Investigation of Readily Processable Thermoplastic-Toughened Thermosets: IV. BMIs Toughened with Hyperbranched Polyester
Department of Chemistry
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 (KIc) of neat resin plaques was measured by compact tension, while the Tg and storage moduli (E′, at 55 and 200°C) were determined by DMA. At 9% loading, the KIc of the BMI increased steadily with HBP molecular weight up to 138% over the control with G5 HBP (Mn ∼ 14,000 g/mol); however, significant decreases in both the Tg and E′ resulted, indicating incomplete phase separation of the thermoplastic. A linear hydroxy-terminated polyester (Mn ∼ 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 Tg and E′. 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.
Journal of Applied Polymer Science
Investigation of Readily Processable Thermoplastic-Toughened Thermosets: IV. BMIs Toughened with Hyperbranched Polyester.
Journal of Applied Polymer Science,
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