The influence of the metal (Al, Cr and Co) and the substituents of the porphyrin in controlling the reactions involved in the copolymerization of propylene oxide and cyclic anhydrides by porphyrin metal(III) complexes

A series of porphyrin metal(III) complexes of general formula LMX (L = tetraphenylporphyrin (TPP), octaethylporphyrin (OEP), tetrakispentafluorophenylporphyrin (TFPP), M = Al, Cr, Co, X = Cl, OH or OEt); has been investigated as catalyst systems for the copolymerization of propylene oxide (PO) and cyclic anhydrides to produce polypropylene carboxylates, with and without a Lewis base cocatalyst: bis(triphenylphosphine)iminium chloride (PPN+Cl−). The highest rate of copolymerization was observed with 1.0 equiv. cocatalyst and the use of phthalic anhydride (PA) monomer allowed the formation of higher molecular weight polyesters. The terpolymerization of PO, cyclic anhydride and CO2 produced poly(ester-b-carbonates). With PPN+Cl− cocatalyst, TPPCrCl catalyst system produced two polymer chains per metal. The polymerization processes were followed by 1H NMR spectroscopy and polymer samples were characterized by GPC, Mass (ESI and MALDI TOF) and NMR (1H, 13C{1H}) spectroscopy. The observed results are compared with earlier studies of salen and related complexes.