Highly Transparent and Colorless Self‐Healing Polyacrylate Coatings Based on Diels–Alder Chemistry

Abstract

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.,

Self-Healing in Mobility-Restricted Conditions Maintaining Mechanical Robustness: Furan–Maleimide Diels–Alder Cycloadditions in Polymer Networks for Ambient Applications

“…The majority of self-healing studies on reversible covalent polymer networks focusses on materials in the elastomeric state. This means that the sealing and healing stages are performed at temperatures (T app ) higher than the material's glass transition temperature (T g ), at which the polymer network exhibits sufficient segmental mobility (T app > T g ) [34,36,[43][44][45].…”

Improvement of Mechanical and Self-Healing Properties for Polymethacrylate Derivatives Containing Maleimide Modified Graphene Oxide

“…The Diels-Alder reaction can be applied to various polymers. Most of all, there are many studies that apply the Diels-Alder reaction to acrylate polymer, which is widely 2 of 14 used in coating materials [22][23][24][25][26][27][28][29]. In particular, the application of graphene or modified graphene oxide to self-healing polymers not only improves their mechanical properties, but also their healing efficiency [30][31][32][33][34][35][36][37].…”

Progress and challenges in self-healing composite materials

“…After that lowering, the temperature causes the bonds to reforms and heal the cracks [47]. Fortunato et al obtained reversible networks by reacting a series of linear copolymers of furfuryl methacrylate with aliphatic bismaleimides through DA reaction between furan and maleimide moieties and developed highly transparent and colorless self-healing polyacrylate coatings [48].…”