Effect of Varying Poly(dimethylsiloxane) Chain Length and Content, and the Infusion of Free Silicone Oil on the Antismudge Properties of NP-GLIDE Polyurethane Coatings

Abstract

NP-GLIDE polyurethane (PU) coatings are prepared by curing a commercial polyol, a hexamethylene diisocyanate trimer (HDIT), and P1-g-PDMS, a graft copolymer consisting of a polyol backbone and grafted poly(dimethylsiloxane) (PDMS) side chains. These coatings are termed NP-GLIDE coatings because most test liquids with surface tension values higher than ~22 mN/m have no problem to glide cleanly off them and the coatings contain on their surfaces and within the PU matrix nanopools of a grafted liquid ingredient (PDMS) for dewetting enablement. To optimize the dewetting performance of the NP-GLIDE coatings, the effect of varying the length of the PDMS chains in the P1-g-PDMS samples was investigated. P1-g-PDMS polymers with PDMS molecular weight of 1.00 × 103, 5.0 × 103, and 10.0 × 103 g mol-1 were synthesized and cast together with a commercial polyol and HDIT as transparent antismudge coatings. Studies showed that when the PDMS molecular weight was 10.0 × 103 g mol-1, the dewetting ability of the coating was lower than that prepared from P1-g-PDMS with PDMS molecular weight at 5.0 × 103 g mol-1. This result should be due to the higher viscosity of the higher molecular weight PDMS and therefore lower mobility of the surface PDMS chains. When the PDMS molecular weight was 1.00 × 103 g mol-1, the resultant coating did not perform well either, likely due to the fact that the surface PDMS layer was not thick enough to fully cover the surface. Using a PDMS molecular weight in between (MW = 5.0 × 103 g mol-1), proved to provide the best compromise between surface coverage and viscosity and resulted in the best dewetting performance. The effects of varying PDMS content and incorporating free silicone oil into the coatings were also examined. Coatings with 1.00 to 6.0 wt. % PDMS showed good dewetting properties, with higher PDMS content performing slightly better. 1.00 wt. % PDMS was proved to be the lower limit of PDMS content as coatings with 0.50 wt. % PDMS were unable to shrink ink or paint. Infusing the sample with free silicone oil also showed improved contact angles, sliding angles, and contact angle hysteresis especially when water was used as the test liquid.