Rheology of oligomer curing

Abstract

The present state of the art of investigations on the rheological properties of oligomers being cured is discussed. The correlation between two rheological criteria for reaching the gel point — the loss of fluidity and the maximum of mechanical losses — is shown. The concept of “rheological” degree of conversion which correlates to a predetermined degree derived by the calorimetric method is introduced. The gel point is reached at various “rheological” degrees of curing. A phenomenological kinetic equation of the self-acceleration type is suggested for the time dependence of the storage modulus. The constants of this equation depend on the temperature and concentration of the reagents in the system. When passing from a low-functional to a polyfunctional curing agent, self-acceleration changes to self-deceleration, which is connected with topological difficulties and leads to incomplete curing.

For the “stepwise” model of the changes in the viscosity during curing it has been shown that deformation does not play a “kinetic” role, but influences the reduction of the period to retain the fluidity through dissipative heating of the reaction mass in the flow.