Nadic_Pyromellitic_BisA_epoxidema0492925 - Macromolecules...

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Chemical/Mechanical Analyses of Anhydride-Cured Thermosetting Epoxys: DGEBA/NMA/BDMA Wei Chian ² and Delmar C. Timm* Department of Chemistry and Chemical Engineering, South Dakota School of Mines, Rapid City, South Dakota 57701, and Department of Chemical Engineering, University of Nebraska s Lincoln, Lincoln, Nebraska 68588 Received April 12, 2004; Revised Manuscript Received July 14, 2004 ABSTRACT: The chemical state of cure in a thermosetting resin was used to predict the resin’s equilibrium modulus. High performance liquid chromatography analyses of the sol fraction yielded molar dynamics for monomeric, oligomeric, and polymeric molecules. Their population density distributions were compared with theoretical predictions based on a chain-growth polymerization mechanism. The resulting chemical estimates of the state of cure were integrated into calculations yielding concentrations of network structures within the gel that contribute to the density of elastically active strands and junctions. The theory of rubber elasticity was then used to predict the equilibrium modulus. Measurements incorporated dynamic mechanical analysis. A comprehensive understanding of the polymerization mechanism and cure history are required for accurate simulations of contributions from branch nodes and chain links. Deterministic models based solely on chemical reaction analysis were used to estimate chain connectivity with the gel. Results were interpreted using stochastic-based reasoning. Introduction Research integrated cure dynamics associated with chain structure into predictions of a thermosetting resin’s equilibrium modulus. 1,2 The anhydride cured epoxy studied is used as a matrix in high performance, fiber-reinforced composites featuring high specific strength and stiffness and good thermal stability. At elevated temperatures and at high levels of compressive stress at ambient temperature, the molecular structure of the matrix is fundamental to its mechanical proper- ties, which in turn contribute to the performance of the composite. During the major portion of a cure based on the diglycidyl ether of Bisphenol A (DGEBA), methyl-5- norbornene-2,3-dicarboxylic anhydride, or nadic methyl anhydride (NMA) with the tertiary amine catalyst benzyl dimethylamine (BDMA), Antoon and Koenig 3 observed chemical intermediates that participate in the polymerization reactions. Polyether formation is absent when both monomers are present. Nielsen et al . 4 and Tadros and Timm 5 simplified published reaction schemes to a chain-growth polymerization mechanism where an initiator supplies propagation sites which react with monomers in chain-wise reactions and with oxiranes on molecules in the resin yielding branched and, ulti- mately, cross-linked chains. Molecules of a similar chemical structure regarding molecular weight and reactive groups were lumped into the dependent vari- able.
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This note was uploaded on 07/20/2011 for the course EMA 6165 taught by Professor Brennan during the Spring '08 term at University of Florida.

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Nadic_Pyromellitic_BisA_epoxidema0492925 - Macromolecules...

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