No abstract

The intrinsic self-healing ability of polyketone (PK) chemically modified into furan and/or OH groups containing derivatives is presented. Polymers bearing different ratios of both functional groups were cross-linked via furan/bis-maleimide (Diels-Alder adducts) and hydrogen bonding interactions (aliphatic and aromatic OH groups). The resulting thermosets display tuneable softening points (peak of tan (δ)) from 90 to 137 °C as established by DMTA. It is found that the cross-linked system containing only furan groups shows the highest softening temperature. On the other hand, systems displaying the combination of Diels-Alder adducts and hydrogen bonding (up to 60 mol % of -OH groups) do not show any change in modulus between heating cycles (i.e. factually a quantitative recovery of the mechanical behaviour). It is believed that the novelty of these tuneable thermosets can offer significant advantages over conventional reversible covalent systems. The synergistic reinforcement of both interactions resists multiple heating/healing cycles without any loss of mechanical properties even for thermally healed broken samples

In this work we present a reversible and toughened thermoset system based on the covalent incorporation of a furane functionalized ethylene-propylene rubber (EPM-Fu) into a thermoset furane functionalized polyketone (PK-Fu) via Diels-Alder (DA) reversible cross-linking with bismaleimide (b-MA). FT-IR and DSC analyses proved the reversible interaction between PK-Fu and EPM-Fu with b-Ma via DA and r-DA sequence. Likewise, thermo-mechanical experiments (DMTA) indicated the re-workability of the material with no evident differences in elastic and loss modulus after several heating cycles and recycling procedures. Moreover, a considerable increase in the softening point (tangent d) was also found for the higher toughened system containing 12 wt% of EPM-Fu (neat thermoset T = 137 °C whereas toughened thermoset T = 155 °C). A two-fold increase in IZOD impact strength compared to the neat thermoset (up to 27 J/m) was also recorded by the toughened system. Overall, this approach clearly indicates that fully thermally reversible and toughened thermosets can be realized starting from mixtures of furan functionalized polyketone and EPM rubber, cross-linked via reversible Diels-Alder chemistry.

In this work, we prepared electrically conductive self-healing nanocomposites. The material consists of multi-walled carbon nanotubes (MWCNT) that are dispersed into thermally reversible crosslinked polyketones. The reversible nature is based on both covalent (Diels-Alder) and non-covalent (hydrogen bonding) interactions. The design allowed for us to tune the thermomechanical properties of the system by changing the fractions of filler, and diene-dienophile and hydroxyl groups. The nanocomposites show up to 1 × 104 S/m electrical conductivity, reaching temperatures between 120 and 150 °C under 20–50 V. The self-healing effect, induced by electricity was qualitatively demonstrated as microcracks were repaired. As pointed out by electron microscopy, samples that were already healed by electricity showed a better dispersion of MWCNT within the polymer. These features point toward prolonging the service life of polymer nanocomposites, improving the product performance, making it effectively stronger and more reliable.

Both shape memory and self-healing polymers have received significant attention from the materials science community. The former, for their application as actuators, selfdeployable structures, and medical devices; and the latter, for extending the lifetime of polymeric products. Both effects can be stimulated by heat, which makes resistive heating a practical approach to trigger these effects. Here we show a conductive polyketone polymer and carbon nanotube composite with crosslinks based on the thermo-reversible furan/maleimide Diels−Alder chemistry. This approach resulted in products with efficient electroactive shape memory effect, shape reprogrammability, and self-healing. They exhibit electroactive shape memory behavior with recovery ratios of about 0.9; requiring less than a minute for shape recovery; electroactive self-healing behavior able to repair microcracks and almost fully recover their mechanical properties; requiring a voltage in the order of tens of volts for both shape memory and self-healing effects. To the best of our knowledge, this is the first report of electroactive self-healing shape memory polymer composites that use covalent reversible Diels−Alder linkages, which yield robust solvent-resistant polymer networks without jeopardizing their reprocessability. These responsive polymers may be ideal for soft robotics and actuators. They are also a step toward sustainable materials by allowing an increased lifetime of use and reprocessability.