A self-healing polymer network based on reversible covalent bonding

摘要

A self-healing polymer network for potential coating applications was designed based on the concept of the reversible Diels-Alder (DA) reaction between a furan functionalized compound and a bismaleimide. The network allows local mobility in a temperature window from ca. 80 ℃ to 120 ℃ by shifting the DA equilibrium towards the initial building blocks. Changing the spacer length in the furan functionalized compound leads to tailor-made properties. Elastomeric model systems were chosen to evaluate the kinetic parameters by Fourier transform infrared spectroscopy. For the DA reaction a pre-exponential factor ln(A_(DA) in kg mol~(-1) s~(-1)) equal to 13.1 ±0.8 and an activation energy (E_(DA)) of 55.7 ±2.3 kJ mol~(-1) are found. For the retro-DA reaction, ln(A_(rDA)) and E_(rDA) are 25.8 ±1.8 s~(-1) and 94.2 ± 4.8 kJ mol~(-1), respectively. The enthalpy and entropy of reaction are calculated as -38.6 kJ mol~(-1) and -105.3 J mol~(-1) K~(-1). The kinetic results are validated by micro-calorimetry. Non-isothermal dynamic rheometry provides the gel-point temperature of the reversible network. The sealing capacity is evaluated by atomic force microscopy for micro-meter sized defects. Repeatability of the non-autonomous healing is checked by micro-calorimetry, ruling out side-reactions below 120℃.