Quadruple hydrogen-bonded supramolecular polymers : complementarity versus self-complementarity

Abstract onl

Mechanical activation of a latent olefin metathesis catalyst and persistence of its active species in ROMP

Preparation, substrate scope, and activity of a previously reported mechanically activated metathesis catalyst were investigated. Scission of the catalyst under ultrasound irradiation was followed by GPC, which showed a first-order scission rate constant of 0.011 min(-1). The resulting active species was shown to have catalytic reactivity in ring closing metathesis (RCM) of various (un)hindered substrates. Further investigations of the active species showed that it was not influenced by radicals formed during ultrasound and that the most effective method to increase its lifetime was an increase in the substrate concentration. In ring-opening metathesis polymerization (ROMP), the lifetime of the active species was shown to be several hours, in contrast to the short lifetimes found in RCM. ROMP experiments also showed that all of the latent precatalyst broken leads to active catalyst species

Dioxetanes as mechanoluminescent probes in thermoplastic elastomers

Mechanoluminescent 1,2-dioxetane units, which emit light upon scission of the strained 4-membered ring, were incorporated into the main chain of segmented copolymers with poly(tetramethylene oxide) soft segments and various hard segments. Test samples of the polymers emitted light upon applying strain. Polymers with hydrogen bonding urethane or amide groups in the hard segments showed stronger luminescence than polyester segmented copolymers of similar molecular weight. Increasing strain rate led to stronger luminescence. The positive effect of molecular weight on emission intensity in polyurethanes was interpreted in terms of decreased chain slippage when multiple hard segments anchor the polymer chain in different hard blocks. The results demonstrate that even chains with more than 50 hard segments slippage can be further reduced by increasing the degree of polymerization

Pi-extended anthracenes as sensitive probes for mechanical stress

Smart molecular systems having the ability to report on mechanical strain or failure in polymers via alteration of their optical properties are of great interest in materials science. However, only limited attention has been devoted to targeted chromophore engineering to fine-tune their physicochemical properties. Here, we describe the synthesis of π-extended anthracenes that can be released from their respective maleimide Diels–Alder adducts through the application of mechanical stress in solution and in the solid state. We demonstrate the improvement of fluorescence quantum yield as well as the tuning of excitation and emission wavelengths while retaining their excellent mechanochemical properties laying the foundation for a new series of mechanophores whose spectral characteristics can be modularly adjusted

Easily accessible thermotropic hydrogen-bonded columnar discotic liquid crystals from fatty Acid– Tris-Benzoimidazolyl Benzene complexes

\u3cp\u3eWe report the formation of easily accessible hydrogen-bonded columnar discotic liquid crystals (LCs) based on tris-benzoimidazolyl benzene (TBIB) and commercially available fatty acids. By increasing the length of the fatty acid, the temperature range of liquid crystallinity was tuned. Introducing double bonds in octadecanoic acid lowered the crystallization temperature and increased the temperature range of the mesophase. Surprisingly, dimerized linoleic acid also forms an LC phase. When using branched aliphatic acids with the branching point close to the acid moiety, the mesophase was lost, whereas phosphonic acid or benzenesulfonic acid derivatives did have a mesophase, showing that the generality of this approach extends beyond carboxylic acids as the hydrogen-bond donor. Furthermore, a polymerizable LC phase was obtained from mixtures of TBIB with a methacrylate-bearing fatty acid, providing an approach for the fabrication of nanoporous polymer films if the methacrylate groups are polymerized. Finally, the higher solubility of methyl-TBIB was used to suppress phase separation in stoichiometric mixtures of the template molecule with fatty acids.\u3c/p\u3

Unexpected entropy-driven ring-opening polymerization in a reversible supramolecular system

Communication - No abstract

Effects of surfactant and urea on dynamics and viscoelastic properties of hydrophobically assembled supramolecular hydrogel

\u3cp\u3ePhysically associated hydrogels based on strong hydrophobic interactions often have attractive mechanical properties that combine processability with elasticity. However, there is a need to study such interactions and understand their relation to the macroscopic hydrogel properties. Therefore, we use the surfactant sodium dodecyl sulfate (SDS) and urea as reagents that disrupt hydrophobic interactions. The model hydrogel is based on a segmented copolymer between poly(ethylene glycol) (PEG) and hydrophobic dimer fatty acid (DFA). We show that both agents influence viscoelastic properties, dynamics, and relaxation processes of the model hydrogel. In particular, the relaxation time is significantly reduced by urea, as compared to SDS, whereas the surfactant causes a decrease of the modulus of the hydrogel more efficiently. The reversibility of the effects of SDS and urea can be exploited, for instance, by using an injectable sol that solidifies when the SDS or urea diffuses out of the sample. Surfactant-induced processability may be advantageous in future applications of hydrophobically assembled physical hydrogels.\u3c/p\u3

Pore size dependent cation adsorption in a nanoporous polymer film derived from a plastic columnar phase

\u3cp\u3eSelf-supporting polymer thin films were obtained by the polymerization of an AB\u3csub\u3e3\u3c/sub\u3e-type hydrogen-bonded complex in the plastic columnar phase. Porous polymers with pore diameters of ≈1.1 and ≈1.6 nm lined with either -COOH or -COONa groups were fabricated from the polymer thin films. Both the pore size and pore collapse influence the adsorption of cations.\u3c/p\u3