Transparent and Durable Antismudge Polyurethane Coatings with Octadecyl Chlorosilane-Enhanced Bihydroxypropyl PDMS Polymer Brushes

A liquid-like poly(dimethylsiloxane) (PDMS) brush as an environmentally friendly, low surface energy modifier has a significant effect on improving the antismudge properties of coatings. However, in order to obtain a sufficient length of freely mobile chain segments to meet the liquid repellency, expensive single-terminal functionalized PDMS has to be chosen in the preparation of antismudge coatings. In this work, double-terminal functionalized PDMS was employed to fabricate antismudge polyurethane (PU) coatings with the help of alkyltrichlorosilane (RSiCl3). That is, bihydroxypropyl PDMS (BHPDMS) was terminated with RSiCl3, further grafted onto acrylic polyol chains using its residual Si–Cl bonds, and subsequently cured with an isocyanate trimer. Effects of the molecular weight of BHPDMS (Mn = 1000, 2000, 4300, and 10,000 g/mol) and the type of RSiCl3 (R = methyl, dodecyl, octadecyl) on the surface wettability of antismudge PU coatings were investigated. Among them, octadecyltrichlorosilane (OTS) terminated BHPDMS4300 exhibited the lowest water contact angle hysteresis (10.1°), which was even lower than that of the control samples via direct addition of monohydroxypropyl PDMS or BHPDMS4300. The antismudge PU coating also presented high transparency (90.5%) and excellent liquid repellency against various low surface tension liquids. Even after friction with steel wool, the coating can still maintain excellent antismudge performance. The results also showed enhancement of OTS on the liquid repellency of antismudge PU coatings, indicating its synergistic effect with BHPDMS brush. It is envisioned that OTS-terminated BHPDMS additive provides an avenue to fabricate cost-effective transparent antismudge PU coatings.