Paper published in the Journal of High Performance Polymers (1996) 8 67-82.
S F Bush with J M Methven and D R Blackburn
Abstract
This paper describes a new class of thermosetting polymer blends. The blends are now used commercially in the manufacture of sheet moulding compounds (SMC) where they exhibit important advantages compared with conventional systems. The new compositions comprise a cross-linkable base resin and unsaturated monomer in which the base resin is dissolved and a saturated additive resin which has a crystalline melting temperature Tm below the temperature Tr at which cross-linking occurs. Between Tr and Tm the additive and base resin form a single liquid phase, which on cooling thickens reversibly to a leathery sheet with no bulk phase separation. The paper describes the mechanisms underlying this viscosity switch phenomenon and the partial compatibility criterion used to select the resin-additive combinations which exhibit this behaviour.