Supramolecular thermoplastic with 0.5 Pa·s melt viscosity.

Design of materials with polymer-like properties at service temperature but able to flow like simple liquids when heated remains one of the important challenges of supramolecular chemistry. Combining these antagonistic properties is highly desirable to provide durability, processability, and recyclability of materials. Here, we explore a new strategy based on polycondensation reactions to design supramolecular polymer materials with stress at break above 10 MPa and melt viscosity lower than 1 Pa·s. We report the synthesis and rheological and mechanical properties (uniaxial tensile tests) of supramolecular polymers based on a multiblock polyamide architecture. The flexibility of polycondensation reactions made it possible to control the molecular size distribution, the strength of hydrogen bonds, and the crystallization of middle and end groups and to achieve targeted properties.

Metal-catalyzed transesterification for healing and assembling of thermosets.

Catalytic control of bond exchange reactions enables healing of cross-linked polymer materials under a wide range of conditions. The healing capability at high temperatures is demonstrated for epoxy-acid and epoxy-anhydride thermoset networks in the presence of transesterification catalysts. At lower temperatures, the exchange reactions are very sluggish, and the materials have properties of classical epoxy thermosets. Studies of model molecules confirmed that the healing kinetics is controlled by the transesterification reaction rate. The possibility of varying the catalyst concentration brings control and flexibility of welding and assembling of epoxy thermosets that do not exist for thermoplastics.

Catalytic Control of the Vitrimer Glass Transition.

Vitrimers, strong organic glass formers, are covalent networks that are able to change their topology through thermoactivated bond exchange reactions. At high temperatures, vitrimers can flow and behave like viscoelastic liquids. At low temperatures, exchange reactions are very long and vitrimers behave like classical thermosets. The transition from the liquid to the solid is reversible and is, in fact, a glass transition. By changing the content and nature of the catalyst, we can tune the transesterification reaction rate and show that the vitrimer glass transition temperature and the broadness of the transition can be controlled at will in epoxy-based vitrimers. This opens new possibilities in practical applications of thermosets such as healing or convenient processability in a wide temperature range.

Silica-like malleable materials from permanent organic networks.

Permanently cross-linked materials have outstanding mechanical properties and solvent resistance, but they cannot be processed and reshaped once synthesized. Non-cross-linked polymers and those with reversible cross-links are processable, but they are soluble. We designed epoxy networks that can rearrange their topology by exchange reactions without depolymerization and showed that they are insoluble and processable. Unlike organic compounds and polymers whose viscosity varies abruptly near the glass transition, these networks show Arrhenius-like gradual viscosity variations like those of vitreous silica. Like silica, the materials can be wrought and welded to make complex objects by local heating without the use of molds. The concept of a glass made by reversible topology freezing in epoxy networks can be readily scaled up for applications and generalized to other chemistries.

Tunable and reversible aggregation of poly(ethylene oxide-st-propylene oxide) grafted gold nanoparticles.

Two amino-terminated amphiphilic copolymers, M600 and M1000, with different ethylene oxide to propylene oxide EO/PO ratios, 1/9 and 19/3, respectively, were coupled by thioctic acid, which allows an excellent affinity with gold surface. Then, amphiphilic thermally responsive gold nanoparticles (AuNPs) were prepared either by ligands exchange on precursor gold nanoparticles or by direct reduction of gold source in presence of stabilizing copolymers. The as-obtained AuNPs are monodisperse with a size varying from 2 to 17 nm depending on the synthesis used. The main parameters controlling the AuNPs assemblies were identified: the ethylene oxide to propylene oxide ratio in the polymer corona, the ionic strength of the solution, and the curvature of AuNPs. An interesting result is the possibility to tune the aggregation temperature from 8 to 15 degrees C of AuNPs coated by the same polymer only by changing the curvature of the AuNPs from 17 to 2 nm. This temperature change versus the curvature of the nanoparticle is ascribed to the decrease in hydration volume per hydrophilic group in the corona due to the change of the polymer chain conformation with changing the particle size. Moreover, one unique aggregation temperature between 12 and 60 degrees C can be also obtained by mixing copolymers with different EO/PO ratios. Then, the corona, constituted by a mixture of polymers, behaves as a corona composed by an average statistic copolymer with the intermediate composition.