Improvement and tuning of the performance of light-healable polymers by variation of the monomer content†
Photo-healable crosslinked epoxy polymers were produced by combining two commercially available epoxy monomers with a newly sythesised diamine crosslinker (APCD). The crosslinker contains a photocleavable unit in the centre which allows decrosslinking and recrosslinking of the crosslinked polymer network under different UV wavelengths. This behaviour was shown to give rise to the ability to heal a surface scratch after irradiation with 254 nm UV light, and subsequent 365 nm irradiation leads to almost complete recovery of the original coating properties. Three epoxy monomer systems were used to demonstrate the ability to tune the polymer's properties without compromising the healing performance: two single epoxy polymers (APCD/PDE and APCD/BDE) were prepared and a third polymer was prepared by mixing the two monomers in a 50 : 50 mixture (APCD/BP50). It was found that the rigid polymer had a poor healing ability compared to the flexible polymer but the 50 : 50 mixture polymer had the coating performance of the rigid polymer and the healing ability of the flexible polymer.