EFFECT OF CURE SHRINKAGE ON THE MISCIBILITY OF A RUBBER WITH A THERMOSETTING POLYMER

A theoretical simulation of the effect of cure shrinkage on the miscib ility of a polydisperse rubber with a trifunctional monomer which unde rgoes a polycondensation reaction is presented. Both components contri bute with an excess volume, calculated according to Simha and Boyer co ncepts. The free energy of mixing, stated in a lattice model, includes the contribution of holes in both entropic and enthalpic terms. The c ure shrinkage is simulated through a decrease in the Van der Waals vol ume (and the associated excess volume) of the thermosetting polymer wi th conversion. This leads to a decrease in the absolute value of the 0 entropic contribution and an increase in the value of the term associ ated with interaction energies. Both factors act against rubber miscib ility, thus leading to demixing at lower conversions (compared to the case where cure shrinkage is excluded). The effect is, however, relati vely small. (C) 1997 Elsevier Science Ltd.