New hyperbranched polyester modified DGEBA thermosets with improved chemical reworkability

The chemical reworkability of epoxy thermosets in alkaline solutions has been increased by adding a hyperbranched polyester (HBPE) as a reactive modifier to the diglycidyl ether of bisphenol A (DGEBA) cured by lanthanide triflates as cationic initiators. The presence of hydroxyl chain-ends in the HBPE allows the modifier to be linked covalently to the epoxy matrix through the monomer activated propagation mechanism, which occurs in cationic polymerizations. Yb(OTf)(3) leads to quicker curing than the lanthanum salt and to materials with the highest glass transition temperature (T-g). The addition of HBPE does not affect adversely the thermal stability and leads to a slight reduction of the global shrinkage. The T-g of the materials, the relaxed modulus and the linear thermal expansion coefficients are practically maintained by the addition of HBPE. (C) 2010 Elsevier Ltd. All rights reserved.