Process for the manufacture of fluoroelastomers having bromine or lodine atom cure sites

Abstract

Fluoroelastomers having bromine, iodine or both iodine and bromine cure sites are prepared by an emulsion polymerization process wherein any iodine or bromine containing comonomers and any iodine or bromine containing chain transfer agents are introduced to the reactor as aqueous emulsions, optionally containing a surfactant.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of U.S. Provisional Application No. 60 / 731,381 filed Oct. 28, 2005.FIELD OF THE INVENTION [0002] This invention relates to a process for the manufacture of fluoroelastomers having bromine, iodine or both bromine and iodine atom cure sites wherein the comonomer or chain transfer agent containing said bromine or iodine atoms is added to the polymerization reactor in the form of an aqueous emulsion. BACKGROUND OF THE INVENTION [0003] Fluoroelastomers having excellent heat resistance, oil resistance, and chemical resistance have been widely employed for sealing materials, containers, and hoses. Examples of fluoroelastomers include copolymers comprising units of vinylidene fluoride (VF2) and units of at least one other fluorine-containing monomer such as hexafluoropropylene (HFP), tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE), vinyl fluoride (VF) and fluoroethers such as a perfluoro(alkyl vinyl...

AI Technical Summary

Problems solved by technology

A general problem with the use of either iodine- or bromine-containing cure sites or comonomers is related to the generally high specific gravity of these compounds.

Because these materials settle to the reactor bottom, they may be incorporated unevenly into polymer chains such that a portion of the chains has an abnormally high amount of cure site while other portions have an abnormally low amount of cure site.

This will result in undesirable variability in the end use performance of products made from fluoroelastomers.

Another consequence of the high specific gravity is that a portion of the iodine- or bromine-containing compound may not even become incorporated into the polymer, resulting in reduced efficiency of the iodine- or bromine-containing compound, and the need for additional waste treatment facilities to capture any residual iodine- or bromine-containing cure site or chain transfer agent.

Yet another consequence of the high specific gravity is poor viscosity control of the resulting fluoroelastomer polymer, because the iodine- or bromine-containing chain transfer agent does not become evenly incorporated into the polymer chains.

Another problem with the use of many iodine- or bromine-containing cure site monomers or chain transfer agents is their lack of solubility in water.

In order to achieve complete incorporation of a poorly soluble chain transfer agent into a polymer, the overall polymerization rate may need to be decreased, which leads to an inefficient use of polymerization reactors.

However, this approach is unsatisfactory because it requires additional waste treatment facilities to remove the solvent from either the polymer or the waste water.

In addition, it is difficult to find satisfactory solvents that do not interfere with the polymerization reaction and slow it down.

However, this method has the drawback that the fluorinated oils that comprise the microemulsion are retained in the polymer.

These can be detected (e.g. by headspace GC-MS), and may adversely affect adhesion to metals and mill behavior, as well as food contact status.