Suspension polymerization of thermally expandable microspheres using low-temperature initiators

Thermally expandable microspheres were prepared by suspension polymerization using low-temperature initiators. The copolymer shells were made from acrylonitrile (AN) and methyl methacrylate (MMA) as the major monomers. Methacrylonitrile (MAN) was used as the third monomer to improve the expansion performance of the microspheres. This study investigated the influences of the initiator species, polymerization temperature, initiator content, and polymerization pressure on the expansion performance. Stable expandable microcapsules and good thermal characteristics were obtained successfully using 1.5 wt% azobis(4-methoxy-2.4- dimethyl valeronitrile) (V-70) as an initiator at a low temperature of 35 A degrees C and at polymerization pressure of 3 bar. The resulting particle size without destruction and secondary nucleation showed a mean diameter of 30 mu m under the optimal conditions. The encapsulated contents of the blowing agent were confirmed by thermogravimetric analysis (TGA) to be 40%.