CORRELATION BETWEEN CRYSTALLIZATION BEHAVIOR OF FLUORINATED ACRYLATE COPOLYMERS AND THE SURFACE WETTING PROPERTY OF THEIR FILMS

Abstract

A series of fluorinated acrylate copolymers were synthesized via free radical copolymerization by using monomers of 2-(perflurooctyl)ethyl methacrylate(FOEMA) and n-alkyl acrylates(RAs)(n=4,8,12,16,18) with various lengths of side chains.The crystalline behavior of the copolymers was characterized by X-ray diffraction(XRD) and differential scanning calorimetry(DSC).It is found that the crystallization of acrylate copolymers is in close connection with the side-chain length of acrylates.The copolymers crystallized at room temperature when the side-chain length number n was 16 or 18,however,no crystallization was observed for the copolymers with n less than 16 under the same condition.The crystallization enthalpy changes of RA-co-FOEMA copolymers were determined from the DSC thermograms.The copolymer with n=16 has the minimum entropy change at constant pressure compared with other three crystallized copolymers through thermodynamic calculation,which indicated this copolymer was the most ordered one.The F/C atomic ratios and composition of functional groups on the surfaces of RA/FOEMA copolymer films were determined by multifunctional photoelectron spectroscopy(XPS),and the static contact angles of n-hexadecane and water on films were measured.The F/C ratios increased from 0.39 to 0.71 with increase in the side-chain length of RA/FOEMA copolymers.When n was 16 or 18,the copolymers demonstrated much more composition of non-polar groups(—CF3 and —CF2) and fewer polar groups(—C-O and —C—O—C-O) on the film surfaces,leading to the rapid increase in the n-hexadecane static contact angles on the films of copolymers.It may suggest that crystallization of hydrocarbon side-chain of copolymers can promote fluorinated component to migrate to the polymer-air interface during the process of film forming and hence improve the hydrophobicity and oleophobicity of the films.