Aqueous emulsion polymerization of fluorinated monomers using a perfluoropolyether surfactant

Abstract

The invention relates to an aqueous emulsion polymerization of fluorinated monomers using perfluoropolyethers of the following formula (I) or (II). In particular, the perfluoropolyether surfactants correspond to formula (I) or (II) CF3—(OCF2)m—O—CF2—X  (I) wherein m has a value of 1 to 6 and X represents a carboxylic acid group or salt thereof, CF3—O—(CF2)3—(OCF(CF3)—CF2)z—O-L-Y  (II) wherein z has a value of 0, 1, 2 or 3, L represents a divalent linking group selected from —CF(CF3)—, —CF2— and —CF2CF2— and Y represents a carboxylic acid group or salt thereof. The invention further relates to an aqueous dispersion of a fluoropolymer having the aforementioned perfluoropolyether surfactant(s).

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] This application claims priority to Great Britain Patent Application No. GBO514387.0, filed on Jul. 15, 2005, herein incorporated by reference in its entirety. [0002] The present invention relates to the aqueous emulsion polymerization of fluorinated monomers to produce fluoropolymers. BACKGROUND OF THE INVENTION [0003] Fluoropolymers, i.e. polymers having a fluorinated backbone, have been long known and have been used in a variety of applications because of several desirable properties such as heat resistance, chemical resistance, weatherability, UV-stability etc. The various fluoropolymers are for example described in “Modern Fluoropolymers”, edited by John Scheirs, Wiley Science 1997. Commonly known or commercially employed fluoropolymers include polytetrafluoroethylene (PTFE), copolymers of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) (FEP polymers), perfluoroalkoxy copolymers (PFA), ethylene-tetrafluoroethylene (ETFE) cop...

AI Technical Summary

Benefits of technology

[0017] It would now be desirable to find an alternative emulsion polymerization process in which the use of perfluoroalkanoic acids and salts thereof as a fluorinated surfactant can be avoided. In particular, it would be desirable to find an alternative surfactant or dispersant, in particular one that is more environmentally friendly, for example has a low toxicity and / or shows no or only little bioaccumulation. It would also be desirable that the alternative surfactant has good chemical and thermal stability enabling polymerization over a wide range of conditions of for example temperature and / or pressure. Desirably, the alternative surfactant or dispersant allows for a high polymerization rate, good dispersion stability, good yields, good copolymerization properties and / or the possibility of obtaining a wide variety of particle sizes including small particle sizes. The properties of the resulting fluoropolymer should generally not be negatively influenced and preferably would be improved. Desirably, the resulting dispersions have good or excellent properties in coating applications and / or impregnation of substrates, including for example good film forming properties. It would further be desirable that the polymerization can be carried out in a convenient and cost effective way, preferably using equipment commonly used in the aqueous emulsion polymerization of fluorinated monomers. Additionally, it may be desirable to recover the alternative surfactant or dispersant from waste water streams and / or to remove or recover the surfactant from the dispersion subsequent to the polymerization. Desirably, such recovery can proceed in an easy, convenient and cost effective way.

Problems solved by technology

However, environmental concerns have been raised against these surfactants and moreover these surfactants are generally expensive.

It is taught that the perfluoropolyether surfactants on their own are not very powerful surfactants.