Self-crosslinking borate anions for the production of tough UV-cured polyelectrolyte surfaces

The first anion with four polymerizable groups has been synthesized and used to produce durable, crosslinked polyelectrolyte (PE) coatings in a single step. Sodium tetrakis(4‐vinylphenyl)borate (NaBSty4) was produced by the reaction of BCl3 and the Grignard of 4‐bromostyrene. The full series of borates NaBPhxSty4−x, x = 1−3, were also synthesized analogously by reaction of the styryl‐Grignard and PhBCl2, Ph2BCl, or Ph3B. Anion exchange of the borates with tributyl 4‐vinylbenzylphosphonium chloride gave a family of organic salts developed for applications in photopolymerized coatings. The percent UV cure of the polymer films was determined by infrared spectroscopy and this relative level of curing was corroborated by differential scanning calorimetry analysis. The degree of crosslinking imparted to the polymer films by the different monomers has resulted in varied mechanical properties, which were probed by diamond tip scratch tests and nanoindentation. These clearly demonstrated that as the number of polymerizable groups increased, the film hardness increased correspondingly. The final hardness of the films exceeds those of other related systems and identifies styryl borates as viable crosslinking additives in UV curable technologies, especially in the production of durable PE films. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 Tough polyelectrolyte coatings have been produced in a single step by UV‐curing novel phosphonium‐borate monomers. The new tetrakis(styryl)borate anion enables high crosslink density upon rapid photopolymerization. The full series of borates NaBPhxSty4− x, x = 0−3, have also been prepared and incorporated into the phosphonium borate salt monomers. As the number of styrene groups in the monomer increases, the polymer films become more mechanically resilient. Analysis by nanoindentation showed an increase in the film hardness while scratch tests showed an increased scratch resistance of the polyelectrolyte surface.