Hyperbranched polyester as additives in filled and unfilled epoxy-novolac systems

The synthesis and characterization of a new type of hyperbranched polyester with a flexible ethoxylated Bisphenol-A structure and terminal hydroxyl groups is reported. The influence of the hyperbranched polyester on the curing and thermomechanical properties of both unfilled and silica filled epoxy-novolac systems was studied. The curing behavior was investigated by differential scanning calorimetry (DSC) and rheolometry. The addition of the hyperbranched polyester to the formulation reduced the contraction on curing of both unfilled and filled systems, while Tg of the cured samples dropped down with the increase of polyester content due to the flexible backbone structure of the modifier. SEM microscopy on the fractured surface of cured samples revealed a homogeneous morphology and a possible effect of polyester as a toughness enhancer.