Bench‐stable potassium complexes for living and isoselective ring‐opening polymerization of rac‐lactide

Abstract

To develop bench‐stable and nontoxic catalysts for the ring‐opening polymerization (ROP) of lactides is of importance with the aim of reducing costs in industrial production. Although, recently, some potassium complexes have been reported for the living polymerization of rac‐lactide (rac‐LA), the moisture sensitivities of these complexes prevent their further applications in the mild polymerization condition. In this work, three bench‐stable potassium phenolates as isoselective catalysts for the ROP of rac‐LA were reported, and the moisture stability of these complexes does not inhibit their high activity under mild conditions even in the presence of trace water (2.0 equivalent relative to the catalysts) or unpurified solvents. The controllable polymerization reactions can afford polylactides with desirable molecular weights, which can be high up to Mn = 80.0 kg/mol at an anhydrous condition and Mn = 54.3 kg/mol in presence of trace water. A best isoselectivity of Pm = 0.83 also can be achieved in this system at −70°C.

Photoresponsive thiourea and urea catalysts for ring‐opening polymerization of L‐lactide

“…Interestingly, for the highly active catalyst C1 and C2, the ROP under exposure to 365 nm UV light led to a 0.5 to 2.6-fold increase in activity (Table 1, entries 1-10) compared with the ROP under exposure to visible light. In contrast, the ROP mediated by C3 or C4 in the presence of MeOK under exposure to 365 nm UV light led to decrease in activity (Table 1, entries [11][12][13][14][15][16][17][18][19][20][21][22]. The ROP mediated by C5 and MeOK under exposure to 365 nm UV light led to increase in activity (Table 1, entries [23][24][25][26][27][28].…”

“…6,7 Organocatalysts or the metal catalysts based on nontoxic Na and K have received much attention in the field of ROP. 6,[8][9][10][11][12][13][14][15][16][17][18][19][20] Recently, Waymouth et al developed (thio)urea anions for Brønsted acid-base synergistic catalytic ROP of cyclic esters. This catalytic system exhibits both high catalytic activity and good control.…”

Stereo-electronic contributions in yttrium-mediated stereoselective ring-opening polymerization of functionalracemicβ-lactones: ROP of 4-alkoxymethylene-β-propiolactones with bulky exocyclic chains

“…In a typical experiment, 13 in a glovebox, a Schlenk flask was charged with [Y(N(SiHMe 2 ) 2 ) 3 ](THF) 2 (8.8 mg, 14 μmol) and {ONNO t Bu 2 } ( 1d , 7.4 mg, 14 μmol), and toluene (0.25 mL) was next added. To this solution, iPrOH (107 μL of a 1% ( v / v ) solution in toluene, 1 equiv.…”

“…1 a – e The formation of isotactic polyesters from the ROP of racemic lactones is clearly much less common than that of their syndiotactic (heterotactic) counterparts; indeed, the latter syndio/hetero tacticities are often the result of a chain-end stereocontrol 1 a , b where the minimization of steric tilting in the transition state induces the regular, alternated enchainment of consecutive monomer units with the opposite configuration. On the other hand, the formation of isotactic polyesters from racemic cyclic esters usually requires the use of chiral catalysts, most often metal-based ones, 2 to proceed via a so-called enantiomorphic site control; isoselective ROP of racemic lactones with achiral catalysts is even less frequent and largely focused on rac -LA. 1,3 A recent, remarkable addition is the stereoselective ROP of eight-membered racemic cyclic diolides mediated by discrete rare earth-based catalysts developed by the group of Chen, which affords a variety of perfectly isotactic ( P m up to 0.99)‡‡ P m is the probability of meso linkages, that is, the enchainment of two monomer units with the same configuration.…”

Tetrabutylammonium Halides as Selectively Bifunctional Catalysts Enabling the Syntheses of Recyclable High Molecular Weight Salicylic Acid‐Based Copolyesters

“…[12] During the analyses of the 1 H NMR spectra of the polymerization mixtures (Table S1, entries 3-6, Figures S9-12), the obvious quartet peaks at 6.08 ppm and 5.74 ppm attracted our attention, which should be assigned to side products. In order to increase the amounts of side products, a potassium complex reported by our group [19] was applied to the ROP reaction, the related intensities of 6.08 ppm and 5.74 ppm signals increase obviously in the polymerization reaction mixture (Table S1 entry 23, Figure S8). After the separation via column chromatography, the side products are characterized to be cyclic dimers of SMG (DSMG) which also were confirmed by single crystal structures of rac-DSMG and meso-DSMG (Tables S6 and S7, Figure S2-6).…”