Effects of the high side-chain densities of hydrophobic poly(substituted methylene)s on their surface free energies

All the carbon atoms in the main chains of poly(substituted methylene)s possess side chains. The densities and chemical structures of the side chains drastically change the polymers’ thermal, mechanical, and surface properties. Herein, we focused on the surface properties and structures of poly(substituted methylene)s with hydrophobic side chains of ethyl and perfluoroalkyl groups and evaluated the effects of their side-chain densities. The surface free energy of poly(substituted methylene) with ethyl groups, C1-PEA, was lower than that of poly(ethyl acrylate) because the high density of the side chains in C1-PEA decreased its chain mobility, and the dispersion component of its surface free energy was also suppressed. The surface free energy of poly(substituted methylene) with perfluoroalkyl groups containing only six carbon atoms in each fluoroalkyl group, C1-PF, was less than 10 mJ/m2. In addition, the surface segregation of the perfluoroalkyl groups in the block-like copolymer and the greater hydrophobic properties of this polymer were observed compared to the corresponding random copolymer. The C1-PEA polymers showed dependence of their surface free energies and structures on their respective preparation methods. Highly dense side chains facilitated the restriction of molecular chains and greater hydrophobic surface properties. Poly(substituted methylene)s possess higher dense side chains and their chain mobilities are restricted, relative to conventional vinyl polymers. The surface of poly(substituted methylene)s was more hydrophobic. In particular, the poly(substituted methylene) with perfluoroalkyl groups showed lower surface free energy than the corresponding vinyl polymer. Moreover, the surface of block-like copolymer of poly(substituted methylene) was more hydrophobic than that of random copolymer. The preparation methods of films of poly(substituted methylene) with ethyl ester side chains controlled their surface free energies and structures.