Effect of chemical structure on the crosslinking behavior of bismaleimides: Rheological study |
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Authors: | Jung Ok Park Beom-Jin YoonMohan Srinivasarao |
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Affiliation: | a School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA b Center for Advanced Research on Optical Microscopy, Georgia Institute of Technology, Atlanta, GA 30332, USA c School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA |
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Abstract: | The effect of molecular structure on the cure characteristics of bismaleimides (BMIs) was investigated by rheological measurements. BMI resins of different chemical structures were used, prepared from diglycidyl ether of bisphenol A and N-(3-carboxy phenyl) maleimide or N-(4-carboxy phenyl) maleimide. Temperature dependence of the rheological data was correlated to the Arrhenius equation, from which the activation energy of crosslinking was calculated.Upon heating in dynamic curing, viscosity passed through a minimum then sharply increased due to increasing amount of the crosslinking reaction. The temperature at minimum viscosity increased as the chain length became longer. After passing the minimum point, viscosity increased much faster for meta BMIs (3BE1, 3BE2) than para BMIs, however, the difference in the chain length did not show any appreciable difference in the viscosity increase rate (dη∗/dT). Nonetheless, the final viscosity was lower for longer chains, because their crosslinking density would be lower.In isothermal curing, the final crosslinking density was expected to increase with temperature, which was shown via the increase in the final viscosity. The gelation time decreased with temperature, and the activation energy of the crosslinking reaction was obtained. Using the reaction kinetics parameters obtained from dynamic scanning calorimeter and Arrhenius type equation, the viscosity change during the isothermal curing was simulated and compared with the measurements. |
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Keywords: | Bismaleimide (BMI) Chemorheology Crosslinking kinetics Viscosity Gelation Activation energy |
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