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

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journal contribution
posted on 2022-02-10, 22:04 authored by Desiree N. Bender, Sukhendu Hait, Joseph D. Lichtenhan, Guojun Liu
Octakis­(3-methacryloxypropyl) silsesquioxane (MPOSS) photocured using a free-radical initiator under N2 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 (GmMnPOSS) bearing 2, 4, or 6 glycidyl (G) groups and 6, 4, or 2 methacrylate (M) groups are photocured in N2, in air, in air then N2 (air/N2), and in N2/air. The hardest coating is obtained from a given precursor GmMnPOSS when it is cured in N2/air. The G2M6POSS coating offers the best balance between H and bendability. At a thickness of 50 μm, 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 μm, the G2M6POSS coating has a critical outward bending radius of 1.5 mm. This study provides experimental guidelines for the proper photocuring of GmMnPOSS and reveals that G2M6POSS is the best candidate for hard yet flexible coatings, which may be used to protect the touchscreens of foldable smartphones among other applications.