Preparation Of Thermo-Expansive Microspheres By Suspension Polymerization

Thermo-expansive microspheres have had wide applications over the past decade due to its excellent foaming performance, electrical insulation, solvent resistance, abrasion-proof and non-toxic properties. Currently, thermo-expansive microspheres are produced via suspension polymerization at high pressure and high temperature, which suffers from the disadvantages such as grand investiment of high-pressure equipments, high energy consumption and risk of unsafe operation. The microspheres can hardly sustain good performance due to the boiling and leaking of the hydrocarbon in microspheres at high temperature, leading to high production cost and environmental concernsIn this work, a low-temperature polymerization technology was developed at atmosphere pressure in a temperature range of 0℃-25℃, producing uniform microspheres with high expansion ratio and excellent foaming performance. The appropriate monomer formulation and the best technological conditions (e.g., stirring speed, reaction time, etc.) have been determined in this work. The thesis mainly covers following aspects:1) A series of redox initiators including peroxides ccombined amines or silanes were investigated and the effect of initiator on the microsphere expansion ratio was examined. The redox initiator of benzoyl peroxide /N,N-dimethyl toluidine was found to produce microspheres with high monomer conversion, great expansion ratio and excellent foaming performance.2) The effects of crosslinker and expanding agent on the performance of the microspheres were evaluated. A limited amount of crosslinker was found to have great influence on the expansion ratio and foaming temperature of the microspheres.3) The influence of monomer formulation and technological conditions on the performance of the microspheres was investigated. The optimum monomer formula and the best operation conditions were determined as follows:methyl methacrylate:N,N-dimethylacrylamide:hexafluorobutyl methacrylate:isobornyl methacrylate= 8:2:0.3:0.6; initiator concentration: 200 mg/150 μL; stirring speed:1100 r/min; reaction temperature:0℃ for 4 h followed by a natural increase of temperature to room temperature for 8h.