The polymerization reaction is slow in methylene chloride or toluene at room temperature; the reaction rate increases with increasing temperature. Tetraphenylporphyrin-alkoxides (TPPAl-OR), the most active initiators for DTC polymerization, from a mixture of DTC and ε-caprolactone (ECL) yield a statistical copolymer, indicating poor selectivity towards these monomers. The initiator, however, is well suited for block copolymer synthesis upon stepwise addition of the monomers, e.g. poly (ECL- block-DTC), poly (ethylene oxide- block-DTC) and poly (propylene oxide- block-DTC). The thermal properties of poly (propylene oxide- block-DTC) as a function of composition are reported. Copolymers with a high propylene oxide content show a pronounced glass transition temperature for the polyether block; all copolymers show only one melting transition which is assigned to that of the polycarbonate block.