Process for production of polymer powders containing vinylformamide units

Abstract

A process for producing a polymer powder comprising vinylformamide units by free radical polymerization of an aqueous solution of N-vinylformamide and if appropriate other monomers and drying the polymer which comprises an aqueous monomer solution comprising N-vinylformamide and at least one polymerization initiator being spray dispensed as an aerosol or dropletized at the top of a heatable tower-shaped reactor, then polymerizing the aerosol or droplets in an inert gas atmosphere to form a finely divided solid and discharging the finely divided polymer from the reactor.

1 . A process for producing a polymer powder comprising vinylformamide units by free radical polymerization of an aqueous solution of N-vinylformamide and if appropriate other monomers and drying the polymer, which comprises an aqueous monomer solution comprising N-vinylformamide and at least one polymerization initiator being spray dispensed as an aerosol or dropletized at the top of a heatable tower-shaped reactor, then polymerizing the aerosol or droplets in an inert gas atmosphere to form a finely divided solid and discharging the finely divided polymer from the reactor. 
     
     
         2 . The process according to  claim 1  wherein the reactor is fed in its upper third with an inert gas stream having a temperature of at least 100° C. 
     
     
         3 . The process according to  claim 1  wherein the temperature of the inert gas stream is in the range from 120 to 300° C. 
     
     
         4 . The process according to  claim 1  wherein the aqueous monomer solution is dropletized by means of a dropletizer plate disposed at the top of the reactor. 
     
     
         5 . The process according to  claim 4  wherein the dropletizer plate has drilled holes having a diameter in the range from 50 to 1000 μm. 
     
     
         6 . The process according to  claim 4  wherein the dropletizer plate is coated with or consists of a fluorous polymer. 
     
     
         7 . The process according to  claim 1  wherein the droplets of the aerosol formed by spray dispensing the aqueous monomer solution have a particle diameter in the range from 20 to 200 μm. 
     
     
         8 . The process according to  claim 1  wherein the droplets of the aqueous monomer solution which are formed by dropletization have an average particle diameter in the range from 100 to 2000 μm. 
     
     
         9 . The process according to  claim 1  wherein the aqueous monomer solution comprises N-vinylformamide as sole monomer. 
     
     
         10 . The process according to  claim 1  wherein the aqueous monomer solution comprises at least 50 mol % of N-vinylformamide and up to 50 mol % of at least one other water-soluble monomer. 
     
     
         11 . The process according to  claim 1  wherein the aqueous monomer solution comprises 0.001 to 10 mol % of at least one crosslinker having at least two double bonds in the molecule. 
     
     
         12 . The process according to  claim 1  wherein the aqueous monomer solution is adjusted with a phosphate buffer to a pH in the range from 5 to 7. 
     
     
         13 . The process according to  claim 1  wherein the aqueous monomer solution further comprises a polymerization regulator. 
     
     
         14 . The process according  claim 1  wherein the pulverulent polymer is subsequently agglomerated in a fluidized bed.