Initiator-Free In Situ Photocuration for Constructing Degradable and Closed-Loop Recyclable Poly(disulfide)s from Renewable Biomass

Abstract

The development of sustainable polymers that combine high performance, reprocessability, and closed-loop recyclability remains a fundamental challenge. Herein, two imine-containing thioctic acid esters with different functionalities (bifunctional TF-HMDA and trifunctional TF-TAEA) were synthesized from renewable thioctic acid (TA) and 5-hydroxymethylfurfural (HMF) via esterification and aldehyde-amine condensation. Both monomers undergo rapid ring-opening photopolymerization under initiator-free and solvent-free conditions, forming cross-linked poly(disulfide) films with imine-based cross-linking points. The films can be directly photocured without any photoinitiators or additional catalysts. The resulting polymer films exhibit good thermal and mechanical properties, with 5% weight-loss temperatures ranging from 217 to 235 °C and tensile strengths from 57 to 78 MPa. Furthermore, owing to the integration of dual-dynamic disulfide and imine bonds, the poly(disulfide) networks are capable of self-healing under mild conditions without external additives. Remarkably, the polymer also demonstrates closed-loop recyclability. The original monomers can be recovered in high purity and repolymerized without significant loss of thermal or mechanical performance. By combining renewability, catalyst-free polymerization, dual-dynamic chemistry, and end-of-life circularity, this work establishes a versatile platform for next-generation sustainable polymers that addresses both feedstock sustainability and the challenge of plastic waste.