A study of the temperature dependent healing capabilities of new polymers based on Diels-Adler cycloaddition

Abstract

Because of its thermal reversibility, the retro-Diels-Alder (RDA) reaction represents an appealing possibility to produce self-healing polymers with well-defined architectures and tunable properties [1]. However, the polymer architecture for which the Diels-Alder (DA) reaction can best be used to contribute to the healing process is still not well-defined. Therefore, new terpolymers containing moieties for the reversible crosslinking by the DA reaction have been synthesized. These linear polymers are based on a methacrylate backbone containing both functionalities in the side chains and represent a one component self-healing system. As a desirable consequence no separate (low molar mass) crosslinker is necessary to obtain the desired self-healing properties. A protected maleimide is used as functional comonomer which can be activated after polymerization. Upon the occurrence of local damage the crosslinked material can be heated to a certain temperature, where the retro-Diels-Alder reaction takes place and the material obtains the necessary local mobility for damage closure. Upon cooling to room temperature, the coupling of the two reactive functional groups takes place and the strength of the material is restored. The synthesis of these terpolymers with maleimide methacrylate (MIMA) and furfuryl methacrylate (FMA) as functional units for the DA cycloadditon and different co-monomers in different ratios were achieved by applying the atom transfer radical polymerization (ATRP). Besides the characterization of the obtained polymers by 1H NMR spectroscopy, SEC, and MALDI-TOF MS, the thermal properties were investigated by TGA and DSC. The damage healing was studied by AFM and SEM. To obtain further details on the healing mechanism at the nanoscale additional temperature dependent FTIR measurements during and after shear flow were made.