Miscibility and crystallization of thermosetting polymer blends of unsaturated polyester resin and poly(∈-caprolactone)

Poly(∈-caprolactone) (PCL) was found to be miscible with uncured polyester resin, i.e. oligoester (OER), as shown by the existence of a single glass transition temperature (T g ) in each blend. However, PCL was judged to be partially miscible with crosslinked polyester resin (PER) which was concluded from the results of thermal analysis. Fourier-transform infrared (FT-i.r.) studies revealed that intermolecular hydrogen bonding interaction between the components is an important driving force to the miscibility of PCL/OER blends and the partial miscibility of crosslinked PCL/PER blends. The importance of entropy contribution to the miscibility of thermosetting polymer blends is also shown from the FT-i.r. results. The spherulitic morphology of the blends was remarkably affected by crosslinking. The birefringent spherulites were observed in the uncured PCL/OER blends, whereas a distinct pattern of extinction rings, which was absent either in the pure PCL or in the uncured PCL/OER blends, was apparent in the crosslinked PCL/PER blends.