A mixed surfactant for controlling particle size of fluoropolymer emulsion and method for preparing fluoropolymer

Abstract

The invention discloses a mixed surfactant for controlling the particle size of a fluorine-containing polymer emulsion and a method of preparing a fluorine-containing polymer therewith. The mixed surfactant is composed of any two or three selected from perfluoropolyether carboxylic acid, perfluoro fatty acid and low-molecular-weight perfluoropolyether. By using the mixed surfactant in water-phase polymerization of the fluorine-containing polymer, the particle size of the fluorine-containing polymer emulsion is controlled to be 50-150 nm and solid content of the emulsion is controlled to be 25-35. In addition, a reaction solution for preparing the fluorine-containing polymer with the mixed surfactant is homogeneous-phase, so that pre-emulsion before polymerization is unnecessary. The mixed surfactant can be applied in a fluorinated monomer emulsion polymerization reaction instead of perfluoroctanoic acid, thereby avoiding the problems of environment pollution, biotoxicity and the like due to usage of the perfluoroctanoic acid.

Description

technical field [0001] The invention relates to the field of synthesis of fluorine-containing polymers, in particular to a mixed surfactant used in the field of synthesis of fluorine-containing polymers. Background technique [0002] Perfluoropolymer emulsion uses perfluorooctanoic acid or its salt as an emulsifier in the production process, and the particle size of the emulsion is above 100nm. PFOA has a stable molecular structure and excellent surface properties, followed by strong thermal stability and kinetic stability. Therefore, PFOA is considered to be persistent, bioaccumulative and toxic, and is a suspected human carcinogen. In 2006, the EPA issued a restriction decree, arguing that perfluorooctanoic acid ammonium (PFOA) and some chemicals that can be decomposed to produce PFOA are likely to cause major diseases such as cancer due to their high stability and refractory properties. [0003] In emulsion polymerization, the diameter and distribution of latex particles...

AI Technical Summary

Problems solved by technology

1. Increasing the polymerization stirring speed can reduce the particle size of the emulsion, but too fast stirring speed will cause demulsification, make the polymerization conditions change suddenly, and lead to the termination of the reaction

2. Seed pre-emulsification polymerization, the particle size of the emulsion gradually increases during the polymerization process, it is necessary to control the reaction time, the amount of monomer to control the particle size, the process is more cumbersome

3. The amphoteric emulsifier compound can control the particle size of the emulsion within a certain range, but the existing compound emulsifiers are mostly alkyl sulfonates and alkyl polyethers, which are easily oxidized at high temperatures, resulting in fluorine-containing polymer emulsions In the subsequent processing process, the color changes and the stability deteriorates. The existing technology is not suitable for the fluorine-containing emulsion polymerization process.

[0006] Other patents CN101903421 and CN103204961 disclose the use of mixed fluorosurfactants to prepare fluoropolymers, but both do not mention that the mixed surfactants used can adjust the particle size of fluoropolymer emulsions