HIGH-FLOW ADDITION CURING POLYIMIDES

A new series of high flow PMR-type addition curing polyimides was deve loped, which employed the substitution of 2,2'-bis(trifluoromethyl)-4, 4'-diaminobiphenyl (BTDB) for p-phenylenediamine (p-PDA) in a PMR-II f ormulation. These thermoset polyimides, designated as 12F resins, were prepared from BTDB and the dimethyl ester of 4,4'-(hexafluoroisopropy lidene)-diphthalic acid (HFDE) with either nadic ester (NE) or p-amino styrene (PAS) as the endcaps for addition curing. The 12F prepolymers displayed lower melting temperatures in DSC analysis, and higher melt flow in rheological studies than the corresponding PMR-II polyimides. Long-term isothermal aging studies showed that BTDB-based 12F resins e xhibited comparable thermo-oxidative stability to p-PDA based PMR-II p olyimides. The noncoplanar 2- and 2'-disubstituted biphenyldiamine (BT DB) not only lowered the melt viscosities of 12F prepolymers, but also retained reasonable thermal stability of the cured resins. The 12F po lyimide resin with p-aminostyrene endcaps showed the best promise for long-term, high-temperature application at 343-degrees-C (650-degrees- F). (C) 1994 John Wiley & Sons, Inc.