Wettability of Maleimide Copolymer Films:  Effect of the Chain Length of n-Alkyl Side Groups on the Solid Surface Tension

We report bulk and surface properties of maleimide copolymers with two different backbones, poly(propene-alt-N-(n-alkyl)maleimides) (PAlkMI) and poly(styrene-alt-N-(n-alkyl) maleimides) (SAlkMI), with different lengths of n-alkyl side chains (methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, and dodecyl). The contact angle and solid surface tension results suggest that, for the longer side chains, the surface properties are dominated by the side chains. Indeed, the surface tension of the two types of copolymers with length of the side chain above C = 6 are essentially equal, indicating complete shielding of the polar backbone chain. For the two copolymers containing dodecyl side chains, the solid surface tension is similar to that of solid surfaces consisting exclusively of CH3 groups. Apparently, these side groups are long enough to allow arrangement in the configuration of the lowest surface free energy possible for alkyl chains. For the short side chain copolymers the styrene compounds are more hydrophobic than the propene compounds. The bulkier phenyl rings shields the polar backbone chain more effectively than the small alkyl groups.