Researchers from UK investigated self-healing efficiency of coatings, synthesized from polycarbonate polyol with molecular mass of 500 Da and hexamethylene diisocyanate or isophorone diisocyanate, without a chain extender, with aliphatic diol with two to five carbon atoms or with diethylene glycol. Self-healing efficiency of coatings were examined by comparison of haze before damage and at intervals after damage which was made by a steel-wool scratch instrument and then coatings were left to heal at room temperature and at 60 °C. The tests were repeated after 12 weeks in order to investigate ageing of the polymers. UV weathering test was also performed.

It was revealed that up to 100% recovery within 10 min at 60 °C and partial recovery at room temperature were found for optimally designed coatings. The self-healing property was found to be linked to macro-organisation of polymer chains caused by interactions between hard segments and soft segments of the polyurethane moiety, leading to phase-mixing, promoted by bulky, non-symmetrical isophorone diisocyanate, or phase-separation, promoted by linear, symmetrical hexamethylene diisocyanate. Moreover, it was also found that coatings are resistant to UV weathering.

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This article is published in Progress in Organic Coatings, Volume 122, September 2018, Pages 1-9.