A recent study has been directed to the design of metal-free Lewis pair catalysts for ring-opening alternating copolymerization (ROAP) reactions to enhance both activity and selectivity. While the simplest types of organic bases/Lewis bases (for example: PPN⁺Cl⁻, DMAP, DBU and TBD) are able to copolymerize anhydride-epoxide in a non-living and non-quantitative manner, the introduction of Lewis acids radically changes this behaviour. In this study, various Lewis acids such as B(C₂H₅)₃, Al(CH)₃, Et₂Zn and ⁿBu₂Mg in combination with various Lewis bases such as PPN⁺Cl⁻, DMAP, DBU and TBD were tested as Lewis pair catalysts for anhydride-epoxide ring-opening copolymerization (ROCOP) studies. Based on the observed results, the B(C₂H₅)₃/PPNCl pair stood out as the most active and effective Lewis pair for the perfectly alternating and regioselective controlled ROCOP of various epoxides (cyclohexene oxide, CHO; tert-butyl glycidyl ether, tBGE and 2-benzyloxirane, BO) with phthalic anhydride (PA). Medium to high molecular weight linear poly(anhydride-co-epoxide)s (M_n up to 57.5 kg mol⁻¹) are achieved, and most of them exhibit narrow molecular weight distributions (M_w/M_n as low as 1.07). However, in the presence of strong Lewis acids (Al(CH)₃, Et₂Zn and ⁿBu₂Mg) and neutral Lewis bases (DMAP/DBU/TBD) this broad applicability is offset by the lack of control over the polymerizations, including the side reactions as a consequence of strong acidity/alkalinity. Hence, the ideally suitable acidity/alkalinity and matched size of the Lewis pair are considered crucial for the effective copolymerization of PA and epoxides. In addition, from P(PA-alt-tBGE) copolymers, hydroxyl-functionalized poly(ester-alt-glycerol)s were successfully synthesized by deprotection of the t-butyl groups.

A complete library of new alkoxides containing group 4 metals and the imino phenol ligand were synthesized in high yields and purity. These compounds showed catalytic activity towards the polymerization of L-lactide (L-LA), rac-lactide (rac-LA), ε-caprolactone (CL), δ-valerolactone (VL), rac-β-butyrolactone (rac-BL), ethylene and propylene. The zirconium catalysts were found to yield better polymerization results in comparison to the titanium and hafnium analogues. The number average molecular weight (M_n) values of the polymers are very high for LA and CL with controlled molecular weight distributions (MWDs). Analyses of MALDI-TOF and ¹H NMR spectra of low M_n oligomers reveal that the ligand initiates the ring-opening polymerization (ROP). For ethylene and propylene polymerization, we have achieved moderate to good activity using MAO as a co-catalyst.