1989 Volume 17 Issue 3 Pages 155-161
Dynamic viscoelastic responses were explored on isotactic polypropylene (i-PP) melt (Mv=1.61×105, Mw/Mn=4.4) and 1% 1, 3; 2, 4-p, p′-ditoluyliden sorbitol (PDTS)/i-PP system in order to investigate sol-gel transition of PDTS in polymeric media. The storage modulus G′ and the dynamic viscosity η′ were obtained as a function of temperature in the cooling process from 250 to 130°C for i-PP and from 250 to 150°C for PDTS/ i-PP system at angular frequencies of 10-4, 1, 10, 102rad/s. The results indicated that 1% PDTS/i-PP system has a sol-gel transition temperature Tfg=201°C, which is identified as the critical temperature for formation of the PDTS percolation network.
The master curves of G′ and η′ are obtained for the sol and gel regions of 1% PDTS/ i-PP system assuming the thermorheological simplicity in each region. The master curves for the sol region of 1% PDTS/i-PP system are found to be nearly identical with those of the bulk i-PP melt. However, they were found to be quite different from those for the gel region, especially at low frequencies (corresponding to the terminal flow region of the sol); the gel exhibited a significant increase of η′ and a plateau in G′ curve, as well. The loss tangent, tanδ, for the gel was around 1 in the whole frequency range measured. These results for the gel imply that (i) the PDTS aggregates into a percolation network of a large spatial scale, and that (ii) the association of the dissolved PDTS in the matrix into the networks and the dissociation of the PDTS molecules in the networks into the matrix are in dynamical equilibrium, giving rise to the large tanδ. A model of the sol-gel transition was presented.
