A self-healing polymer network based on reversible covalent bonding

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 degrees C to 120 degrees C 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 In(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, In(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 degrees C. (C) 2012 Elsevier Ltd. All rights reserved.