Interphase Transfer of Tackifier between Immiscible Rubbers

Interphase transfer of a coumarone-indene tackifier between natural rubber (NR) and poly(isobutylene) (PIB) was studied. The laminated sheets, composed of a sheet of NR with the tackifier and a sheet of PIB with the tackifier, were annealed at various temperatures to promote the interphase transfer of the tackifier. After separating the two sheets, the infrared spectra were measured to evaluate the tackifier content in each rubber sheet. It was found that a large amount of the tackifier resided in PIB after annealing at ?20°C, whereas the tackifier moved to NR at 40°C. Consequently, the NR sheet exhibited a lower glass transition temperature T_g after annealing at ?20°C and a higher T_g when annealed at 40°C. The differential scanning calorimetry measurements revealed that the crystallization of NR was responsible for the tackifier transfer. This phenomenon should be of interest because the tackifier transfer, which results in the T_g shift of each rubber, would also occur in a blend system. When NR is the matrix of the blend, it would be an ideal blend because the matrix would show a low T_g in winter and a high T_g in summer.