Stability of PMR-Polyimide Monomer Solutions

The stability of alcohol solutions of norbornenyl capped PMR-polyimide resins (both PMR-15 and PMR-II) has been monitored during storage at ambient and subambient (5 deg C and -18 deg C) temperatures. Chemical changes during storage were determined spectroscopically using nuclear magnetic resonance. Resin processability and cured resin quality were determined by fabrication of unidirectional, graphite fiber composites using aged solutions and testing of selected composite properties. PMR-15 solutions exhibit nominally two weeks of useful life and PMR-II solutions exhibit nominally two days of useful life at ambient conditions. The limiting factor is precipitation of imide reaction products from the monomer solutions. Both solutions exhibit substantially longer useful lifetimes in subambient storage. PMR-15 shows no precipitation after several months storage at subambient temperatures. PMR-II solutions do exhibit precipitates after extended subambient storage (nominally three months at -18 deg C), however, the precipitates formed under these conditions can be redissolved. The chemical implications of these observations are discussed. jg p2 Presented at Annual Conference of SPI Reinforced Plastics/Composites Institute (34th), January 29 - February 2, 1979, New Orleans, Louisiana.