Alkali Metal Carboxylates: Simple and Versatile Initiators for Ring-Opening Alternating Copolymerization of Cyclic Anhydrides/Epoxides

Abstract

In this contribution, we thoroughly investigated the ring-opening alternating copolymerization (ROAC) of cyclic anhydride and epoxide by using commercially available alkali metal carboxylates (AMCs) as the simple and green initiators. The idea of our work is based on the coordination effects of epoxide on an AMC and the formation of AMC–epoxide adducts, which will weaken the interaction between metal cation and its carboxylate counterion and therefore render the carboxylate to feasibly attack epoxides in a nucleophilic manner at high temperature. The coordination effects of epoxide on the AMC could be proved by Fourier transform infrared (FT-IR) spectroscopy and density functional theory (DFT) calculations. AMCs could effectively catalyze the copolymerization of phthalate anhydride (PA) and cyclohexene oxide (CHO) in bulk at 110 °C, affording polyesters with perfectly alternating structure. Potassium acetate (KOAc) was able to copolymerize some common cyclic anhydrides and epoxide, allowing for the preparation of polyesters with structural diversity. Of note, KOAc could mediate ROAC of PA with propylene oxide (PO) with a high molar feed ratio of [KOAc]/[PA]/[PO] = 1:20 000:150 000, affording poly­(PA-alt-PO) with high molecular weight (>100 kDa). Finally, two different polymerization mechanisms, including anionic polymerization and cooperative catalysis, have been proposed according to the interaction strength between metal cation and carboxylate anion. In the “cooperative catalysis” mechanism, the alkali metal cation served as the Lewis acid to activate epoxide and cyclic active species were generated.

From Impossible to Possible: Atom‐Economic Polymerization of Low Strain Five‐Membered Carbonates

“…Terminal hydroxyl group analysis indicated two ring-opening route of PO with a priority to methine carbon (Figure S49). In contrast to previous works involving the formation of polyether linkages from epoxides homopolymerization [63,65,[67][68][69] or other side reactions via isomerization of PO, [70] the ROAC of PC/PA ensured a completely alternating polyester structure owing to the slowrelease of PO despite under such a high temperature as 200 °C (Figure S50). Also, the collected gas was confirmed as CO 2 with a purity of 99.9 % by GC-MS measurement (Figure 3d), suggesting a well-defined decarboxylation reaction of PC.…”

“…On the basis of the above-mentioned mechanism of in situ release of PO, we proposed a strategy of ROAC of PC/ cyclic anhydrides to realize efficient utilization of PC. Owing to its high activity with epoxides in polyester synthesis, PA [63][64][65][66] was selected to demonstrate the feasibility of our strategy. The preliminary results of copolymerization of PC/ PA were summarized in Table 1.…”

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

“…Angewandte Chemie International Edition Figure 12: Selection of high performance CHO/PA ROCOP catalysts. [57,58,[72][73][74][75] Most catalysts active for CO2/epoxide are also active for anhydride/epoxide ROCOP, yet the reverse isn't necessarily true. For example, Lewis base catalysts only form c5c for CO2/epoxides, but catalyse anhydride/epoxide ROCOP at appropriate temperatures.…”

Construction of triblock copolyesters via one-step switchable terpolymerization of epoxides, phthalic anhydride and ε-caprolactone using dual urea/organic base catalysts

“…Moreover, it was found that the ROAC cycle of PO/PA was faster than the ROP cycle of LA using TEB/DBU, unlike those previously reported. 33 Very recently, based on the ROAC of epoxides and anhydrides catalyzed by alkali metal carboxylates, 34 Satoh et al (2021) successfully employed these environmentally benign catalysts for the switchable ROAC and ROP of various combinations of epoxides, anhydrides, cyclic esters and initiators to achieve sequence-controlled multiblock polyesters with high effectiveness and selectivity. 17…”