Improvement Of Grafting Efficiency Using Inimer In Seeded Emulsion Polymerization

This paper proposed a new method to raise the grafting efficiency in seeded emulsion polymerization. A high-graft-yield polymer with core-shell structure could be obtained by adding inimer during the seeded emulsion polymerization. The inimer contained both azo group, which can serve as initiator, and polymerizable vinyl group. By using the redox system at low temperature, azo group can be preserved and combine with the seed polymer network by chemical bond. During the shell monomer polymerization at high reaction temperature, "latent" azo group decomposed and produced free radicals, which could initiate the polymerization of the shell monomer, thus a high grafting rate core-shell structure polymer was prepared. The route was as follow:Firstly, we synthesized two kinds of inimer: acrylate-azo-bis(4-cyano) pentyl ester and methyl acrylate-azo-bis(4-cyano) pentyl ester at 0℃to 20℃, through the reaction of acryloyl chloride or methacryloyl chloride with azo-bis(4-cyano) pentanol in the presence oftriethylamine. ~1H NMR showed that the two-terminal products were 95% and 88％above respectively when the molar ratio of azo-bis(4-cyano) pentanol to acryloyl chloride or methaeryloyl chloride to be 2.5:1.Then, at low temperature, using persulphate / ferrous sulfate / white carved piece redox system, glycol acrylate ester as a crosslinker, SDBS as emulsifier, butyl acrylate monomer was polymerized in the presence of a small amount of inimer synthesized above, crosslinked acrylic latex seed containing azo group can be obtained. We discussed the effect of the emulsifier and crosslinker on the polymerization rate. It was found that the larger the amount of emulsifier added, the smaller the particle sizes generated and the faster the monomer polymerized, on the other hand the crosslinker had little influence on the polymerization rate.At last, methyl methacrylate was adding to the butyl acrylate seed latex, and then grafting polymerization was carried out at high temperature. Polymerization process had great effect on the particle sizes and sizes distribution. Further study found that: with the amount of crosslinker increased, the grafting rate increased and grafting efficiency reduced; when the content of the grafting monomer increased, the grafting rate and grafting efficiency decreased gradually. When the inimer was added, the grafting rate and grafting efficiency were greatly improved. This result is in good agreement with theory expectedness, as well as the innovation of this paper.