New chemically reworkable epoxy coatings obtained by the addition of polyesters with star topologies to diglycidyl ether of bisphenol A resins

Abstract

A new multiarm star with hyperbranched aromatic–aliphatic polyester core and poly(ɛ-caprolactone) arms (HBPCL) was synthesized and characterized. Mixtures of diglycidyl ether of bisphenol A (DGEBA) resin and different proportions of this star type modifier were cured using a thermal cationic curing agent, Yb(OTf)3. The HBPCL prepared has hydroxyl groups as chain ends, which are capable of chemically incorporating to the epoxy matrix by means of the monomer activated mechanism. This, together with the chemical structure of the modifier, allowed the preparation of new homogeneous thermosets for coating applications. The curing mixtures were investigated by differential scanning calorimetry (DSC) to study the curing process and evaluate the kinetic parameters of the formulations. These studies demonstrated that HBPCL decreased the curing rate and affected the gelation process. The thermosets obtained showed an improvement in impact strength with a discrete reduction of the Tg. The modified coatings showed an increased reworkability in alkaline solution with the maintenance of thermal stability.