Graft interpenetrating polymeric networks of epoxy resin and polydimet
hylsiloxane (PDMS) were synthesized using 3-aminopropyltrimethoxysilan
e (gamma-APS) as coupling agent. The dynamic mechanical analysis shows
partially mutual compatibility between these two thermodynamically im
miscible polymers. Due to the inappropriate domain size and the poor c
ohesive properties between epoxy resin and PDMS domain, the fracture e
nergy (G(IC)) decreased drastically at low PDMS content (5%). While th
e PDMS domain size increased according to the PDMS contents, the fract
ure energy was then improved. This experimental result indicates that
PDMS with an appropriate domain size can be used as a toughness modifi
er for polyfunctional epoxy resins. (C) 1997 Elsevier Science Ltd.