Switchable Catalysis Improves the Properties of CO₂-Derived Polymers: Poly(cyclohexene carbonate-b-ε-decalactone-b-cyclohexene carbonate) Adhesives, Elastomers, and Toughened Plastics

Abstract

Carbon dioxide/epoxide copolymerization is an efficient way to add value to waste CO2 and to reduce pollution in polymer manufacturing. Using this process to make low molar mass polycarbonate polyols is a commercially relevant route to new thermosets and polyurethanes. In contrast, high molar mass polycarbonates, produced from CO2, generally under-deliver in terms of properties, and one of the most widely investigated, poly­(cyclohexene carbonate), is limited by its low elongation at break and high brittleness. Here, a new catalytic polymerization process is reported that selectively and efficiently yields degradable ABA-block polymers, incorporating 6–23 wt % CO2. The polymers are synthesized using a new, highly active organometallic heterodinuclear Zn­(II)/Mg­(II) catalyst applied in a one-pot procedure together with biobased ε-decalactone, cyclohexene oxide, and carbon dioxide to make a series of poly­(cyclohexene carbonate-b-decalactone-b-cyclohexene carbonate) [PCHC-PDL-PCHC]. The process is highly selective (CO2 selectivity >99% of theoretical value), allows for high monomer conversions (>90%), and yields polymers with predictable compositions, molar mass (from 38–71 kg mol–1), and forms dihydroxyl telechelic chains. These new materials improve upon the properties of poly­(cyclohexene carbonate) and, specifically, they show good thermal stability (T d,5 ∼ 280 °C), high toughness (112 MJ m–3), and very high elongation at break (>900%). Materials properties are improved by precisely controlling both the quantity and location of carbon dioxide in the polymer chain. Preliminary studies show that polymers are stable in aqueous environments at room temperature over months, but they are rapidly degraded upon gentle heating in an acidic environment (60 °C, toluene, p-toluene sulfonic acid). The process is likely generally applicable to many other lactones, lactides, anhydrides, epoxides, and heterocumulenes and sets the scene for a host of new applications for CO2-derived polymers.

Visible-Light-Curable Solvent-Free Acrylic Pressure-Sensitive Adhesives via Photoredox-Mediated Radical Polymerization

“…The peel strength (2.8–8.0 N cm −1 ) and loop tack (4.1–8.2 N cm −1 ) of the prepared PSAs indicated that the PSAs could be used as general acrylic PSAs and optically clear adhesives [ 8 , 47 , 48 , 49 ]. In particular, the PSA obtained using a DBM concentration of 0.1 mol% and a 4DP-IPN loading of 10 ppm presented both excellent creep resistance (holding time > 100 h) and transparency (98.5%), which rendered it the most suitable PSA as an optically clear adhesive for electronics.…”

Controlled Ring-Opening Polymerization of O-Carboxyanhydrides to Synthesize Functionalized Poly(α-Hydroxy Acids)

“…Additional efforts should be also directed to close the urgent gap in creating highly stereoselective and sequence-controllable ROP that allows for immediate access to functionalized PAHAs, as similar remarkable controls have been achieved in the ROP of lactones and other heterocyclic monomers. [108][109][110][111][112] One of the foreseeable challenges is the scale-up of monomer synthesis. Unlike monomers of LA and many anhydrides that have seen success under large-scale industrial production, 113 most of OCA monomers are subjected to repetitive recrystallization for potential industrial scale-up.…”

Photocatalyst-Independent Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides: Stereocontrol and Mechanism

“…The wide range of T g values also potentially allows for the preparation of multiblock thermoplastic elastomers. [97][98][99]…”