Kinetic and mechanical analysis of anhydride -cured linear and non-linear epoxies

The anhydride cure of epoxy resins was studied experimentally. First, an amorphous, thermoplastic resin formulated with phenyl glycidyl ether (PGE), nadic methyl anhydride (NMA) and the catalyst benzyldimethylamine (BDMA) was investigated. Oligomeric species were synthesized and fractionated by reversed phase high performance liquid chromatography (HPLC). Molecular dynamics was traced by the measurement of population density distribution (PDD) as a function of the conversion of oxirane moieties. Kinetic data interpretation yielded distinct rate constants for initiation and propagation reactions, which caused a PDD narrower than the Poisson molar distribution. Fourier transform infrared (FTIR) spectroscopy proved that the ester forming propagation reactions were dominant. Polymeric kinetics of the thermoplastic resin was also attacked using multiple angle laser light scattering with gel permeation chromatography (GPC-MALLS). Experimental-theoretical comparison of the molecular size distributions and moment analysis revealed the presence of secondary reactions when the concentration of alcoholic initiator is low. Based on molecular insight gained from the experimental investigation on the linear analog, attention was then directed to a diglycidyl ether of bisphenol A (DGEBA) based thermoset DGEBA/NMA/BDMA. Molecular characterization of the sol fraction was performed using GPC-MALLS. Observed kinetic reaction information provided a basis for rigorous examination of the kinetic reaction model and was also used in a molecular feedback sense along with the sol/gel partition measurements for the description of chain topology within the insoluble gel fraction (crosslinking density and concentration of permanent entanglements etc.) as a function of extent of cure. This ultimately enabled the prediction of the equilibrium modulus at elevated temperatures. Results in this regard when evaluated with the viscoelastic properties measured with the aide of dynamic mechanical thermal analysis (DMTA) offered an examination of the applicability of the rubber elasticity theory to this anhydride cured thermosetting epoxy