Study On The Formation Of Polymer Microspheres In Precipitation Polymerization

In recent years, polymeric microspheres are full of vitality and one of the importantfields having potential application. It has obtained a rapid development and caused thedomestic and foreign scholars more and more attention. Polymeric microsphere is theexcellent new functional material, and it has the outstanding performance with broadapplication. Among available methods, precipitation polymerization is of specific interestbecause micron-sized microspheres without use of any stabilizers or surfactants can beobtained. Monodisperse P（TMPTA-St） microspheres were prepared by precipitationpolymerization in our lab with styrene （St） as the main monomer, trihydroxymethyl propyltriacrylate （TMPTA） as cross-linker and azobisisobutyronitrile （AIBN） as initiator in ethanolrecently. Based on this work, polymeric microspheres P（TMPTA-MMA） microspheres wereprepared by precipitation polymerization with methyl methacrylate （MMA） as the mainmonomer which polarity and water-soluble is larger than St. The influence of the mixedsolvents on polymer microspheres formation was studied. The main results are listed asfollows.In ethanol-water mixture solvents, monodisperse microspheres were prepared throughprecipitation polymerization of TMPTA–MMA with AIBN as initiator. The polymermicrospheres prepared were characterized. Results showed that, in precipitationpolymerization of TMPTA-MMA, microspheres were achieved when TMPTA amounts waskept at0wt%⁸0wt%relative to the total mass of monomers, waters was0vol%⁴0vol%relative to the amount of mixture solvents. With increase of TMPTA amounts or water contentin the solvent mixture within the aforementioned range, monomer conversion was enhancedeffectively. In precipitation polymerization of TMPTA-MMA, keeping80wt%TMPTA,40vol%water in ethanol-water mixture solvents,2wt%AIBN, and the polymerization wascarried out under shaking rate at120osc./min at70oC for6h, uniform microspheres wereachieved. At the same time, the monomer conversion reached up to98%.Keeping TMPTA amounts at80wt%in precipitation polymerization of TMPTA-MMA,adjusting the composition of the binary solvent mixtures, the continuous variations in thethree-dimensional solubility parameters were achieved. Precipitation polymerization was conducted with these binary solvents of designed solubility parameters. Themorphologies of the polymeric products obtained were observed. Results showed that inbinary solvent of acetone-methanol, methanol-ethanol, acetic acid-ethanol,methanol-acetonitrile, ethanol-acetonitrile, methanol-ethyl acetate, polymer microsphereswere obtained when the polar component of the solubility parameter （p） was between8.5¹2.3MPa^1/2, and the hydrogen bonding component （h） was between17.0²2.3MPa^1/2,corresponding the differences between the solubility parameters of the solvent mixture andthose of the monomers must be controlled in the range of4.3⁸.1MPa^1/2for Δ pand9.0¹4.3MPa^1/2for Δ h.Microspheres were obtained via precipitation polymerization with pentaerythritoltriacrylate （PETA） and St as monomers in binary mixture of solvents. By adjusting thecomposition of the binary solvent mixtures, the Hansen’s tridimensional solubilityparameters of the mixed solvent changed continuously. The polymer microspheres preparedwere characterized. Through examination on the formation of the yield microspheres andtridimensional solubility parameters of solvent, the following was concluded: To obtainmicrospheres, when the differences between the solubility parameters of the solvent mixtureand those of the monomers Δ pand Δ hwere controlled in the range of6.6¹3.8MPa^1/2and8.5³6.7MPa^1/2. While ddid not show perceptible variation, the morphology of microsphereswas decided by pand h.