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 (Tm.e.), at the onsets of expansion (To.e.) and the onset of shrinkage (To.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.