| 摘要 |
Very low molecular weight polymers are sometimes used in toners which are designed for high speed printers and copiers. It is extremely difficult to prepare polymers having the ultra-low molecular weights required in such applications by standard emulsion polymerization techniques. By utilizing the techniques of this invention, the molecular weight of polymers made by conventional emulsion polymerization can be reduced to a very low level. This invention more specifically discloses a process for preparing a low molecular weight polymer which is particularly useful as a toner resin, which comprises (1) treating an emulsion of a polymer having a number average molecular weight which is within the range of about 18,000 to about 40,000 and which is comprised of repeat units which are derived from about 65 to about 95 weight percent of a vinyl aromatic monomer, from about 1 to about 12 weight percent of a conjugated diene monomer, and optionally from about 1 to about 34 weight percent of an alkyl acrylate monomer, with ozone in an amount and under conditions which are sufficient to reduce the number average molecular weight of the polymer to within the range of about 3,000 to about 15,000; and (2) recovering the polymer from the emulsion. |
