Dynamic Bonds Enable Repair and Reprocessing of Glycol-Modified PET

Abstract

Self-healing polymers promise extended lifetimes, improved sustainability, and reduced maintenance costs. These attributes are particularly valuable in protective coatings. Here, we introduce a new class of healable glycol-modified polyethylene terephthalates (PETGs) that leverage hindered urea bonds (HUBs) to enable rapid, intrinsic repair through dissociative exchange. These polymers are synthesized in a readily manner from hydroxy-terminated PETG telechelics, hexamethylene diisocyanate, and N,N’-di-tert-butylethylenediamine (TBEU), which introduces the sterically demanding amines required for HUB formation. The systematic variation in TBEU content reveals a tradeoff between mechanical robustness and healing efficiency. Higher TBEU levels improve the healability but reduce strength. Formulations with nearly equimolar fractions of TBEU and PETG telechelic offer an attractive balance, combining a tensile strength of 20 MPa with complete crack disappearance in just 30 s at 130°C. However, healing causes a reduction in molecular weight and embrittlement, likely due to trapping of dissociated isocyanates and amines upon cooling to the glassy state. A comparative analysis with dynamic PETGs incorporating other dynamic bonds is provided to contextualize the performance of the new polymers.