Supramolecular association of acid terminated polydimethylsiloxanes

Thermodynamic description of bis-urea self-assembly: competition between two supramolecular polymers

Supramolecular polymers are chains of small molecules held together through reversible noncovalent interactions. In general, a given monomer self-assembles into a single type of supramolecular polymer. However, in a few cases, two different self-assembled structures can coexist; this yields interesting responsive systems. To improve the understanding of these systems, we report an association model describing the self-assembly of a supramolecular polymer into two competing forms. The parameters controlling the system were measured by high sensitivity differential scanning calorimetry and isothermal titration calorimetry in the case of a hydrogen-bonded bis-urea supramolecular polymer solution in toluene. The model enables us to compute the proportion and length of all components in the system at any temperature and concentration. The results of these calculations are in agreement with the experimental phase diagram and with independent viscosity measurements.

Dynamical properties of semidilute solutions of hydrogen-bonded supramolecular polymers

The dynamical properties of semidilute solutions of supramolecular polymers formed from molecular recognition directed association between monomers bearing complementary hydrogen bonding groups were investigated by rheological and dynamic light scattering experiments. The steady-state flow curves showed a shear banding type instability, namely the occurrence of a stress plateau sigma(p) above a critical shear rate .gamma(c) . The values of sigma(p)and .gamma(c) were found to be of the same order of magnitude as those of the elastic plateau modulus and the inverse stress relaxation time, respectively. The above features are in agreement with the theoretical predictions based on the reptation model. Dynamic light scattering experiments showed the presence in the autocorrelation function of the concentration fluctuations of a slow viscoelastic relaxation process that is likely to be of Rouse type.