engleski

Kinetics of Epoxy Curing Reactions during Organic-Inorganic Hybrid Formation

Kinetics of epoxy group reactions during organic-inorganic hybrid formation, by the sol-gel process, was studied by means of differential scanning calorimetry (DSC). Simultaneous polymerization of a thermoset epoxy resin, diglycidyl ether of bisphenol A (DGEBA) and an inorganic precursor, 3-glycidyloxypropyltrimethoxysilane (GLYMO), was performed using poly(oxypropylene) diamine (JEFFAMINE) as a curing agent. Curing was effected at room temperature (from 0 to 5 hours) making use of air humidity for hydrolyzing GLYMO. The (post)curing of the investigated systems: DGEBA/JEFFAMINE; GLYMO/JEFFAMINE and their mixture in weight ratio of 50/50 (G1E1) was performed in DSC cell in isothermal conditions at different temperatures and in dynamic conditions at two different heating rates. DSC results suggest that in the DGEBA/JEFFAMINE system the primary and secondary amines are of equal reactivity. In the GLYMO/JEFFAMINE system the reaction of secondary amines and epoxide is negligible. At the very beginning of the sol-gel process for the hybrid system G1E1 the comparable total heat of reaction, developed during simultaneous polymerization in dynamic DSC tests, to the theoretical value, based on the total heats developed during DGEBA/JEFFAMINE network formation and GLYMO/JEFFAMINE reaction, was found. It is very probable that investigated hybrid materials are organic-inorganic interpenetrating polymer networks. The isothermal DSC results indicated that as the sol-gel process preceded the silanol groups formed by the hydrolysis of the methoxy groups of GLYMO provided a favorably catalytic environment for epoxy-amine reactions. The kinetics of reactions was described by empirical models. The kinetics of DGEBA/JEFFAMINE system was described by an autocatalyzed reaction mechanism. For the hybrid G1E1 system the reaction rate was best described by nth order kinetics. Kinetic models, with parameters determined from isothermal DSC data, was successfully applied to dynamic DSC data.

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