Method of making silicone emulsions having low residual volatile siloxane oligomer content

Abstract

A batch steam distillation process removes volatile siloxane oligomers from an emulsion containing siloxane polymers and volatile siloxane oligomers prepared by emulsion polymerization of volatile siloxane oligomers. In one embodiment, emulsions stripped of volatile siloxane oligomers are re-catalyzed to initiate condensation polymerization. In another embodiment, clear emulsions stripped of volatile siloxane oligomers are provided even though an antifoam is used in the stripping process.

1 . A method of preparing an aqueous emulsion containing particles of siloxane polymer of an average size less than 0.1 micron/100 nanometer comprising: 
 (I) heating and emulsion polymerizing a mixture containing a volatile siloxane oligomer or mixture of volatile siloxane oligomers, at least one anionic surfactant or cationic surfactant, optionally a nonionic surfactant, water, and an emulsion polymerization catalyst or mixture of emulsion polymerization catalysts;    (II) neutralizing the emulsion polymerization catalyst;    (III) adding an antifoam composition to the neutralized emulsion in (II) at a concentration of 0.01-20 weight parts of active antifoam per million weight parts of the emulsion;    (IV) stripping the emulsion using steam until the emulsion contains less than 0.18 parts by weight of volatile siloxane oligomer per unit weight of the siloxane polymer in the emulsion, and the fraction of light at a wavelength of 580 nanometer transmitted though the emulsion exceeds 70 percent.    
     
     
         2 . A method according to  claim 1  where the steam in (III) is generated in situ.  
     
     
         3 . A method according to  claim 1  where the steam in (III) is fed into the emulsion from an external source.  
     
     
         4 . An emulsion prepared according to the method defined in  claim 1 .  
     
     
         5 . A method of treating a surface or substrate selected from the group consisting of hair, skin, paper, and textile, comprising applying to the surface or substrate the emulsion prepared according to the method defined in  claim 1.