Structure and surface properties of liquid crystalline fluoroalkyl polyacrylates: Role of the spacer

The organization of liquid crystalline fluorinated acrylate polymers has be en generally described so far in the literature in terms of phase segregati on between hydrogenated and fluorinated moieties within the polymer and pre ferential orientation induced by the backbone. However, little is known on the effects of the chemical composition on the properties of such fluorine- containing polymers. Our study was then focused on the role played by the s pacer group located in the side chain between the backbone and the fluorina ted segment and in particular, on the properties of poly[2-[[[[2-(perfluoro alkyl)ethyl]sulfonyl]methyl]amino]ethyl]acrylates (pASn). Surface and bulk organization of fluorinated side chains of those polymers were investigated by surface tension, X-ray scattering, and differential scanning calorimetr y measurements. Results were compared with those obtained with poly[(perflu oroalkyl)ethyl] acrylates (pAFn) of the same perfluoroalkyl chain lengths. A strong correlation between bulk organization and surface properties of ou r polymers could be established. Surprisingly, in the perfluorohexyl series , pAS6 with a N-methylsulfonamide spacer group was found to be organized in a crystalline lamellar structure whereas pAF6 was found to be amorphous. T his indicates that the introduction of a N-methylsulfonamide spacer group i n the side-chain allows the system to crystallize with a shorter -C6F13 flu orinated segment, whereas in the presence of methylene groups, an organizat ion is only present with a -C8F17 segment (pAF8). This was mainly attribute d to the strong dipole-dipole interaction between N-methylsulfonamide group s that tends to align the fluorinated segments in a lamellar structure that eventually crystallizes as long as the section of the N-alkylsulfonamide g roup does not induce steric hindrance.