علوم و تکنولوژی پلیمر (Jan 2013)
Synthesis of Polybutadiene Particles via Emulsion Polymerization: Effect of Emulsifier and Initiator Contents on the Reaction Kinetics and Latex’s Particle Size
Abstract
Batch emulsion polymerization of butadiene was performed at 70°C in a Buchi reactor equipped with mechanical stirrer (300 rpm) in the presence of potassium persulfate (KPS), and disproportionate rosinate, potassium cation (DPR) as initiator and emulsifier, respectively. t-Dodecyl mercaptane was used as a chain transfer agent in polymerization reactions. Conversion was measured at various time intervals by gravimetry. Polymerization rate was then calculated from the slope of conversion versus time curves. Particle size and its distribution of the polybutadiene latex (PBL) were measured by dynamic light scattering (DLS) and scanning electron microscopy (SEM). Depending on the emulsion polymerization conditions, PBL latices were obtained with average particles’ diameter and particle size distribution in the range of 88.5-189 nm and 35-400 nm, respectively. The number of particles per unit volume of the continuous phase was calculated from the average particle size data, from which polymerization rate per particle or equally its number of growing chains per particle was evaluated. Results showed that by increasing the emulsifier concentration, the average particle size decreases while polymerization rate increases. Moreover, the number of growing chains per particle decreased slightly by increasing the emulsifier concentration. Unlike classic emulsion polymerization, particle size and polymerization rate were observed to be more or less independent of initiator concentration. The results obtained from investigation of the reaction trend showed that kinetics of the emulsion polymerization of butadiene follows case 1(n<<0/5) of the Smith-Ewart kinetics. The observed behaviour was attributed to the lower efficiency of initiator in the particle nucleation and growth processes.
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