Formation of Junction Zones in Thermoreversible Gelation Process of Ethylene-Propylene Random Copolymer/Toluene Systems

Abstract

Melting behaviour of ethylene-propylene random copolymer (EP random copolymer)/toluene thermoreversible gels was measured by the falling ball method (FBM) and differential scanning calorimetry (DSC). By applying the theory proposed by Takahashi, Nakamura and Kagawa (Takahashi theory) to the gel melting temperature T^g_m measured by FBM, values of number of monomers ξ per chain in a junction point were evaluated. Further, values of ζ and s were evaluated by the Tanaka theory. ζ in Tanaka theory has the same physical meaning as ξ in Takahashi theory and s means the number of polymer chains contained in a junction point. The obtained values of ζ have the same order of magnitude but smaller than ξ. In DSC measurements, the enthalpy of melting (ΔH_m) of junction points was measured. ΔH_m increases with the increase of gelation time, and then approaches a constant value. The gelation time t_h, which is necessary to reach the equilibrium value of ΔH_m, is extremely longer than the gelation time t_m, which is necessary to obtain a constant value of T^g_m.