POLYMER NETWORKS DERIVED FROM THE ANHYDRIDE CURING OF TETRAEPOXIDES

The cure of a technical-grade TGDDM ,N,N'N'-tetraglycidyl-4,4'-diamino diphenyhnethane) with two different anhydride hardeners (hexahydrophth alic anhydride [HHPA] and tetrahydrophthalic anhydride [THPA]) is repo rted. The reaction was followed by differential scanning calorimetry ( DSC), in situ infrared spectroscopy (FTIR), and viscosity measurements at constant temperature. Onset values of the glass transition tempera tures of fully reacted networks under stoichiometric conditions were 2 06 degrees C with HHPA and 184 degrees C with THPA. THPA was more reac tive than was HHPA but it was necessary to heat the mixture above its melting point to generate a homogeneous solution (HHPA remained in sol ution at room temperature). A first-order kinetics was observed after an induction period necessary to establish a pseudo-steady-state conce ntration of OH and COOH groups. A catalytic effect of the I(Br used in the FTIR measurements was found, in agreement with other authors. For mulations containing an epoxy excess exhibited a higher reactivity due to the increase in the hydroxyl concentration introduced by the epoxy monomer. An increase in the heat of reaction expressed per anhydride equivalent was ascribed to the presence of the epoxy homopolymerizatio n as a side reaction. It was estimated that about 38% of excess epoxy groups over the anhydride groups are homopolymerized in the case of HH PA and 17% in the case of THPA. Full conversions of both epoxy and anh ydride groups are obtained for formulations with stoichiometric ratios , r (anhydride/epoxy groups) = 0.72 in the case of HHPA and 0.85 in th e case of THPA. These values are in the range where the maximum glass transition temperature has been reported for epoxy-anhydride formulati ons. (C) 1997 John Wiley & Sons, Inc.