Recyclable and Degradable Ionic-Substituted Long-Chain Polyesters

Abstract

Ionic groups can endow apolar polymers like polyethylene with desirable traits like adhesion with polar compounds. While ethylene copolymers provide a wide range of tunability via the carboxylate content and neutralization with different cations, they lack degradability or suitability for chemical recycling due to their all-carbon backbones. Here, we report ioncontaining long-chain polyesters with low amounts of ionic groups (M n = 50−60 kg/mol, <0.5 mol % of ionic monomers) which can be synthesized from plant oils and exhibit HDPE-like character in their structural and mechanical properties. In the sulfonic acid as well as neutralized sulfonate-containing polyesters, the nature of the cation counterions (Mg 2+ , Ca 2+ , and Zn 2+ ) significantly impacts the mechanical properties and melt rheology. Acid-containing polyesters exhibit a relatively high capability to absorb water and are susceptible to abiotic degradation. Enhanced surface wettability is reflected by facilitation of printing on films of these polymers. Depolymerization by methanolysis to afford the neat long-chain monomers demonstrates the suitability for chemical recycling. The surface properties of the neutralized sulfonate-containing polyesters are enhanced, showing a higher adsorption capability. Our findings allow for tuning the properties of recyclable polyethylene-like polymers and widen the scope of these promising materials.

Synthesis and Deconstruction of Polyethylene-type Materials

“…The depolymerization and repolymerization of PE-type polyesters was found to be robust, as functional groups such as ionic groups and thioether groups or furan-containing monomers did not interfere with the depolymerization process. Even mixtures of diacids could be recovered upon depolymerization in the same ratio as used in the initial polycondensation .…”

“…The in-chain ester groups slightly increase the surface free energy of the material, enabling the adhesion of hydrophilic ink after printing on PE-18,18 films compared to HDPE films. This effect can be enhanced by the introduction of small amounts of ionic groups …”

“…The isolation of these monomers after solvolysis can be achieved by selective crystallization of the long-chain diacid, and it is further aided by the volatility of the ethylene glycol component. 167 The depolymerization and repolymerization of PE-type polyesters was found to be robust, as functional groups such as ionic groups 179 and thioether groups 194 or furan-containing monomers 195 did not interfere with the depolymerization process. Even mixtures of diacids could be recovered upon depolymerization in the same ratio as used in the initial polycondensation.…”

Closed-Loop Recyclable and Nonpersistent Polyethylene-like Polyesters

“…This leads to embrittlement and fragmentation of the specimens, which increases the surface area and, in combination with the observed molar mass reduction, is anticipated to accelerate and promote further degradation. As an alternative to this blending approach, acid functionalities can be incorporated into the polymer chain . Long-chain polyesters containing small amounts of sulfonic acid groups exhibit enhanced water uptake, which facilitates the acid-catalyzed cleavage of the in-chain ester groups.…”

“…As an alternative to this blending approach, acid functionalities can be incorporated into the polymer chain. 58 Long-chain polyesters containing small amounts of sulfonic acid groups exhibit enhanced water uptake, which facilitates the acid-catalyzed cleavage of the in-chain ester groups. Note that ionic in-chain groups not only enable hydrolytic degradability but also benefit the surface properties of HDPE-like polymers allowing for printability on films.…”