Thermokinetics and chemorheology of the cure reactions of the tetraglycidyl diamino diphenyl methane–diamino diphenyl sulfone epoxy systems

Abstract

SynopsisThe cure behavior of commercial grade TGDDM-DDS mixtures of compositions ranging from 1 0 10 100 phr of hardener and the thermal polymerization of the epoxy component are analyzed by means of' differential scanning calorimetry. The kinetic parameters and heats of reaction determined in isothermal and dynamic scans suggest that DDS primary amine addition and epoxide etherification dominate the cure reactions. The primary amine epoxide addition is characterized by overall heat of'reaction (referred to the weight of the epoxy component) of 255 cal/g and by an activation energy 01' 16.6 kcal/mol. The corresponding values for the etherif'ication reaction are, respectively, 170 cal/g iind 41 kcal/mol. A method of derivation of the epoxide conversion from the heat evolved in DSC thermal scans of these systems is presented. The results are in good agreement with independent IK determinations. The steady shear and oscillatory viscosity measurements and the calorimetric iinalysis of the isothermal cure a t 14OoC, 160"C, and 180°C of a TGDDM-DDS mixture containing :i5 phr of' hardener indicate that gelation is principally governed by the piimary amine addition. The gelation limits calculated in isothermal tests by combining the calorimetric analysis and the theory describing the nonlinear copolymerization of the tetrafunctional TGDDM with an essentially difunctional DDS were in good agreement with the values experimentally determined through rheological measurements.

Rheological behaviour of a commercial TGDDM-DDS based epoxy matrix during the isothermal cure

“…By plotting the critical times as a function of the temperature in an Arrhenius diagram, figure 7, an activation energy of the cure process of 19.7 Kcal/mole has been determinated. Previous calorimetric tests [8] performed on the same mixture indicates that the reactive system was initially characterized by an activation energy of 19.0 Kcal/mole, which favourable compares with the previous rheological determination. As suggested in the already mentioned work, the early stages of the cure process involves an epoxy ring opening following the electrophilic attack by the primary amine to form an amino-alcohol, in fact the activation energy of this process is 16.6 Kcal/mole while the corresponding value for the etherifications is 41 Kcal/mole.…”

“…The ranges investigated were from 1% to 50% strain amplitude and from 0.1 to 100 Hertz frequency. Figures 1 and 2 indicate that the reactive mixture, tested at temperatures where the kinetics of the cure reactions is too low to influence the actual molecular distribution [6,8] exhibits linear viscoelastic behaviour on the overall ranges investigated. Further tests indicates that the influence of the cure kinetics on the rheological behaviour becomes appreciable only above 120 °C.…”

Synthesis, Curing, and Properties of an Epoxy Resin Derived from Gallic Acid

“…Table 1 also reports the heat of reaction per mole, obtained using an average value of EEW= 104.89 g/equiv. The molar heat of reaction obtained for amine cured GEGA is only slightly higher than those found in the literature for amine addition to tetra-and diepoxides, usually between 45 and 50 kJ/mol (Apicella et al 1984;Nunez et al 1999;Swier et al 2004). The slight difference in peak temperatures could be explained by the lower steric hindrance of the cyclic amine compared with polyether.…”

Nonisothermal cure kinetics of DGEBA with 2,7‐diaminofluorene

“…T g for the samples containing 26 and 36 phr DAF were found to be 144 and 153 C, respectively. The E a values obtained in this study by KAS and Ozawa methods (55.68 and 58.27 kJ/mol, respectively) are almost in the same range of the E a values reported by other workers [6][7][8][9]29,30 for epoxy-diamine systems (45-65 kJ/mol). DSC analysis has shown 29 that etherification occurs at elevated temperatures once all the primary amines are exhausted.…”