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
Prolonged durability in outdoor environment and ease of application are highly required features for self-healing coatings. To this end, a novel transparent and self-healing nanocomposite for optical applications, based on Diels-Alder (DA) chemistry is developed in this work. First, a novel, highly soluble, bismaleimide enabled a simple coating fabrication by coupling with furan-functionalized polyacrylates in industrially relevant solvents. The resulting crosslinked coatings exhibited high transparency and complete absence of color, as assessed by UV-vis spectroscopy. Their thermal behavior and the conditions required by the healing process were significantly affected by the degree of furan/maleimide functionality of the system. Secondly, the addition of a small amount of a commercial antioxidant stabilized the optical properties against photo-oxidative weathering, both on clear and titania-pigmented coatings, as determined by colorimetric analysis. Finally, dispersion of silica nanoparticles in the DA-based matrix allowed to enhance the surface hardness of the coatings, while retaining the self-healing ability.
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.
the development of approaches based on disulfide bond exchange, [3] alkoxyamine dissociation, [4] thiol-Michael reaction, [5] Alder-ene addition, [6] and bulky urea bonds, [7] the most widely reported systems are based on the well-established Diels-Alder (DA) cycloaddition. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] DA is a click-type addition reaction between a dienophile and a diene, typically a maleimide and a furan. The design of a polymer network where crosslinks are constituted by DA adducts would result in the ability to cleave the crosslinks at mildto-high temperature through a retro Diels-Alder process (r-DA), while enabling their reformation upon cooling through the direct DA reaction. Therefore, the r-DA/ DA sequence can be exploited to repair cracks or to remold the crosslinked material. [24] The concept, firstly described in a patent [25] and then in the milestone work of Wudl [26] has been exploited for the dynamic crosslinking of different polymer matrices like epoxies, [27,28] elastomers, [29,30] polyesters, [31,32] and polyketones. [33,34] A straightforward strategy to design DA crosslinked acrylates is based on the combination of linear copolymers of furfuryl methacrylates (FMAs) with difunctional maleimide linkers. [8][9][10]12,16,20] The reported systems are typically characterized by high healing efficiency. However, they lack in transparency and usually exhibit a yellow-to-orange color, predominantly due to the use of aromatic bismaleimide linkers. This feature factually forbids the utilization of DA-based acrylates for optical applications, where high levels of transmittance in the visible wavelength range are inevitably required.To bridge this gap, a straightforward strategy to prepare colorless and transparent thermoresponsive acrylates based on the DA chemistry is proposed in this work. Furan functional polyacrylates were synthetized via free radical polymerization of FMA with methacrylates bearing different aliphatic groups. Two aliphatic bismaleimides, with different chain length, were synthesized starting from the respective diamines. The obtained linear copolymers containing furan moieties were combined with the bismaleimides in solvent, and colorless, high-transmittance, crosslinked coatings were obtained. The thermal reversibility of the DA-coatings was assessed by means of differential scanning calorimetry (DSC) and solubility experiments. After assessing the self-healing ability of the acrylicbased polymeric materials, the effect of network structure (i.e.,
This work focuses on the design of an engineered thermoplastic polymer containing pyrrole units in the main chain and hydroxyl pendant groups (A-PPy-OH), which help in achieving nanocomposites containing well-distributed, exfoliated and undamaged MWCNTs. The thermal annealing at 100 °C of the pristine nanocomposite promotes the redistribution of the nanotubes in terms of a percolative network, thus converting the insulating material in a conducting soft matrix (60 μΩ m). This network remains unaltered after cooling to r.t. and successive heating cycles up to 100 °C thanks to the effective stabilization of MWCNTs provided by the functional polymer matrix. Notably, the resistivity-temperature profile is very reproducible and with a negative temperature coefficient of -0.002 K-1, which suggests the potential application of the composite as a temperature sensor. Overall, the industrial scale by which A-PPy-OH can be produced offers a straightforward alternative for the scale-up production of suitable polymers to generate multifunctional nanocomposites
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