A new class of salicylaldiminato tin(II) catalysts having different alkoxy side chains has been developed. The ligands were modified to have different lengths and flexibilities such as –(CH2)2– (2a), –(CH2)3– (2b), –(ortho-C6H4)CH2– (2c) and –(CH2)2–O–(CH2)2– (2d). Complexes 2a, b were characterized crystallographically revealing a more constrained environment around the metal in complex 2a. These catalysts are active for the solvent-free polymerization of L-lactide and ε-caprolactone. Complex 2a having a shorter side chain was shown to better promote intramolecular transesterification affording cyclic polylactides and cyclic poly(ε-caprolactone). Complexes 2b and 2d having longer side chains produced cyclic poly(ε-caprolactone) as a major product but failed to give cyclic polylactides.

The ring-opening copolymerization (ROCOP) of epoxides and cyclic anhydrides is a promising method for the synthesis of new polyesters with various polymer properties. Among previously reported metal catalysts for ROCOP, the Schiff-base complexes have gained significant attention because of their ease of synthesis and modification. In this work, zinc and magnesium complexes containing Schiff-base ligands with different alkoxy side arms [−(CH2)2O– and −(CH2)3O−] were synthesized and shown to have a cubane metal core by X-ray crystal structures. All complexes were studied in the ROCOP of cyclohexene oxide (CHO) and succinic anhydride (SA) in toluene at 110 °C. The zinc complex having a shorter side arm is the most active catalyst for copolymerization, giving poly­(CHO-alt-SA) with narrow dispersity and negligible ether linkage. On the other hand, magnesium complexes were not active because of the formation of stable carboxylate species. The detailed analysis of polyester obtained from zinc complexes unexpectedly revealed three different types of polymer structures occurring at different polymerization times. Cyclic polymer was generated at the beginning by intramolecular transesterification of the alkoxy side arm, giving a low-molecular-weight polyester. At higher conversion, cyclization diminished, giving just a linear polyester but with minor competitive formation of higher-molecular-weight polyester having cyclohexanediol as an end group. On the basis of a thorough understanding of the polymerization mechanism, the desired cyclic poly­(CHO-alt-SA) was successfully synthesized using a low monomer/catalyst ratio.

Tin(ii) complexes suported by guanidinate ligands have been synthesized and shown to polymerize lactide and ε-caprolactone to cyclic polyesters.

A series of two reactors is commonly used to produce commercial polypropylene resins to make products with a broad range of microstructures using different feeding policies and/or operating conditions in both reactors. A mathematical model describing the molecular weight distribution (MWD) and yield of polypropylene made with a Ziegler-Natta catalyst in a two-reactor system is developed in this work. A new methodology to estimate the polymerization kinetic parameters combining the simultaneous MWD deconvolution and analysis of polymer yields in both reactors is also proposed. This pragmatic approach can be applied without knowledge of detailed polymerization rates and is, therefore, very convenient to quantify polymerizations in continuous pilot and/or commercial reactors, where such information is generally not available.