Investigation of readily processable thermoplastic-toughened thermosets: IV. BMIs toughened with hyperbranched polyester

✍ Scribed by A. Gopala; H. Wu; J. Xu; P. Heiden

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 231 KB
• Volume: 71
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/(sici)1097-4628(19990314)71:11<1809::aid-app10>3.0.co;2-k

✦ Synopsis

This is the fourth article in a series describing efforts to produce tough, high-performance thermosets from very low viscosity prepolymers which are autoclave processable. Hydroxy-terminated hyperbranched polyester (HBP) with a systematically increased molar mass was used to toughen bismaleimide (BMI). HBP was dissolved in the allyl phenol component, B, of a two-part BMI, to yield homogeneous solutions. The BMI monomer, A, was dissolved in the solution of HBP in B to give homogeneous prepolymers. The fracture toughness (K Ic ) of neat resin plaques was measured by compact tension, while the T g and storage moduli (EЈ, at 55 and 200°C) were determined by DMA. At 9% loading, the K Ic of the BMI increased steadily with HBP molecular weight up to 138% over the control with G5 HBP (M n ϳ 14,000 g/mol); however, significant decreases in both the T g and EЈ resulted, indicating incomplete phase separation of the thermoplastic. A linear hydroxy-terminated polyester (M n ϳ 5400 g/mol) with a repeat unit structure which was similar to the HBP's was prepared and used as a control. The linear polyester (LPE) toughened the BMI nearly as effectively as did the HBP and caused a smaller decrease in the T g and EЈ. The viscosity of solutions of HBP and LPE in B were essentially the same at lower loadings in B, but at higher loadings, the HBP viscosity increased faster than did that of the LPE. The viscosity increase was end group-dependent. Preliminary morphological results are presented to show the effect of the thermoplastic architecture, loading, and end group on the cured thermoset.