Attainment of Water and Oil Repellency for Engineering Thermoplastics without Long-Chain Perfluoroalkyls: Perfluoropolyether-Based Triblock Polyester Additives

Abstract

For decades, water and oil repellency of engineering thermoplastics has been achieved with introduction of long-chain perfluoroalkyl substances and moieties (C n F2n+1, n ≥ 7). However, their bioaccumulative and toxicological impact is now widely recognized and, consequently, the substances have been phased out of industrial production and applications. To this end, we have synthesized fluorinated oligomeric triblock polyesters (FOPBs), which do not possess the long-chain perfluoroalkyl segments and serve as effective low-surface-energy additives to engineering thermoplastics. More specifically, we obtained original perfluoropolyether (PFPE)-based triblock copolymers, in which two identical fluorinated blocks were separated by a short nonfluorinated polyester block made of poly­(ethylene isophthalate) (PEI). It was found that when FOPBs were added to poly­(ethylene terephthalate), nylon-6, and poly­(methyl methacrylate) films they readily migrate to the film surface and in doing so imparted significant water and oil repellency to the thermoplastic boundary. The water/oil wettability of the films modified with FOPB is considerably lower than the wettability of the films modified with an analogous PFPE-based polyester, which differs from FOPB only by the absence of the short nonfluorinated PEI middle block. We associate the superiority of the triblock copolymers in terms of water and oil repellency with their ability to form brushlike structures on polymer film surfaces.

Towards a Long-Chain Perfluoroalkyl Replacement: Water and Oil Repellent Perfluoropolyether-Based Polyurethane Oligomers

“…To this end, perfluoropolyether derived (co)polymers and cross-linked materials have been shown in our previous works and that of others to have the ability to serve as hydrophobic/lyophobic materials and interfaces [20][21][22][23][25][26][27][28][29][30][31][32][33][34][35][36][37]. In particular, we have found that when PFPE-based triblock polyesters [20,21,37] or methacrylic molecular brushes [36] are added to engineering thermoplastic (PET, nylon 6, or polymethyl methacrylate) films, they readily migrate to the film surface, imparting significant water and oil repellency to the thermoplastic boundary. Specifically, the macromolecular additives populated the boundary with PFPE segments terminated with C 4 F 9 -perfluoroalkyl moiety, which cannot yield unsafe long-chain perfluoroalkyl carboxylic acids.…”

“…The difference could be connected to the surface energy of the repeating units constituting macromolecular chains. To this end, we estimated surface energies and their (polar and dispersive) components (SI: S6) for the molecular segments constituting FOPUs using algorithms reported elsewhere [20,36]. The calculated values are presented in SI, Table S4.…”

“…The surface energy values estimated from the contact angle of hexadecane are close, but to some extent different from the ones obtained by the Owens-Wendt method utilizing both WCA and HDCA. We associate this difference with the differences in the size of the wetting liquids, which plays a significant role in the wettability of polymer surfaces [20,21,36]. Based on molecular weight and chemical structure, the size of water molecule is about an order of magnitude smaller than that of hexadecane.…”

“…AFM phase images (Figure 4) were employed to clarify this matter, since they are particularly sensitive to heterogeneity in surface composition [20,74]. The phase images did not show the top surface layer as discontinuous and only partially covering the film surface.…”

“…PFPEs are macromolecules possessing -CF 2 -, -CF 2 -CF 2 -, and -CF(CF 3 ) -CF 2 -molecular fragments in their Polymers 2021, 13, 1128 2 of 12 backbone that are separated by oxygen atoms. Currently, PFPEs are considered as potentially safer replacements for LCPFAs [3,[19][20][21]. PFPEs have numerous advantages, such as high chemical inertness and radiation resistance, low surface tension (20-22 mN/m) [22], nonflammability, low toxicity, optical transparency, and low volatility [22][23][24].…”