INVESTIGATION OF READILY PROCESSABLE THERMOPLASTIC-TOUGHENED THERMOSETS - I - BMI TOUGHENED VIA A REACTIVE SOLVENT APPROACH

Moderate increases (similar to 50-75%) in the toughness of bismaleimid es (BMIs) were achieved with very low-molecular-weight (similar to 100 0 g/mol) imide thermoplastics at low levels of thermoplastic loading ( similar to 10-20%). The thermoplastic was introduced into the BMI usin g a simple, one-pot, reactive solvent approach. In this approach, the reactive diluent of a two-part BMI was used as the reaction solvent fo r the thermoplastic synthesis. The BMI monomer was then dissolved in t he thermoplastic reaction solution to yield a low-viscosity homogenous prepolymer. The viscosity of the thermoplastic solution was similar t o 6 Pa S at 55 degrees C. The effect of thermoplastic loading and mole cular weight on viscosity was determined by rheology, and the fracture toughness of neat resin plaques was determined by compact tension. In creasing the thermoplastic loading increased prepolymer viscosity with out improving toughness, while increasing the thermoplastic molecular weight increased the toughness by only 25% more than the lowest-molecu lar-weight thermoplastic, yet increased viscosity fivefold. Fracture s urfaces showed no obvious phase separation by scanning electron micros copy. (C) 1998 John Wiley & Sons, Inc.