PHYSICS OF LINEAR-CHAIN AND NETWORK POLYMERIZATION BY DIELECTRIC-SPECTROSCOPY

Dielectric relaxation spectroscopy has been used to investigate what h appens when a monomeric, molecular liquid polymerizes isothermally to form either a linear chain polymer or a network structure. Polymerizat ion was done by using a diepoxide molecule which after reaction with a niline formed a linear chain polymer and a triepoxide which after a si milar reaction formed a molecular network structure. The dielectric pe rmittivity and loss were measured as a function of reaction time for 2 4 ac frequencies (10Hz-10(5)Hz) and the data interpolated to obtain th e relaxation spectra for several apparently fixed reaction times. Thes e results are then analyzed in terms of the dependence of the dielectr ic behaviour on the number of covalent bonds formed as polymerization progressed. The dc conductivity for the linear chain polymerization va ried with time in a manner quite different from that for network polym erization. In the latter case, the data followed an equation usually s een as a characteristic of gel-formation. The relaxation time determin ed from the fixed frequency measurement as the reaction progressed agr eed with the relaxation time determined from the dielectric spectra in terpolated for apparently fixed states at any instant during the polym erization. These results are interpreted in terms of a decrease in the configurational entropy. As polymerization progressed, both the stati c and the limiting high frequency permittivity decreased and a faster relaxation process evolved as the polymerization approached completion . It is concluded that the number of covalent bonds formed on polymeri zation and the temperature can be varied in a manner such as to mainta in the relaxation time of the state (with same chemical constituents) at the same value. This equivalence of number of bonds and the tempera ture should be seen as fundamental to the relaxation behaviour.