Effect of polymer topology on the curing process and mechanical characteristics of epoxy thermosets modified with linear or multiarm star poly(ε-caprolactone)

A well-defined multiarm star copolymer, hyperbranched poly(glycidol)-b-poly(ε-caprolactone), with an average of 100-110 arms per molecule and a molecular weight of arms of 1000 g/mol (s-PCL) and a linear PCL analog (l-PCL) were used as modifiers in the curing of diglycidylether of bisphenol A (DGEBA) using ytterbium triflate as cationic initiator. The effect of the polymer topology on the curing and gelation was studied by dynamic scanning calorimetry (DSC) and rheometry. The addition of s-PCL to the resin left the complex viscosity (η∗) practically unaltered. In contrast the addition of l-PCL incremented substantially the viscosity. The addition of star-shaped modifiers decreased the shrinkage after gelation in a higher extent than the linear analog. The homogeneity of pure DGEBA and modified thermosets was proved by dynamic thermomechanical analysis (DMTA) and electronic microscopy (SEM). The addition of star-like structures led to a higher impact energy fracture in comparison to pure DGEBA and l-PCL modified thermosets and to a lower effect on the microhardness than the linear analog.