Expansion Characteristics of Expandable Styrene/Methyl Methacrylate Copolymer Beads: The Effects of Molecular Weight and Particle Size Distribution

A bead form foamable copolymer was synthesized by suspension polymerization of methyl methacrylate and styrene in the presence of a blowing agent. When the surrounding temperature was high enough to vaporize the blowing agent and soften the polymer shell, the copolymer beads were expanded due to pressure difference across the shell. The accurate investigations of the molecular and morphological properties of the beads showed that the expansion behavior of the expandable beads was dependent on molecular weight of the matrix polymer and particle size of the beads. The findings also suggested that the dimensional stability of the pre-expanded beads could be controlled by the molecular weight modifying aid concentration and copolymer molecular weight.