A series of narrow molecular weight distribution carboxy-telechelic vinyl polyisoprenes of molecular weight 8000, neutralized with Ca2+, Sr2+, Ni2+, Zn2+, and Cd2+, are examined by several techniques. The small-strain tensile moduli of these materials are found to be significantly higher than predicted on the basis of the contribution of ionic aggregates acting as physical cross-links and fillers, with the Ca2+ and Sr2+ ionomers having the highest moduli. The modulus enhancement is attributed to entanglements, in the form of interlocking loops formed when both ends of a telechelic chain reside in the same aggregate. Small-angle X-ray scattering reveals that the Ca2+ and Sr2+ materials have larger aggregates and therefore more trapped entanglements and higher moduli. Strain-hardening behavior is observed for the Ca2+ and Ni2+ telechelics, but not in the other three materials. Extended X-ray absorption fine structure spectroscopy shows that these two materials have more ordered ionic microdomains, making ion hopping more difficult. The Ca2+ and Ni2+ telechelics strain-harden and break when the interlocking loops pull taut, whereas stressed entanglements in the other telechelics can relax by pulling ionic chain ends out of the aggregates.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics
- Inorganic Chemistry
- Materials Chemistry