A new sodium/potassium crown ether complex system with a series of bichelating sulfonamides as ligands was developed for the ring-opening polymerization (ROP) of rac-lactide. In this system, the side reaction of cyclic polymerization can be suppressed very well because of very different ROP rates initiated by BnOH and sulfonamide anion. The synthesis of high molecular weight linear polylactide with molecular weight high up to 107 kg/mol was successful. The best isoselectivity also can reach to a high value of P m = 0.84. The NMR analysis of the reaction mixture of rac-lactide and complex 3 together with kinetic studies suggests the mechanism of ROP in the absence of alcohol is a coordination–insertion mechanism. After addition of BnOH, the ROP rate can increase remarkably due to the cooperation interaction of alcohol and complex 3.

Synthesizing different types of sequence-controlled copolyesters can enrich the diversity of copolyesters and modify their properties more precisely, but it is still a challenge to synthesize a complicated sequence-controlled copolyester using different hydroxy acids in a living polymerization manner. In this work, a highly regioselective and stereoselective catalytic system was developed to synthesize biorenewable and biodegradable copolyesters of mandelic acid and lactic acid with isotactic-alternating, heterotactic-alternating, and ABAA-type precise and complicated sequences. Because of the regular incorporation of mandelic acid into polylactide, these sequence-controlled copolymers of mandelic acid and lactic acid show higher glass-transition temperatures than polylactide and a random copolymer. A stereocomplexation interaction between two opposite enantiomeric isotactic polymer chains was also discovered in the isotactic-alternating copolymer.

Ring-opening polymerization (ROP) of rac-Ocarboxyanhydride of mandelic acid (rac-manOCA) is a promising method to synthesize isotactic biodegradable polyester of poly-(mandelic acid), which has a high glass-transition temperature (T g ) and a high melting temperature (T m ) due to the formation of a stereocomplex. However, it is still a big challenge to synthesize isotactic poly(rac-manOCA) so far because of the easy epimerization of manOCA in the polymerization progress. In this work, a highly isoselective ROP of the rac-manOCA system as the first stereoselective example is reported using weak Lewis pairs of zinc complexes and 3-fluoropyridine (3-F-Py) as catalysts with the highest P m value of 0.92, and no obvious epimerization happens in the polymerization progress. T g of poly(rac-manOCA) (∼5.3 kg/ mol) increases from 84 to 92 °C when the isotacticity increases from P m = 0.60 to 0.92. Isothermally crystallized isotactic poly(rac-manOCA) (5.3 kg/mol, P m = 0.92) demonstrates a melting point at 116 °C, and no obvious melting point can be found for the almost atactic poly(rac-manOCA) (5.4 kg/mol, P m = 0.60). The T m value of a 1:1 mixture of enantiopure poly(L-manOCA) and poly(D-manOCA) can reach 173 °C after isothermal crystallization.

The reactivity of a catalytic polymerization system using photoresponsive azobenzene-based thiourea/PMDETA as a catalyst could be switched between slow and fast states by alternating exposure to UV and ambient light, because the active site of azobenzene thiourea is blocked via intramolecular hydrogen bonding when the azobenzene thiourea transfers from the E isomer to the Z isomer under UV irradiation.

Three potassium crown ether complexes supported with bulky amidinate ligands were synthesized for the ring-opening polymerization (ROP) of rac-lactide. The side polymerization reaction initiated directly by ligand anion was suppressed well in the presence of alcohol as our design, and the synthesis of linear polylactide with a molecular weight as high as 117.7 kg/mol was successful together with an isoselectivity value of P = 0.88 at -70 °C. In this system, lactide can be deprotonated by amidinate anion to give lactide enolate, which can initiate the ROP of lactide as a side reaction in the absence of alcohol; however, this side reaction can also be suppressed well in the presence of alcohol by a decrease in temperature. An interesting anti-Arrhenius-like behavior in the polymerization was discovered, which can be attributed to the fact that the active catalyst can be converted to a less active lactide enolate potassium complex at a high temperature.