Epoxy network formation

Detailed discussions of network formation from amines and epoxy resins are provided in References 24 and 25. 

DuSek, K. Network Formation in Curing of Epoxy Resins. Vol. 78, pp. 1—58. 

Figure 7.37 Network formation of phenolic novolac and epoxy.

Negative neighboring group effect, 456 Network formation, 13 Networks. See also Epoxy-phenol networks Phenohc networks phenolic-based, 376 polyester-based, 58-60 Neutral hydrolysis, 564-565... 

In the foregoing considerations, formation of elastically inactive cycles and their effect have not been considered. For epoxy networks, the formation of EIC was very low due to the stiffness of units and could not been detected experimentally the gel point conversion did not depend on dilution in the range 0-60% solvent therefore, the wastage of bonds in EIC was neglected. For polyurethanes, the extent of cyclization was determined from the dependence on dilution of the critical molar ratio [OH] /[NCO] necessary for gelation (25) and this value was used for the statistical calculation of the fraction of EIC and its effect on Ve as described in (16). The calculation has shown that the fraction of bonds wasted in EIC was 2-2.5% and 1.5-2% for network from LHT-240 and LG-56 triols, respectively. 

The previous discussion has shown that the CIPS technique allows one to produce macroporous epoxy networks with either a narrow or bimodal size distribution. However, no indication has been given on the type of phase separation mechanism to yield these morphologies. As discussed earlier, the formation of a closed cell morphology can result either from a nucleation and growth mechanism or from spinodal decomposition. 

Low-molecular-weight model compounds such as phenylglycidyl or other mono-glycidyl ethers as well as primary, secondary and tertiary amines have been used for the study of the kinetics, thermodynamics and mechanism of curing. To reveal the kinetic features of network formation, results of studies of the real epoxy-amine systems have also been considered. Another problem under discussion is the effect of the kinetic peculiarities of formation of the epoxy-amine polymers on their structure and properties. 

A key problem in the kinetics of the reactions under study is a relation between the rate constants of the epoxy ring opening under the effect of the primary and secondary amino groups, i.e. manifestation of the substitution effect. This problem has been briefly reviewed by Dusek64>. Knowledge of the relationship between these rate constants is very important for an adequate description of the kinetics of network formation. It should be emphasized that knowledge of such a relation, rather than the absolute values of the rate constants would be sufficient. 

The epoxy/siloxane/PACM-20 mixture was poured into a hot (120 °C) RTV-silicone mold of the precise shapes to be used for solid-state testing. The mixture was cured at 160 °C for 2.5 hours. The curing time and temperature chosen were considered to provide enough mobility for network formation. This conclusion was partially based on earlier studies which found a glass transition temperature of 150 °C for Epon 828/PACM-20 3S). 

This may not be the case if during the network formation there are two (or more) possible reaction paths in competition e.g., epoxy networks obtained using dicyandiamide as hardener (Amdouni et al., 1990). 

The simultaneous formation of the polyimide and the three dimensional epoxy network occurs because of the polyamic acid containing reactive groups that can initially open the oxirane groups of the DGEBA and then subsequently intramolecularly cyclize to become polyimide as the epoxy network extends. These reactions are summarized in Fig. 4. 

Network Formation in Curing of Epoxy Resins (Part III, Vol. 78). T. Kamon and H. Furukawa (The Kyoto Municipal Research Institute of Industry, Kyoto, Japan). 

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