Short-Loop Chemical Recycling via Telechelic Polymers for Biobased Polyesters with Spiroacetal Units

Abstract

Spirocyclic acetal structures have recently received growing attention in polymer science due to their dual potential to raise the glass transition temperature (T g ) and enable chemical recycling of biobased polymers. In the present work, a vanillinbased diol with a spirocyclic acetal structure was incorporated in a series of rigid amorphous polyesters based on neopentyl glycol and dimethyl terephthalate (DMT). Up to 50 mol % of spirocyclic diol (with respect to DMT) could be incorporated in the copolyesters, but a reasonably high molecular weight was only achieved when ≤30 mol % of the spirocyclic diol was used. The presence of the spiroacetal units in the polyesters not only enhanced the T g (up to 103 °C) and thermal stability (T 5 ≥ 300 °C) but also the oxygen barrier of solution-cast films. We found that the acetal units in the copolyesters could be selectively hydrolyzed under acidic conditions while virtually retaining all of the ester bonds in the polymer backbone. After acidic hydrolysis, telechelic polymers exclusively terminated by two aldehyde end groups were obtained. In this work, we have demonstrated that these telechelic polyesters can be conveniently converted back into poly(acetal-ester)s via cycloacetalization reactions with pentaerythritol.

Improved chemical recyclability of 2,5-furandicarboxylate polyesters enabled by acid-sensitive spirocyclic ketal units

“…It should be noted that the estimation of the preliminary E factor was purely based on the waste-to-product ratio and was only to obtain a rough assessment of the environmental impact of the process. 8,13 It did not include any contributions from the solvent or catalyst. Therefore, a meaningful conclusion can only be derived once a full-scale process optimization has been performed.…”

“…Lately, chemical recycling has emerged as an attractive alternative, in which polymer wastes are depolymerized to obtain the starting monomers/building blocks or oligomers, which are then repolymerized to obtain virgin or new polymeric materials with a similar quality as the original. 6–11 This circular use of plastics offers not only a feasible solution to the end-of-use issue of materials, but also provides a closed-loop approach towards the circular economy. 12 As a result, there have been huge demands for newly designed biobased polymers to enable and facilitate their chemical recycling.…”

“…For example, the acetal bonds in poly(acetal-ester)s have been selectively hydrolyzed under acidic conditions to yield aldehyde end-capped telechelic polyesters, which were repolymerized to poly(acetal-ester)s via cycloacetalization with pentaerythritol. 8 Since the process requires only fewer bonds to be broken and reformed, it was presented as short-loop recycling and energy efficient as large fraction of initial bond-forming energy was retained.…”

From vanillin to biobased aromatic polymers

“…The glass transition temperature of the obtained polyester (PNVT) was up to 103 °C. The degradation under acidic conditions yielded telechelic polymers consisting entirely of aldehyde groups as end groups, which were confirmed by MALDI-TOF-MS. 124…”

Ultra-Tough Vanillin-Based Polyester Hot-Melt Adhesive through Multiple Oxygenated Groups

“…Adhesives serve a crucial part in human life and are extensively utilized in the industrial bonding, packaging, building manufacturing, electronic device, and aerospace industries. − However, at present, adhesives still face challenges such as poor bond strength (such as epoxy resins), − toxicity, irreversible curing (such as acrylics, polyurethanes, and organic silicones), , and limited conditions of use (such as anaerobic adhesives, UV adhesives, and solvent-based adhesives). − Polyester hot-melt adhesives are a typical example of solvent-free, ecologically friendly adhesives that meet the demands of the adhesive industry for energy efficiency, nontoxicity, low cost, reusability, and excellent performance. , Linear saturated polyesters are generally utilized as hot-melt adhesives, prepared by transesterification, esterification, and polycondensation reactions, which is simple and easy to process. − However, these raw materials used in commercial hot-melt adhesives are usually derived from petroleum resources and do not meet the requirements of sustainable development. − Yet, compared to petrochemical products, which come in a large variety, the number of biobased monomers that can be employed to create biomass polyester hot-melt adhesives is substantially fewer. − For example, Zheng et al used biobased 1,5-pentanediol as a replacement for petroleum-derived 1,6-hexanediol for polyester hot-melt adhesives . Kim et al prepared a polyester hot-melt adhesive using polybutylene terephthalate modified with dimer acid methyl ester derived from fatty acid methyl esters .…”