Semi-aromatic polyesters by alternating ring-opening copolymerisation of styrene oxide and anhydrides

Abstract

Ring-opening copolymerisation of styrene oxide with alicyclic anhydrides containing different ring strains (succinic anhydride, maleic anhydride, citraconic anhydride, cyclopropane-1,2-dicarboxylic acid anhydride, cyclopentane-1,2-dicarboxylic acid anhydride and phthalic anhydride) was performed applying metal salen and tetraphenyl porphyrin complexes where for (salen)MX, M = Cr, X = Cl (1), M = Al, X = Cl (2), M = Mn, X = Cl (3), M = Co, X = OAc (4) and salen = N,N-bis(3,5-di-tert-butylsalicylidene)-diimine and for porphyrin complex, M = Cr, X = Cl (5), M = Mn, X = Cl (6), M = Co, X = OAc (7). The chromium catalysts performed best and therefore 1 was chosen as the selected catalyst for further studies. Investigation of the effect of different cocatalysts on the copolymerisation of styrene oxide and phthalic anhydride revealed that phosphines and onium salt showed quite similar activities whereas N-heterocyclic based amines showed somewhat lower activity. 1H NMR and MALDI-ToF-MS spectra of the copolymers formed confirmed the alternating microstructures. Increasing the monomer to catalyst ratio resulted in the isomerisation of styrene oxide to phenyl ethanal. The aldehyde functions as a chain transfer agent influencing the molecular weight of the polymers. Copolymerisation of styrene oxide with anhydrides bearing a double bond in their structure, such as maleic anhydride and citraconic anhydride, was shown to be highly dependent on temperature, time, type of cocatalyst and solvent used in the copolymerisation reaction.