To gain insight into the physical and chemical effects during the linear chain and network formation, dielectric properties of four diepoxide-amine liquid mixtures have been studied during their polymerization at pressure raised from 1 bar to 200 bar in an upstep, and after a predetermined period lowered to 1 bar in a downstep manner, many times during the course of polymerization. For comparison, dielectric properties were also studied when the samples were maintained at a fixed 1 bar pressure or at 200 bar pressure. Although pressure is expected to decrease the polymerization rate for all conditions, the decrease was observed only when polymerization became diffusion-controlled. In the early stages, effects other than the viscosity＇s increase on compression dominate the dielectric behavior. An analysis by mathematical simulation shows that both physical and chemical effects of pressure steps are significant, but their relative magnitudes vary during the course of polymerization. A pressure upstep also increased the sample＇s temperature, and a downstep decreased it, after which the temperature reached the equilibrium value asymptotically. This effect was also evident in the time dependence of the dielectric properties and was found to be consistent with the effects of temperature observed before. The study demonstrates the validity of the various concepts used for the pressure and temperature effects on the negative feedback effects between molecular diffusion and chemical reaction during a macromolecule＇s growth.