MELT RHEOLOGY OF A CLASS OF POLYESTER IONOMERS

The rheological response of a class of random polyester ionomers was investigated over a wide range of compositions and temperatures. The ionomers are derived from poly(ethylene terephthalate) (PET) modified through copolycondensation with a fully neutralized sulfonate moiety, (sodiosulfo)isophthalate (SIP). Isothermal and isochronous measurements, over a temperature range spanning from the glass-transition to the terminal zone, were conducted using oscillatory and steady-state techniques. Significant and systematic increases in melt viscosity and flow activation on addition of SIP to the PET backbone were observed, indicating strong association and a high degree of aggregation of the ionic species. At SIP levels >10 mol %, the time-temperature superposition rule was found to break down, suggesting the presence of phase-separated, large ionic domains (clusters) within the organic matrix, although no evidence for a second (cluster) glass transition was noted. Increase in SIP concentration also led to a significant increase in the plateau modulus and to substantial broadening of the glass-transition range of the host polymer. The experimental data are discussed in the context of the restricted mobility model of Eisenberg and co-workers.25