Control of various morphological changes of poly(meth)acrylate microspheres and their swelling degrees by SPG emulsification

Crosslinked poly(meth)acrylate polymers with a variety of morphologies were synthesized with two steps. In the first step, a microporous glass membran e (Shirasu Porous Glass, SPG) was employed to prepare uniform emulsion drop lets by applying an adequate pressure to the monomer phase, which was compo sed of the ADVN initiator, solvent of toluene or heptane or their mixture, and a mixture of (meth)acrylate monomers. The droplets were formed continuo usly through the membrane and suspended in the aqueous solution, which cont ained a PVA-127 suspending agent, SLS emulsifier, and NaNO2 inhibitor to su ppress the nucleation of secondary particles. SPG pore sizes of 0.90, 5.25, and 9.25 mum were used. Then the emulsion droplets were polymerized at 343 K with a rotation rate 160 rpm for 24 h. The (meth)acrylate monomers 2-eth ylhexyl acrylate (2-EHA), 2-ethylhexyl methacrylate (2-EHMA), cyclohexyl ac rylate (CHA), methyl methacrylate (MMA), lauryl acrylate (LA), and lauryl m ethacrylate (LMA) were used in this research. The influences of the ratios of the monomer and crosslinking agent EGDMA, the amount of diluents, the mo nomer type on the polymer particle morphology, the swelling degree, and the polymer particle size were investigated. It was found that an increase in the concentrations of EGDMA and heptane resulted in higher coarse porous sp heres and smaller polymer particle sizes. A coefficient with a variation cl ose to 10%, or a standard deviation of about 4, was obtained. The capacity of these spheres as solvent absorption materials was examined. The highest swelling degrees of heptane and toluene were obtained when LA was employed as the monomer with 30% (by weight) of EGDMA and 70% (by weight) of heptane as an inert solvent. The highest capacity of the solvent absorption was ob tained when using a polymer particle size of 4.81 mum, as prepared by SPG p ore size 0.9 mum. The polymer particles were able to absorb aliphatic hydro carbon solvents, aromatic hydrocarbon solvents, and a mix of aliphatic hydr ocarbon solvents and aromatic hydrocarbon solvents, such as toluene and hep tane. The capacity of solvent absorption for the aromatic hydrocarbon solve nts was higher than for the aliphatic hydrocarbon solvents. In addition, th e particles did not rupture or collapse after absorption in solvents. (C) 2 000 John Wiley & Sons, Inc.