The thermally initiated free-radical dispersion copolymerization of methyl methacrylate (MMA)and N,N-dimethylacrylamide (DMA) in supercritical carbon dioxide has been studied in thepresence of polysiloxane surfactants. The formation of a stable latex seems to be related to thepresence of at least one reactive end group in the surfactant macromolecule, thus suggestingthat anchoring of the stabilizer to the surface of the growing polymer particles occurs throughchemical grafting. In the case of a molar ratio of DMA to MMA lower than 0.40, microsphericalcopolymer particles with yields ranging from 81 to 97% were collected from batch polymerizationscarried out at 65 °C and 23-28 MPa using AIBN as an initiator and PDMS-mMA as a surfactant.The effect of conversion on the cumulative composition of the copolymer was investigated at a0.20 mol/mol DMA/MMA ratio, and this composition, determined through NMR analyses, wasfound to be roughly constant during the entire process and, at the adopted initial feed composition,to remain close to the initial monomer feed mixture. The effectiveness of the surfactantstabilization toward the growing polymer particles was found to be dependent both on theconcentration of the surfactant and on the amount of the hydrophilic monomer (DMA) withrespect to the hydrophobic one (MMA). The experimental results indicate that, by a properselection of the polymerization recipe, it is possible to prepare microspherical copolymer particleswith tunable swelling behavior in aqueous media.
|Numero di pagine||8|
|Rivista||INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH|
|Stato di pubblicazione||Published - 2003|
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