Group 4 complexes bearing bis(salphen) ligands: Synthesis,characterization, and polymerization studies

Six different complexes containing bis(salphen) [salphen = N,N'‐phenylenebis(salicylideneimine)] ligands were synthesized and characterized by various spectroscopic techniques and elemental analysis. In the presence of benzyl alcohol as an initiator, all the complexes catalyze the ring‐opening polymerization of lactide and ε‐caprolactone, generating high molecular weight (M_n) polymers in a controlled fashion. The linear relationship between the % conversion and M_n proved the control over the polymerization process. The presence of OBn group as an end group was confirmed by MALDI‐TOF and ¹H NMR spectral analysis of low M_n oligomers. The polymerization followed first‐order kinetics as revealed by kinetic experiments. All the complexes were good precatalysts for the polymerization of ethylene. The effect of temperature and time on the yield and activity toward the polymerization of ethylene were widely investigated. In addition, in the presence of tetrabutylammonium bromide as cocatalyst, the formation of degradable polycarbonate with moderate M_n value and narrow molecular weight distributions was observed by the copolymerization of cyclohexene oxide with CO₂. The effect of initiator structure, temperature, CO₂ pressure, catalyst/cocatalyst loading on the activity, and selectivity toward copolymerization were systematically examined. The thermal properties of the copolymer synthesized were explored using differential scanning calorimetric and thermogravimetric analysis. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 809–824