Micro-heterogeneity of urethane vinylester resin networks

The morphological structure of a fully cross-linked vinylester Atlac 580 re sin has been studied by using modulated differential scanning calorimetry ( MDSC). The results show that the networks exhibit a diphasic structure, cha racterised by the presence of two glass transition temperatures (T-g) It is believed that the two phases are composed of a polystyrene-rich phase and a vinylester-rich phase, which results from phase segregation during radica l copolymerisation. An annealing process below the glass transition tempera tures can make the separated phases readily visible. Furthermore, the resul ts demonstrate that MDSC can offer better resolution and sensitivity than c onventional DSC and dynamic mechanical thermal analysis. This enables overl apping glass transitions (with T(g)s closer than 10 degrees C) to be distin guished successfully. (C) 2000 Elsevier Science Ltd. All rights reserved.