Synthesis and properties of cross-linked polymers containing diarylbibenzofuranone by ADMET polymerization

Diarylbibenzofuranone (DABBF) derivatives can be reversibly cleaved to the corresponding arylbenzofuranone (ABF) radicals under mild conditions. We recently reported the synthesis and physicochemical properties of the cross-linked polyurethane containing DABBF unit. The autonomous structural transformation and the macroscopic self-healing of separated gel pieces under air at room temperature without any stimuli were accomplished by a dynamic covalent approach. Since the self-healing property was derived from DABBF units, one can expect the self-healing of DABBF-containing cross-linked polymers with various structures. We here report the acyclic diene metathesis (ADMET) polymerization of multifunctional olefin monomers containing DABBF unit. This is because a low-polarity olefin polymer can be obtained by ADMET polymerization. The DABBF-diolefin monomer was first polymerized at room temperature in the presence of Grubbs catalyst (2nd generation) in CH2Cl2. However, the yield of the obtained polymer was low (29%). Under this condition, it is considered that the ethylene molecules produced during polymerization can not be removed. The polymerization was also performed at 40 °C to give polymers in good yield (83%). Furthermore, cross-linked polymers were synthesized by ADMET polymerization of DABBF-tetraolefin monomer and copolymerization of DABBF-bifunctional olefin monomer and triolefin monomer. All cross-linked polymers were obtained in good yields. These polymers showed high swelling properties in organic solvents with relatively low polarity

Self-healing and mechanochromism of diarylbibenzofuranone-based dynamic covalent polymers

Covalent bonds with the ability to reach an equilibrium state between combination and dissociation under certain conditions have been studied, and systematic method for controlling the structures of compounds and polymers based on these reversible covalent bonds has been spotlighted as dynamic covalent chemistry. In the present study, diarylbibenzofuranone (DABBF)-based dynamic covalent polymers were designed with two notable functionalities, self-healing of polymer gels cross-linked by DABBF and mechanochromism of DABBF-containing linear polyurethanes. Cross-linked polymers with exchangeable dynamic covalent bond at room temperature were synthesized by polyaddition of DABBF-tetraol and tolylene diisocyanate terminated polypropylene glycol. The self-healing property of the DABBF-containing cross-linked polymer gel was investigated under air at room temperature. The gel samples were prepared and cut with a razor blade to expose fresh surfaces. The fresh surfaces were brought together immediately in the absence of external force. The in-contact samples were kept at room temperature under air. After 24 h, self-healing of the contacted samples could be observed and the scars had almost disappeared. Even after manually stretching the sample, no destruction occurred. Tensile tests were also performed to quantitatively evaluate self-healing properties. A recovery of 98 % of the original elongation at breaking was possible over periods of 24 h. Stimuli-responsive polymers which show color change by mechanical stress were also synthesized and their mechanochromic behavior was investigated. Since the central C-C bonds in DABBF have lower bond dissociation energy, DABBF can reversibly cleave to the corresponding radicals with blue color. We employed DABBF as a mechanochromic unit. DABBF-containing polyurethane films were prepared and their elongation-induced color change was observed