Comb-shaped poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) polymers with quaternary ammonium (QA) groups have been synthesized organizing into well-defined micro-morphology for efficient anion (hydroxide) transport. These molecular comb structures show a dramatic enhancement in conductivity and water resistance compared with non-comb-shaped PPOs.

Polymers with hydrogen-bonding groups in the melt state often combine the ability to form specific supramolecular bonds with a tendency for unspecific aggregation and microphase separation. Using a combination of small-angle X-ray scattering and shear spectroscopy, we present a study of structure formation and rheological properties of such a case, an exemplary series of telechelic polyisobutylenes, functionalized with hydrogen-bonding end groups. Unspecific interaction between hydrogen-bonding groups leads to the formation of micelles. For monofunctional samples, we observe ordering at lower temperatures, induced by a temperature dependent concentration of the micelles. The rheological properties of these systems can be mapped to the behavior of a concentrated colloidal fluid or solid. For bifunctional polymers with complementary hydrogen-bonding groups, interaction between micellar aggregates leads to network formation and solidlike properties at lower temperatures induced by gelation without ordering. Only in this case the supramolecular bonds directly determine the rheological properties.

Reversible polymeric networks can show self-healing properties due to their ability to reassemble after application of stress and fracture, but typically the relation between equilibrium molecular dynamics and self-healing kinetics has been difficult to disentangle. Here we present a well-characterized, self-assembled bulk network based on supramolecular assemblies, that allows a clear distinction between chain dynamics and network relaxation. Small angle x-ray scattering and rheological measurements provide evidence for a structurally well-defined, dense network of interconnected aggregates giving mechanical strength to the material. Different from a covalent network, the dynamic character of the supramolecular bonds enables macroscopic flow on a longer time scale and the establishment of an equilibrium structure. A combination of linear and nonlinear rheological measurements clearly identifies the terminal relaxation process as being responsible for the process of self-healing.

We investigated a series of telechelic polyisobutylenes, previously shown to exhibit self-healing, by means of small-angle X-ray scattering and rheology. All samples form a dense, dynamic network of interconnected micelles resulting from aggregation of the functional groups and leading to viscoelastic behavior. The dynamic character of this network manifests itself in the appearance of terminal flow at long time scales. While the elastic properties are distinctly molecular weight dependent, the terminal relaxation time is controlled by the functional end groups. The yielding properties under large deformation during startup shear experiments can be understood by a model of stress activation of the dynamic bonds. Stress relaxation experiments help to separate the nonlinear response into two contributions: a fast collapse of the network and a slow relaxation, happening on the time scale of the terminal relaxation. The latter is also known to control self-healing of the collapsed structure.

A combination of extensional rheological and in situ synchrotron radiation small-angle X-ray scattering (SR-SAXS) measurements was introduced to investigate critical strain ε* for shish formation and validate whether coil-stretch transition or stretched-network is responsible for shish-kebab formation in high density polyethylene melt. With strain rates ε · larger than a specific value, the critical strain ε* required to induce shish formation turns out to be a constant of about 1.57, which ensure full extension of chain segments with critical entanglement molecular weight locked between two adjacent entanglement points. The results clearly demonstrate that the formation of shish-kebab in polymer melt stems from stretched network instead of coil-stretch transition.