Poly(carbonate acetal) vitrimers with enhanced thermal properties and closed-loop thermal recyclability derived from waste polycarbonate-derived polyaldehyde and pentaerythritol/erythritol/D-sorbitol

We synthesized three poly(carbonate acetal) vitrimers (PCA-P, PCA-E, PCA-S) by condensing a waste polycarbonate-derived polyaldehyde (WPC-CHO) with pentaerythritol, erythritol, and D-sorbitol, using 0.5–4.0 mol% p-toluene sulfonic acid (pTSA) as a catalyst. Flexible PCA films emerged at pTSA concentrations ≥1 mol%, indicating a critical threshold of acid for effective condensation. The glass transition temperatures (T_g) of the films remained consistent across pTSA concentrations but varied based on the multi-alcohol structure, with T_g values of 178 °C for both PCA-P and PCA-S, and 142 °C for PCA-E, suggesting superior performance of pentaerythritol and D-sorbitol over erythritol as building blocks. Among these, the PCA-S series exhibited the best performance and utilized the least expensive starting materials, achieving the highest cost-performance index. The PCAs, featuring covalent adaptable polyacetal networks, facilitated thermal reprocessing through acetal metathesis. The second reprocessed PCA-P and PCA-S maintained similar thermal and mechanical properties to their original forms, demonstrating a closed-loop recycling. These polymers showed stability in THF/H₂O (4/1) with 0.1–1.0 M H₂SO₄ at 25 °C, but can be degraded at 50 °C within 5 hours in both 0.5 M H₂SO₄ and HCl THF/H₂O (4/1) solutions. NMR analysis of the degraded PCA-P confirmed the recovery of WPC-CHO and pentaerythritol. Furthermore, PCA-based carbon-fiber-reinforced plastics (CFRPs) were prepared, and the carbon fibers were successfully recovered after acid degradation without any loss to their structural or tensile integrity.