Ring-opening copolymerization (ROCOP) of epoxide/anhydride/CO2 for the synthesis of CO2-based copolymers is a promising process, because CO2 is an abundant, nontoxic, and low-cost monomer and has been considered as one of the most attractive renewable C1-resources. Although considerable progress has been made in the past decade, synthesis of block copolymers from mixed monomers through a one-pot polymerization is still a great challenge. Selective terpolymerizations of epoxide/anhydride/CO2 have been exclusively catalyzed by metal-based catalysts. There has been no success in using organocatalysts that can bridge ROCOP of epoxide/CO2 and ROCOP of epoxide/anhydride to produce CO2-based block copolymers, although a few organocatalysts have been independently used for either ROCOP. In this contribution, the PPNCl/TEB Lewis pair was selected as the organocatalyst to conjoin these two processes for one-pot ROCOP of epoxide/anhydride/CO2. NMR investigations of cyclohexene oxide (CHO)/phthalic anhydride (PA)/CO2 copolymerization revealed that polyester production was much faster than polycarbonate production and that polycarbonate was not formed until PA monomer was almost fully consumed (≥95% of conversion). Therefore, diblock copolymers composed of poly­(PA-alt-CHO) and PCHC blocks with very little tapering were synthesized in this one-pot and one-step route under metal-free conditions. The pre-rate-determining mechanism has been proposed for this chemoselectivity, which was further verified by DFT calculations. Subsequently, poly­(PA-alt-CHO)-b-PCHC diblock copolymers without any tapering were successfully synthesized by sequential ROCOP of CHO/PA and ROCOP of CHO/CO2. NMR and GPC analysis of the resultant polymers demonstrated the formation of well-defined poly­(PA-alt-CHO)-b-PCHC diblock copolymers with unimodal and narrow molecular weight distribution.

Organophosphazenes combined with triethylborane (TEB) were selected as binary organocatalyts for the copolymerization of CO2 and epoxides. Both the activity and selectivity were highly dependent on the nature of phosphazenes. 2,4,6‐Tris[tri(1‐pyrrolidinyl)‐iminophosphorane]‐1,3,5‐triazine (C3N3‐Py‐P3) with a relatively low basicity (pKa=26.5 in CD3CN) and a bulky molecular size (φ=1.3 nm) exhibited an unprecedented efficiency (TON up to 12240) and selectivity (>99 % polymer selectivity and >99 % carbonate linkages) toward copolymerization of CO2 and cyclohexene oxide (CHO), and produced CO2‐based polycarbonates (CO2‐PCs) with high molar masses (Mn up to 275.5 kDa) at 1 MPa of CO2 and 80 °C. Surprisingly, this binary catalytic system achieved efficient CO2/CHO copolymerization with TOF up to 95 h−1 at 1 atm pressure and room temperature.

Phosphazenes as organocatalysts for the synthesis of polymers have evolved to powerful tools, and their catalytic performances highly depend on the basicity and molecular structure (size and shape). Therefore, designing phosphazenes with tunable basicity and molecular structure is greatly promising for the development of organocatalysts with improved catalytic properties, for example, high activity and selectivity. In this contribution, 2,4,6-tris[tri(dimethylamino)iminophosphorane]-1,3,5-triazine (C 3 N 3 -Me-P 3 ) and 2,4,6-tris[tri(1-pyrrolidinyl)iminophosphorane]-1,3,5-triazine (C 3 N 3 -Py-P 3 ) containing a 1,3,5-triazine-core were designed and synthesized. NMR spectroscopy analysis and single-crystal X-ray diffractions reveal that C 3 N 3 -Me-P 3 and C 3 N 3 -Py-P 3 , particularly the latter, show relatively low basicity, similar as t-BuP 1 , but have a bulky molecular size, similar as t-BuP 4 . C 3 N 3 -Me-P 3 and C 3 N 3 -Py-P 3 were successfully employed as organocatalysts for the ring-opening alternating copolymerization (ROAC) of anhydrides and epoxides with high activity. The produced polyesters were characterized using NMR spectroscopy, GPC and MALDI TOF, revealing perfectly alternating sequence, controlled molar mass and low dispersity and suggesting highly controlled ROAC reactions. Thus, well-defined triblock polyester P(PA-alt-CHO)-b-P(PA-alt-PO)-b-P(PA-alt-CHO) was facilely synthesized by one-pot reaction via sequential addition of two different epoxides.

The synthesis of high‐molecular‐weight polyesters via the ring‐opening alternating copolymerization (ROAC) of cyclic anhydrides and epoxides using organocatalysts remains a major challenge. In this context, the organic cyclic trimeric phosphazene base (CTPB) was used as an efficient catalyst for the ROAC of phthalic anhydride (PA) with epoxides. It was found that the activity and PA conversion dramatically increased with the addition of triethyl borane (TEB) as a cocatalyst, even a small amount of TEB, for example, 5 mol % relative to CTPB. The molecular structures of obtained polyesters were characterized by nuclear magnetic resonance (1H NMR, 13C NMR) and matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI TOF), which demonstrated the formation of perfectly alternating polyesters with unimodal and narrow molecular weight distributions. Different molecular weight polyesters (up to 118.5 kg mol−1) were facilely prepared by reducing the loading of CTPB and TEB, while the polymerizations were fast (turnover frequency, TOF up to 500 h−1). Thermal analysis of the resulting polymers indicated that the alternating polyesters were amorphous, and their Tgs increased with the increment of molecular weights. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020, 58, 803–810

The synergetic binary phosphazene/triethylborane (TEB) system is highly active and selective towards the ring‐opening alternating copolymerization of CO2 with different epoxides to prepare diverse CO2‐based polycarbonates (CO2‐PCs). In their Research Article (e202111197), Shaofeng Liu, Zhibo Li, and co‐workers report that this metal‐free organocatalyst can efficiently copolymerize CO2 with cyclohexene oxide under ambient conditions (1 atm pressure and room temperature), which is an environmentally friendly and more carbon‐balanced way toward CO2 utilization.