Comparative study on random and block fluorinated polyacrylates for fabrication of hydrophobic 2K polyurethane clearcoats

In this study, 2-(perfluorohexyl)ethyl methacrylate, hydroxyethyl methacrylate and methyl methacrylate were used to synthesize three random fluorinated polyacrylates with various fluorine contents (i.e., F1H1, F3H1, and F5H1) and one block fluorinated polyacrylate (i.e., PFPHM) through traditional radical polymerization and atom transfer radical polymerization, respectively. These copolymers were further adopted as hydrophobic additives to incorporate into 2K polyurethane (PU) clearcoats. Effect of the type and dosage of the fluorinated polyacrylate on the haze, surface hydrophobicity, outdoor hydrophobicity durability and dirt pick-up resistance (DPUR) of modified coatings were investigated. Fluorinated polyacrylate additive with higher fluorine content is easier to cause haze of 2K PU clearcoats, nevertheless, hydrophobic surface could be acquired at lower dosage, alleviating its negative effect on transparency. PFPHM showed extremely higher hydrophobicity modification efficiency compared to the random polyacrylate additive, due to its easy enrichment at the superficial layer of 2K PU clearcoats. Moreover, PFPHM-modified 2K PU coatings presented the best hydrophobicity durability and dirt pick-up resistance in outdoor exposure test. The loss of hydrophobicity outdoors was mainly due to the aging of PU matrix, loss of fluoroalkyl chains, and partially to the dirt adhesion.