Multicomponent Polymerization of β-Propiolactone, Epoxides, Anhydrides, and CO₂: Synthesizing Sustainable Materials with Widely Adjustable Properties

Multicomponent polymerization of three or more monomers can potentially introduce different subunits into a polymer chain with adjustable composition and sequence distribution to improve the material properties and leverage their respective advantages. This study presents multicomponent polymerization reactions of a mixed-monomer feedstock of epoxides, β-propiolactone (BPL), anhydrides, and CO2 under mild conditions. The binary catalyst system consisting of (salcy)Co(III)OTs (salcy = N,N′-bis(3-tert-5-fluoro-butylsalicylidene)-1,2-diaminocyclohexane; OTs = p-toluenesulfonate) and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) is capable of catalyzing the ring-opening polymerization of BPL, and the alternating copolymerization of epoxides and anhydrides or CO2. Additionally, the versatile catalyst is very efficient in the terpolymerization of epoxides, BPL, and anhydrides, or CO2. The cleavage of the alkyl C–O bond rather than the acyl C(═O)–O bond of BPL, through the nucleophilic attack of carboxylate or carbonate during polymerization, significantly prevents transesterification side reactions, thereby resulting in the terpolymerization proceeding in a controlled manner. The gradient or statistical distributions of two types of subunits could be observed in the resultant terpolymers. Notably, (salcy)Co(III)OTs/MTBD-mediated multicomponent polymerization of epoxides, BPL, phthalic anhydride (PA), and CO2 afforded a novel diblock polymer constituting epoxide/PA/BPL and epoxide/CO2/BPL terpolymer segments, while the quaternary polymerization involving the less reactive glutaric anhydride (GA) generated a random epoxide/GA/CO2/BPL polymer. The controlled and random polymerization pathway offers a promising synthesis route to sustainable materials with a mixed-glass transition temperature that can be adjusted over a wide range.