Highly Selective and Productive Synthesis of a Carbon Dioxide-Based Copolymer upon Zwitterionic Growth

Abstract

This work discloses a zwitterionic approach for selective copolymerization of carbon dioxide (CO 2 ) and propylene oxide (PO), producing poly(propylene carbonate) (PPC), a biodegradable polymer with broad applications. Small-molecule catalysts composed of triethylamine (TEA) and trialkyl boranes are effective for CO 2 / PO copolymerization with an alternating degree of >99% and a productivity of 171 g PPC/g catalyst. A diamine N,N,N′,N′-tetraethyl ethylenediamine (TEED) paired with trialkyl borane exhibited improved activity and productivity (up to 216 g PPC/g catalyst). By adjusting the Lewis acid−base pair, the PPC selectivity can be regulated to 99%. In addition, PPCs have medium regioregularity with a head-to-tail diad content of 80−82% and number-average molecular weights of up to 56.0 kg/mol with narrow polydispersity (below 1.2). The overall catalytic performance of these readily available simple molecules is better than that of previously reported organic catalysts for CO 2 /PO copolymerization. Successive insertion of PO and CO 2 into the Lewis pair leads to the formation of an end-to-end zwitterion featuring a TEB-masked anion and an onium cation, which is highly selective to the alternating copolymerization, as demonstrated by quantum mechanical calculations.

Heterocycle/Heteroallene Ring‐Opening Copolymerization: Selective Catalysis Delivering Alternating Copolymers

“…Feng and co-workers discovered that Et3B (Lewis acid) and PPNCl (Lewis base) combinations showed good activity for both CO2/PO (TOF 49 h -1 , 60 °C, 0.1 mol%, 10 bar, 83% PPC) and CO2/CHO ROCOP (TOF 600 h -1 , 80°C, 0.025 mol%, 10 bar, 99% PCHC). [39,41,42] DFT investigations support the rate determining step involving triethylborane epoxide and propagating chain-end coordination; this mechanism closely resembles earlier reports for metal/co-catalyst bimetallic pathways. Very recently, Wu and co-workers reported a quaternary ammonium tethered 9-borabicyclo(3.3.1)nonane, applied at 0.005 mol% loading, which shows high activity for CO2/CHO ROCOP (TOF 4900 h -1 , 150 °C, 15 bar).…”

“…Some of these organocatalysts may be attractive in terms of ease of use on a small scale and their lack of colour. Feng and co‐workers discovered that Et 3 B (Lewis acid) and PPNCl (Lewis base) combinations showed good activity for both CO 2 /PO (TOF 49 h −1 , 60 °C, 0.1 mol %, 10 bar, 83 % PPC) and CO 2 /CHO ROCOP (TOF 600 h −1 , 80 °C, 0.025 mol %, 10 bar, 99 % PCHC) [39, 41, 42] . DFT investigations support the rate‐determining step involving triethylborane epoxide and coordination of the propagating chain end (Figure 6); this mechanism closely resembles earlier reports for metal/co‐catalyst bimetallic pathways.…”

Heterocycle/Heteroallene Ring‐Opening Copolymerization: Selective Catalysis Delivering Alternating Copolymers

“…Feng and co-workers discovered that Et 3 B( Lewis acid) and PPNCl (Lewis base) combinations showed good activity for both CO 2 /PO (TOF 49 h À1 ,6 0 8 8C, 0.1 mol %, 10 bar, 83 % PPC) and CO 2 /CHO ROCOP (TOF 600 h À1 ,8 0 8 8C, 0.025 mol %, 10 bar,9 9% PCHC). [39,41,42] DFT investigations support the rate-determining step involving triethylborane epoxide and coordination of the propagating chain end (Figure 6);t his mechanism closely resembles earlier reports for metal/co-catalyst bimetallic pathways.V ery recently,W u and co-workers reported aquaternary ammonium-tethered 9borabicyclo(3.3.1)nonane,a pplied at 0.005 mol %l oading, which shows high activity for CO 2 /CHO ROCOP (TOF 4900 h À1 ,1 50 8 8C, 15 bar). [40] Ar elated ammonium salt quadruply tethered to borane moieties achieves CO 2 /epichlorhydrin (ECH) ROCOP to produce awhite polymer (TOF 7h À1 , 25 8 8C, 0.1 mol %, 25 bar,9 9% polymer;F igure 7).…”

Synthesis of Diverse Polycarbonates by Organocatalytic Copolymerization of CO2 and Epoxides: From High Pressure and Temperature to Ambient Conditions

“…Recently, the same group reported pinwheel‐shaped tetranuclear organoboron catalysts for the challenging copolymerization of CO 2 with epichlorohydrin [47] . Zhang and co‐workers reported copolymerization of CO 2 with PO by simple and commercial tertiary amine/TEB Lewis pairs, which displayed high activity and selectivity via a zwitterionic copolymerization mechanism [48] . However, the synthesis of CO 2 ‐PCs by organocatalysts is still in its infancy, and the development of diverse organocatalysts with high activity and selectivity is a great challenge.…”