LIVING POLYMERS IN ORGANIC-SOLVENTS - STRESS-RELAXATION IN BICOPPER TETRACARBOXYLATE TERT-BUTYL CYCLOHEXANE SOLUTIONS

Viscoelastic solutions of a bicopper tetracarboxylate complex in tert- butylcyclohexane have been studied by dynamic rheology in a wide range of concentrations (0.5-15.5% volume fraction). The zero shear viscosi ty, the elastic modulus, the terminal stress relaxation time and the h eight of the high-frequency dip, in a Cole-Cole representation of the complex elastic modulus, follow scaling laws. The related exponents ar e discussed in the context of the physics of ''living polymers'': a te rm used to describe worm-like species undergoing scission/recombinatio n reactions competing mainly with the reptation motions of the chains. The current system, made up of molecular threads (17.5 angstrom diame ter) of Cu2(O2C-CH(C2H5) C4H9)4 in the apolar solvent, is representati ve of a ''living polymer'' where, instead of mechanisms involving tran sient star polymeric crosslinks, a reversible scission mechanism preva ils. The dynamics in the high-frequency range evolves from a regime wh ere reptation is the dominant relaxation mechanism to a cross-over reg ime where ''breathing'' fluctuations and Rouse motions become importan t. Large modifications of the stress relaxation function occur for mor e concentrated systems. The binary system is the first example of a '' living polymer'' in an organic solvent and exhibits elastic moduli (G almost-equal-to ca. 120 Pa at phi = 1 %) which are at least 20 times l arger than those found for the aqueous ''living polymer'' systems.