Substituted polynorbornene membranes: a modular template for targeted gas separations

This perspective focuses on substituted polynorbornenes as a promising modular platform to access advanced gas separation membranes, and highlights their synthetic versatility and robust performance.

Synthesis of polydicyclopentadiene using the Cp2TiCl2/Et2AlCl catalytic system and thin-layer oxidation of the polymer in air

The polymerization process of dicyclopentadiene using a multicomponent catalytic system based on bis(cyclopentadienyl)titanium dichloride and diethylaluminum chloride was studied. It was demonstrated that the application of an excess of the aluminum component leads to the formation of stable charged complexes of blue discoloration, which initiate cationic polymerization of dicyclopentadiene. Unstabilized thin layers of obtained polydicyclopentadiene undergo oxidation and structuring under atmospheric oxygen. Oxidation of polydicyclopentadiene films in air occurs slowly during several weeks and can be determined by the increase of carbonyl and hydroxyl adsorption bands in infrared spectra. Along with oxidation, cross-linking processes occur in polymers, which lead to a change in physical parameters of the layers, and more precisely to a decrease in the permeability of atmospheric oxygen through the layers. Consequently, this leads to the transition of the oxidation from a kinetic mode into a diffusive mode. Such structural changes do not occur in a polymer that was stabilized by adding an antioxidant.

Mechanics and nanovoid nucleation dynamics: effects of polar functionality in glassy polymer networks

We use molecular simulations and experiments to rationalize the properties of a class of networks based on dicyclopentadiene (DCPD), a polymer with excellent fracture toughness and a high glass transition temperature (Tg), copolymerized with 5-norbornene-2-methanol (NBOH). DCPD is a highly non-polar hydrocarbon, while NBOH contains a hydroxy group, introducing polar functionality and hydrogen bonds (H-bonds). NBOH thus represents a possible route to improve the chemical compatibility of DCPD-based networks with less-hydrophobic materials. We systematically vary the NBOH content (polar chemistry) in DCPD networks, while keeping other network parameters nearly constant, including the molecular weight between cross-links, chain rigidity, and Tg. Using molecular dynamics (MD) simulations, we quantify the thermovolumetric and mechanical properties, including Tg, cohesive energy density, stiffness, and yield strength. We compare these results with experiments on networks of similar composition, finding good agreement. The relation between these properties and polar chemistry are studied by examining a secondary network of physical cross-links, formed by hydrogen bonds between NBOH units. Further, we examine nanovoid formation, an energy dissipation mechanism hypothesized to contribute to the toughness of pDCPD. Using metadynamics to accelerate sampling, we quantify the nanovoid nucleation rate under hydrostatic tension, similar to the stress state in the plastic zone preceding a crack tip. Small additions of NBOH have minimal effect, but the rate drops steeply with larger amounts. Several properties are mapped at nanometer scales, including stiffness and mobility, and associated with void nucleation. Estimates of the length- and time-scale of the plastic zone near a crack tip are used in discussing nanovoid formation as a plausible toughening mechanism in these materials. Overall, the results suggest that pDCPD tolerates the addition of some polar chemistry without degrading its excellent mechanical properties.

Advances in self-healing materials based on vascular networks with mechanical self-repair characteristics

Here, we review the state-of-the-art in the field of engineered self-healing materials. These materials mimic the functionalities of various natural materials found in the human body (e.g., the healing of skin and bones by the vascular system). The fabrication methods used to produce these "vascular-system-like" engineered self-healing materials, such as electrospinning (including co-electrospinning and emulsion spinning) and solution blowing (including coaxial solution blowing and emulsion blowing) are discussed in detail. Further, a few other approaches involving the use of hollow fibers are also described. In addition, various currently used healing materials/agents, such as dicyclopentadiene and Grubbs' catalyst, poly(dimethyl siloxane), and bisphenol-A-based epoxy, are described. We also review the characterization methods employed to verify the physical and chemical aspects of self-healing, that is, the methods used to confirm that the healing agent has been released and that it has resulted in healing, as well as the morphological changes induced in the damaged material by the healing agent. These characterization methods include different visualization and spectroscopy techniques and thermal analysis methods. Special attention is paid to the characterization of the mechanical consequences of self-healing. The effects of self-healing on the mechanical properties such as stiffness and adhesion of the damaged material are evaluated using the tensile test, double cantilever beam test, plane strip test, bending test, and adhesion test (e.g., blister test). Finally, the future direction of the development of these systems is discussed.

Thermally Crosslinked Functionalized Polydicyclopentadiene with a High T g and Tunable Surface Energy

Polydicyclopentadiene (PDCPD) is a tough, heavily crosslinked thermoset polymer that has high heat, chemical, and impact resistance coupled with a low density. Current limitations to the broader industrial application of PDCPD include its low surface energy and lack of chemical tunability. Here, we report the first example of a polymer derived from a carboxyl-functionalized dicyclopentadiene monomer and its subsequent thermal crosslinking. The resulting material has the highest glass-transition temperature reported for a polydicyclopentadiene and allows for the facile manipulation of the surface chemistry through alteration of the embedded functional group. We also report the first observation by differential scanning calorimetry of the crosslinking step as a discreet thermal event.

Cross-linked ROMP polymers based on odourless dicyclopentadiene derivatives

Hydroxydicyclopentadiene (DCPD-OH) and some ester and ether derivatives were synthesized and used for the first time as ring-opening metathesis polymerization (ROMP) monomers to create cross-linked thermoset polymers with Ru-catalysts.

Cure kinetics and physical properties of poly(dicyclopentadiene/5-ethylidene-2-norbornene) initiated by different Grubbs' catalysts

Cure kinetics ofendo-dicyclopentadiene (DCPD)/5-ethylidene-2-norbornene (ENB) blends with 1^stand 2^ndgeneration Grubbs' catalysts were characterized using dynamic differential scanning calorimetry.

Inverse electron demand Diels-Alder (iEDDA) functionalisation of macroporous poly(dicyclopentadiene) foams

Inverse electron demand Diels-Alder reactions performed on the double bonds in open cellular macroporous poly(dicyclopentadiene) monoliths yield a high degree of functionalisation (up to 2 mmol pyridazines per g or 8 mmol N per g) with grafted di(pyridyl)pyridazines in a single step.