Molecular Weight Effects on the Processing, Thermal, and Mechanical Properties of Oligomeric Bisphenol a Phthalonitrile Resins

Abstract

Oligomeric phthalonitrile (PN) resins are desirable materials for many high-temperature applications because they exhibit good structural performance over a large temperature range, have low thermal conductivity and water absorption, as well as excellent fire performance. However, integration of these materials into certain high temperature applications has been impeded because of their limited long term oxidative stability. This is due to the high stiffness of PN resins which makes them susceptible to microcracking at elevated operating temperatures. One strategy to prevent microcracking is to improve resin flexibility by increasing its molecular weight. Along these lines, a series of bisphenol A PN resins (BisA) were synthesized with varying molecular weights. The thermal and rheological properties of each resin were characterized in order to determine the optimum processing conditions for producing void free samples of the cured resins. These samples were then subjected to a series of measurements to probe molecular weight effects on the thermal and mechanical properties of the BisA resins. Long term oxidative studies were conducted by measuring the mass of these samples before and after heating at 300 °C for 1000 hours. Samples were also imaged to probe the presence of heating induced microcracking of BisA resins.