Directly polymerized low molecular weight granular polytetrafluoroethylene

Abstract

A process for producing low molecular weight, granular polytetrafluoroethylene or modified polytetrafluoroethylene by suspension polymerization of pressurized tetrafluoroethylene in an agitated reaction vessel. The polymerization is conducted in aqueous medium in the presence of a free radical initiator, and a telogen. The reaction vessel is agitated during polymerization sufficiently to coagulate the polytetrafluoroethylene or modified polytetrafluoroethylene. Low molecular weight granular polytetrafluoroethylene or modified polytetrafluoroethylene having a melt viscosity of less than about 1×10 6 Pa·S powder is isolated directly from the reaction vessel. The low molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene powder in accordance with the invention has a melt viscosity of less than about 1×10 6 Pa·S, a specific surface area of less than about 8 m 2 /g, an extractable fluoride level of about 3 ppm or less by weight, and a narrow molecular weight distribution as indicated by a polydispersity index of about 5 or less. The particles of low molecular powder have a weight average particle size of about 2 to about 40 micrometers and the powder is substantially free of particles having a particle size of less than about 1 micrometer. The low molecular weight material so produced suitable for use as additives to other materials such as inks, coatings, greases, lubricants, and plastics.

1 . Low molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene powder having a melt viscosity of less than about 1×10 6  Pa·S, a specific surface area of less than about 8m 2 /g, an extractable fluoride level of 3 ppm or less by weight, a polydispersity index of about 5 or less and wherein the particles of low molecular powder have a weight average particle size of about 2 to about 40 micrometers and the powder is substantially free of particles having a particle size of less than about 1 micrometer.  
     
     
         2 . The low molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene powder of  claim 1  wherein said particles have a D90/D10 particle size distribution ratio of about 2 to about 10.  
     
     
         3 . The low molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene powder of  claim 1  wherein said melt viscosity is in the range of about 1×10 2  Pa·S to about 1×10 6  Pa·S.  
     
     
         4 . The low molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene powder of  claim 1  wherein said extractable fluoride level is 1 ppm or less by weight.  
     
     
         5 . The low molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene powder of  claim 1  wherein said specific surface area is less than about 5m 2 /g.  
     
     
         6 . The low molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene powder of  claim 1  wherein said polydispersity index is about 4.5 or less.  
     
     
         7 . The low molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene powder of  claim 1  wherein said polydispersity index is about 4.0 or less.  
     
     
         8 . An additive to ink compositions comprising the low molecular weight powder of polytetrafluoroethylene or modified polytetrafluoroethylene of  claim 1 .  
     
     
         9 . An additive to plastic compositions comprising the low molecular weight powder of polytetrafluoroethylene or modified polytetrafluoroethylene of  claim 1.