THE EPOXY-POLYCARBONATE BLENDS CURED WITH ALIPHATIC AMINE .2. THERMALAND MECHANICAL-PROPERTIES MECHANISMS

The transamidation reaction converts the carbonate and amine into N-al iphatic aromatic carbamate and urea, causing the equivalent of oxirane and amine nonstoichiometric in the primary cure stage. After postcure , the substitution reaction takes place and results in a more tightly crosslinked structure. Such a higher crosslinking density is responsib le for higher T-g, tensile strength, and tensile modulus in the postcu re stage than that in the primary and secondary cure stages. This tren d is more pronounced in those PC-epoxy blends containing higher molecu lar weight aliphatic amine or a higher content of PC. This phenomenon is due to the difference in the fraction of amino group of aliphatic a mine consumed in the transamidation. PC-epoxy/aliphatic amine blends s how minor improvement in the high strain rate Izod impact tests, while toughness improvement for some blends is substantial at low strain ra te tensile tests. (C) 1997 John Wiley & Sons, Inc.