Halato-telechelic polymers. 8. Dependence of the viscoelastic behavior on the prepolymer molecular weight

Using Coupling Motion of Connecting Ions in Designing Telechelic Ionomers

Conventional telechelic ionomers have one ion fixed at each end, enabling the chains to form a physical network. Here we report a type of telechelic ionomers with a distribution of the number of ions at the chain ends, which endows them with very rich rheological properties. We synthesized the ionomer samples via a two-step polymerization. Namely, we synthesized a precursor chain first and then polymerized a few ion-containing monomers at its two ends. An average number of ion-containing monomers per chain end, m, varies from 0 to 3.0. Linear viscoelasticity of these samples can be well explained through considering the Poisson distribution of m, and the hierarchical relaxation of the chains ends according to the number of connecting ions that exhibit the coupling motion.

What dielectric spectroscopy can tell us about supramolecular networks⋆

Polymers which can form supramolecular networks are a promising class of materials to provide highly sought-after properties such as self-healing, enhanced mechanical strength, super-stretchability as well as easy recyclability. However, due to the vast range of possible chemical structures it is very demanding to optimize these materials for the desired performance. Consequently, a detailed understanding of the molecular processes that govern the macroscopic properties is paramount to their technological application. Here we discuss some telechelic model systems with hydrogen-bonding end groups and how dielectric spectroscopy in combination with linear oscillatory shear rheology helped to understand the association mechanism on a molecular scale, and verify the model of bond-lifetime renormalization. Furthermore, we analyze a limitation of these H-bonding polymers, namely that there is a trade-off between high plateau modulus and long terminal relaxation time --both cannot be maximized at the same time. Finally, we show how more complex end groups phase separate from the main chain melt and thus lead to a more sophisticated rheological behavior which can overcome that limitation.

Physical organic chemistry of supramolecular polymers

Unlike the case of traditional covalent polymers, the entanglements that determine properties of supramolecular polymers are defined by very specific, intermolecular interactions. Recent work using modular molecular platforms to probe the mechanisms underlying mechanical response of supramolecular polymers is reviewed. The contributions of supramolecular kinetics, thermodynamics, and conformational flexibility to supramolecular polymer properties in solutions of discrete polymers, in networks, and at interfaces, are described. Molecule-to-material relationships are established through methods reminiscent of classic physical organic chemistry.