THE EPOXY-POLYCARBONATE BLENDS CURED WITH ALIPHATIC AMINE .1. MECHANISM AND KINETICS

Reaction mechanism of the PC-epoxy blends cured by aliphatic amine has been investigated by varying PC contents in the blends. The transamid ation reaction tends to convert nearly all the carbonates into N-aliph atic aromatic carbamates even at ambient temperature before normal cur ing. The remaining amine proceeds the normal curing with epoxy at a hi gher temperature (80 degrees C). For the PC-epoxy/aliphatic amine blen d containing 6 wt % PC, the yielded N-aliphatic aromatic carbamate fur ther reacts with amine to produce the urea structure. The urea undergo es substitution reaction with the hydroxyl formed from the normal curi ng to give the N-aliphatic aliphatic carbamate. For the blend containi ng 12 wt % PC, the N-aliphatic aromatic carbamate converts into the N- aliphatic aliphatic carbamate via two different routes. For the blend containing lower molecular weight of the aliphatic amine, the N-alipha tic aromatic carbamate reacts with hydroxyl to form the N-aliphatic al iphatic carbamate directly. For the blend containing higher molecular weight of aliphatic amine, the N-aliphatic aromatic carbamate decompos es into the aliphatic isocyanate accelerated by the presence of the re sidual oxirane. The isocyanate formed then reacts with hydroxyl to yie ld the N-aliphatic aliphatic carbamate. The activation energy (E-alpha ) and preexponential factor (A) of the PC-epoxy/POPDA blends decrease with the increase of the PC content. Kinetic study by thermal analysis by the method of autocatalyzed model is able to correctly predict oxi rane conversion vs. time relationship for the neat epoxy/aliphatic ami ne and the PC-epoxy/aromatic amine systems because the dominant reacti on is the normal curing reaction between amine and oxirane. The model fails to predict the PC-epoxy/aliphatic amine system because the syste m is complicated by several other reactions besides the normal curing reaction. (C) 1997 John Wiley & Sons, Inc.