Ring-Opening Copolymerization Using a Chromium Complex with a Readily Available Aminotriphenolate Ligand

Abstract

A new chromium(III) complex (2) with a readily available aminotriphenolate ligand (L tBu,tBu ) was developed as an efficient catalyst for alternating ring-opening copolymerization of cyclic epoxides and anhydrides to afford polyesters. The single-crystal structure of 2 exhibits an octahedral geometry despite the high steric profile of L tBu,tBu . After the reaction conditions were optimized, complex 2 in the presence of a cocatalyst produced perfectly alternating polyesters with high molecular weights (up to M n = 44.2 kg/mol) and low dispersity at high conversion. In addition, various polyesters prepared using combinations of comonomers exhibited relatively high glass transition temperatures.

Structural Metamorphoses of d-Xylose Oxetane- and Carbonyl Sulfide-Based Polymers In Situ during Ring-Opening Copolymerizations

“…This observation was further confirmed by their 1 H NMR spectra, where polymers 11 and 12 displayed signals at 2.89−2.60 ppm, corresponding to the methylene protons of the thioether linkages, yet had an absence of methylene protons resonating at 3.17−3.07 ppm, characteristic of the methylene protons adjacent to monothiocarbonates (Figures S11 and S12). Further, the 13 C NMR spectra of 11 and 12 displayed a single peak at 153.2 ppm, suggesting regioregularity along the polymer backbone. Copolymers 7− 10, which were synthesized at 60 °C ≤ T < 120 °C, contained combinations of monothiocarbonate, carbonate, and thioether linkages, as demonstrated by their 1 H NMR, 13 C NMR (Figure S19), and FT-IR (Figure S22) spectra.…”

“…1 H- 13 C heteronuclear multiple-bond (HMBC) 2D NMR analyses were employed to examine the structural details and the connectivity of poly(MTC), poly[(MTC)-co-(CTE)], and poly(CTE) to investigate our proposed mechanism. The HMBC spectrum of poly(MTC) displayed two cross peaks at (169.5, 5.29 ppm) and (169.5, 3.12 ppm) resulting from 3 J CH couplings between each methine proton (H c ) and the methylene proton (H e ) with the monothiocarbonate carbonyl carbon, respectively, indicating that the monothiocarbonate monomeric repeating units were connected regioregularly via head-to-tail linkages (Figure 2A).…”

“…The quest for degradable, sustainable polymers from renewable resources is becoming an increased priority, along with and in efforts to address coincident events of plastic pollution, climate change, and the energy transition away from petroleum-based feedstocks. There has been an emphasis on developing chemical transformations involving molecular or macromolecular materials of natural origin to afford functional polymers, thereby advancing efforts toward achieving sustainability for the growing plastic demand. − Relevant to this aim, copolymerizations of small molecule natural products with carbon dioxide or other complementary feedstocks, some of which originate as waste from fossil fuel or human-made supplies, are of particular interest for the production of a broad range of types of sustainable polymeric materials. ,− For instance, the general class of ring-opening copolymerizations (ROCOPs) ,− ,− of cyclic ethers with comonomers, such as carbon dioxide (CO 2 ), ,− carbonyl sulfide (COS), , carbon disulfide (CS 2 ), , aryl isocyanates, , and cyclic anhydrides, ,,,,− has provided access to diverse backbone compositions, including polycarbonates, poly­(monothiocarbonate)­s, poly­(thiocarbonate)­s, polyurethanes or polyallophanates, and polyesters, respectively. However, a common limitation to this copolymerization strategy is the use of cyclic ethers from non-renewable sources, which adversely affects overall sustainability.…”

“…The absence of ether 1 H NMR signals confirmed that the degrees of xylose oxetane and COS alternation were >99%. 13 C NMR spectroscopy of 1 indicated that no O/S ER occurred as there was a single resonance observed at 169.9 ppm, the characteristic resonance frequency for a monothiocarbonate linkage (Figure S1). Although poly(MTC) was afforded at 40 °C, its molar mass was relatively low.…”

“…The degree of xylose oxetane and COS alternation remained at >99% with a lack of ether formation; however, O/S ERs occurred, resulting in poly-[(MTC)-co-(CTE)] having combinations of monothiocarbonate, carbonate, and thioether linkages along the polymer backbone. The formation of monothiocarbonate and carbonate functionalities was determined by the presence of two signals in the 13 C NMR spectra resonating at 169.9 and 153.5 ppm, respectively (Figures S2−S6). To our surprise, dithiocarbonates, another possible linkage during O/S ERs, were not observed, as confirmed by the absence of a characteristic resonance signal at ca.…”