Nonstoichiometric condensation

The rate of this reaction is about ten times smaller than that of Eq. (I) and under typical cure conditions it becomes noticeable only after the end of the main process. Scheme (II) changes the structure of networks by the formation of additional crosslinks of the ether type. This makes the total connectivity of the network higher. This structural change influences some properties of polymers in the glassy and rubbery state (see Sects. 4 and 5), but it is really pronounced in nonstoichiometric systems with an excess (P < 0.8) of epoxy components 19,22). Crosslinks of the ether type may principally appear in polymers due to a condensation reaction between OH groups. Under our conditions this process normally does not take place. 

Upon condensation, a high activation energy is necessary in order to dissociate the gaseous species, such as N2, S2, Chj, As+Og, P4. If such an energy is not provided, nonstoichiometric deposits, such as MeNj CdSi EuChj or metastable modifications, P4 (s, white), As40g (Arsenolite), result. In some cases both the evaporation and condensation can be facilitated by proper catalysts. Some examples are... 

Every cmidensed phase of compounds shows some extent of nonstoichiometiy, the deviation from its nominal stoichiometric compositimi. It comes from the thermod3mamic nature of condensed phase and thus comprehensive. That is, there is no compound phase without nonstoichiometric compositional deviations [1]. 

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