Polylactide is one of the most promising environmental friendly biopolymers due to its biodegradability and can be directly synthesized from renewable resources. The most efficient method to synthesize polylactide is the ring-opening polymerization (ROP) of lactide using the single-site homogeneous catalyst. The aim of this work is to synthesize titanium complexes supported by pyrrolylaldiminate ligands as initiators for the ROP of rac-lactide. The pyrrolylaldiminate (HL1−HL7) ligands were prepared by the reaction between pyrrole-2-carboxaldehyde with an equimolar amount of the corresponding primary amines. Treatment of the appropriate ligands with titanium(IV) isopropoxide in the molar ratio of 2:1 afforded titanium complexes (1−7) in moderate to good yields. All ligands and titanium complexes were characterized by 1H NMR, 13C NMR and elemental analysis. The polymerizations were carried out in toluene at 70 and 100 °C and the results revealed that all complexes were active initiators for the ROP of rac-lactide. The molecular weights of the resulting polymers were in closed agreement with the theoretical values and the PDI values were narrow. The results from the homonuclear decoupled 1H NMR spectroscopy analysis demonstrated that the microstructures of polylactides produced by all complexes were atactic. In addition, the electronic and steric effects from ligand substituents were found to have a significant impact on the polymerization activity.

Controlled ring-opening polymerization of rac-lactide by titanium complexes

2019 Spring National Meeting

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