The ability of highly cross-linked thermoset materials to relax stresses by network chainsegment mobility above or just below Tg is generally limited. We describe materials in whichsome of the cross-links have been replaced by dimers of quadruple hydrogen bonding ureidopyrimidinone(UPy) moieties, which act as reversible cross-links. Materials based on mixturesof ??-caprolactone and L-lactic acid, and containing different ratios of covalent and UPy dimercross-links, were synthesized and their thermal and mechanical properties were tested byDifferential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA). Thepresence of reversible cross-links results in superior relaxation of stresses even below Tg, aswitnessed by the creep and stress relaxation behavior. These properties bode well for potentialapplications, e.g. in coatings technology.