Diblock fluoroacrylate copolymers from two initiators: synthesis, self-assembly and surface properties

Abstract

Diblock fluoroacrylate copolymers poly(methyl methacrylate) (PMMA)-b-poly(dodecafluoroheptyl methacrylate) (PMMA-b-PDFHM) for coating materials are synthesized via atom transfer radical polymerization (ATRP) by two different initiators, a brominated initiator end group terminated by 1H,1H,2H,2H-heptadecafluoro (F–Br) and the conventional initiator ethyl 2-bromoisobutyrate (EBiB). The copolymer structures are characterized by 1H NMR, 19F NMR and GPC analyses. The influence of the two initiators on the self-assembly behavior and the surface properties of PMMA-b-PDFHM films are explored. Because of the divergent solubility of the segments in chloroform (CHCl3), tetrahydrofuran (THF) and trifluorotoluene (TFT) solutions, the self-assembly of PMMA-b-PDFHM in CHCl3, THF and TFT was investigated using dynamic light scattering (DLS) and transmission electron microscopy (TEM). Accordingly, the properties of PMMA-b-PDFHM films cast from CHCl3, THF and TFT solutions were compared for their surface wettability, surface free energy, surface elemental composition, surface morphology and roughness, and surface water adsorption, through analysis of static contact angle (SCA), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and quartz crystal microbalance with dissipation (QCM-D). It is found that the copolymers F-PMMA-b-PDFHM using F–Br initiator and E-PMMA-b-PDFHM using EBIB initiator, reveal both unimers (7–9 nm) and micelles (220–360 nm) in THF and CHCl3 solutions, which are recognized by TEM as dichroic half-spherical or core–shell particles, but occur mainly as unimers (5–9 nm) in TFT solution, which is favorable for obtaining films with low surface free energies. F-PMMA-b-PDFHM films show lower surface free energy (17.1–17.7 mN m−1) than E-PMMA-b-PDFHM films (17.9–22.9 mN m−1) in each solvent. The surface morphology and roughness determined are strongly controlled by the cast solutions. F-PMMA-b-PDFHM films exhibit a low wettability and high stable surface due to a well-ordered fluorocarbon surface provided by both PDFHM and F–Br groups, and therefore can be developed into a high-performance coating material.