UV Curing Behavior of Five Heteroleptic POSS Bearing Methacrylate and Glycidyl Groups and Evaluation of Their Potential for Hard Yet Flexible Coatings

Octakis(3-methacryloxypropyl) silsesquioxane (MPOSS) photocured using a free-radical initiator under N-2 has a high hardness H of 0.99 +/- 0.05 GPa but has poor bendability. Octakis(3-glycidyloxypropyl) silsesquioxanes (GPOSS) photocured in air using a cationic initiator is more flexible than the cured MPOSS coating but has a lower H value of 0.65 +/- 0.02 GPa. In this study, a family of heteroleptic POSSs (G(m)M(n)POSS) bearing 2, 4, or 6 glycidyl (G) groups and 6, 4, or 2 methacrylate (M) groups are photocured in N-2, in air, in air then N-2 (air/N-2), and in N-2/air. The hardest coating is obtained from a given precursor G(m)M(n)POSS when it is cured in N-2/air. The G(2)M(6)POSS coating offers the best balance between H and bendability. At a thickness of 50 mu m, this coating has an H value of 0.95 +/- 0.07 GPa, a pencil hardness rating of >9H, and a critical bending radius of <1 mm for inward bending on the inner surface of a poly(ethylene terephthalate) substrate film. At a thickness of 10 mu m, the G(2)M(6)POSS coating has a critical outward bending radius of 1.5 mm. This study provides experimental guidelines for the proper photocuring of G(m)M(n)POSS and reveals that G(2)M(6)POSS is the best candidate for hard yet flexible coatings, which may be used to protect the touchscreens of foldable smartphones among other applications.

Automated summary

In this study, a series of heteroleptic POSSs were photocured under different conditions, and it was found that the G(2)M(6)POSS coating cured in N-2/air obtained the hardest coating. This coating has high hardness and good flexibility, making it suitable for protecting the touchscreens of foldable smartphones among other applications.