Preparation and Properties of Thermoplastic Expandable Microspheres with P(AN-MMA) Shell

Abstract

Thermoplastic expandable microspheres (TEMs) having a core/shell structure were prepared via suspension polymerization with acrylonitrile (AN) and methyl methacrylate (MMA) as monomers and i-butane as blowing agent. The relationship between monomer compositions and expansion properties of the TEMs was explored. When the weight ratio of AN and MMA is 1: 1, suspension polymerization could yield TEMs having good expansion properties and heat stability at 120–130°C. The maximum expansion volume is 22.5 times of the original volume. The temperatures at the maximum expansion volume (T_m.e.), at the onsets of expansion (T_o.e.) and the onset of shrinkage (T_o.s.) are 80, 120–130, and 145°C, respectively. The micromorphologies were observed by polarizing optical microscope (POM), the results show that the TEMs have a core/shell structure. The blowing agent content in TEMs is–20 wt %, which was determined by thermogravimetric analysis (TGA). Dynamic light-scattering (DLS) measurements show that the TEMs have an average particle size of–20 μm and a wide particle size distribution. The presence of low-molecular alcohol in water phase could help to reduce the particle size distribution.