Ultrasonically Initiated Free Radical-Catalyzed Emulsion Polymerization of Methyl Methacrylate (I)
The emulsion polymerization of methyl methacrylate initiated by ultrasound has been studied at ambient temperature using sodium lauryl sulfate as the surfactant. the investigation includes the: (1) nature and source of the free radical for the initiation process; (2) effects of different types of cavitation; and (3) dependence of the polymerization rate, polymer particle number generated, and the polymer molecular weight on acoustic intensity, argon gas flow rate, surfactant concentration, and initial monomer concentration. It was found that the polymerization could be initiated by ultrasound in the emulsion systems containing methyl methacrylate, water, and sodium lauryl sulfate at ambient temperature in the absence of a conventional initiator. the source of the free radical for the initiation process was found to come from the degradation of the sodium lauryl sulfate, presumably in the aqueous phase. the weight average molecular weight of the poly(methyl methacrylate) obtained varied from 2,500,000 to 3,500,000 g mol-1, and the conversion for polymerization was up to 70%. Deviations from the Smith-Ewart kinetics were observed. the polymerization rate was found to be proportional to the acoustic intensity to the 0.98 power; to the argon gas flow rate to the 0.086 power; to the surfactant concentration to the 0.08 power, with the 0.035M-0.139M surfactant concentration range; and to the surfactant concentration to the 0.58 power, with the 0.139M-0.243M surfactant concentration range. the polymerization rate was found to increase with increasing initial monomer concentration up to a point where it became independent of initial monomer concentration. the polymer particle number generated per milliliter of water was found to be proportional to the acoustic intensity to the 1.23 power; to the argon gas flow rate to the 0.16 power; to the surfactant concentration to the 0.3 power, with the 0.035M-0.139M surfactant concentration range; and to the surfactant concentration to the 1.87 power, with the 0.139M-0.243M surfactant concentration range. the polymer weight average molecular weight was found to be proportional to the acoustic intensity to the 0.21 power, and to the argon gas flow rate to the 0.02 power. It was found to be inversely proportional to the surfactant concentration to the 0.12 and 0.34 power, with the 0.035M-0.139M and the 0.139M-0.243M surfactant concentration ranges, respectively. the polymer yield and polymerization rate were found to be much larger than those obtained from an ultrasonically initiated bulk polymerization method. the polymerization rates obtained at ambient temperature were found to be similar to or higher than those obtained from the conventional higher temperature thermal emulsion polymerization method. This investigation demonstrated the capability of ultrasound to both initiate and accelerate polymerization in the emulsion system, and to do this at a lower temperature that could offer substantial energy savings. © 1999 John Wiley & Sons, Inc.
H. C. Chou and J. O. Stoffer, "Ultrasonically Initiated Free Radical-Catalyzed Emulsion Polymerization of Methyl Methacrylate (I)," Journal of Applied Polymer Science, Wiley-Blackwell, Jan 1999.
The definitive version is available at https://doi.org/10.1002/(SICI)1097-4628(19990509)72:6<797
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