Long-Branched Structure of Polybutadienes Analyzed by Rheology

Abstract

The linear and nonlinear viscoelastic properties of five polybutadienes (PBs: Y1, Y2, V, Co1, and Co2) synthesized using three different catalysts and two processes were measured to investigate their molecular structures, with a focus on long-branched structures. Concentrated PB solutions (10 %, 30 %, 50 %) were prepared with liquid paraffin as the solvent. The storage modulus G′ and loss modulus G″ of the PB solutions and PB melts were measured. The relationships between G′c⁻² and G″c⁻² corrected by concentration (c) are strongly dependent on the presence or absence of long branches in PBs. At G″c⁻² = 20,000 Pa, the value of G′c⁻² for long-branched PBs increases with PB concentration, and also increases for more complex long-branched structures. The values of G′c⁻² for Y2 and V were not dependent on concentration. The results showed that Y2 and V have linear molecular structures and that Y1, Co1, and Co2 have long-branched structures, with the order of complexity being Y1 > Co1 > Co2. From the damping functions evaluated by large-deformation stress relaxation measurements of the 30 % PB solutions, the order of long-branched structural complexity was Y1 > Co1 > Co2 > V ≈ Y2. This order was essentially the same as that based on the linear viscoelasticity of the PB samples. The rheological method in this study provides structural information about long-branched PBs.