Redox-initiated adiabatic emulsion polymerization

In this dissertation research, n-butyl methacrylate (BMA) was used as the monomer in a model system employing redox initiators (ascorbic acid and H2O2) with sodium lauryl sulfate (SLS) as surfactant. A Mettler RC1 reactor calorimeter was used to study the reaction under isothermal and adiabatic conditions.;First, isothermal potassium persulfate (KPS)-initiated as well as redox-initiated batch emulsion polymerization processes were carried out to study the influence of different initiators as well as that of other conditions on the kinetics of emulsion polymerization. In the redox-initiated process, 7 mM of sodium chloride (NaCl) was added to increase the electrolyte concentration in the emulsion system, which controls the viscosity of the latex, and ferrous sulfate (FeSO4) was used as catalyst to enhance the radical generation rate.;The high radical flux resulting from the use of redox initiators (25 °C) leads to the formation of latexes with much smaller particle size, lower molecular weight and faster reaction rate compared with KPS-initiated thermal emulsion polymerizations (70 °C). Furthermore, in Interval II of the emulsion polymerization process, the reaction rate continued to increase in the case of redox-initiated polymerization, and the reaction rate is constant for the KPS-initiated emulsion polymerization. Those differences are due to the high radical flux induced by the redox initiators. Particle size is increased with lower surfactant concentration and lower initiator concentration. Molecular weight is higher with higher surfactant concentration and lower initiator concentration, and is not influenced significantly by changes in the solids content. TEM imaging in conjunction with a negative staining technique was used for particle sizing. Based on the reaction rates and the relationships between particle number and surfactant/initiator concentrations and solids contents, it has been demonstrated that micellar nucleation is the main nucleation mechanism for the KPS-initiated system, and both micellar nucleation and homogeneous nucleation play important roles in the redox-initiated system, which is further proved by the observed increase in particle number during the polymerization in the redox-initiated system.;Further, the surface tension of the aqueous phase obtained from the redox-initiated and KPS-initiated latex systems was measured by the Du Nuoy ring method. The free SLS concentration in the aqueous phase can be calculated from surface tension by using a calibration curve (surface tension vs. SLS concentration). The fractional surface coverage by SLS surfactant can be calculated. The high particle number in the redox-initiated latex results in lower free SLS concentration in the aqueous phase and lower fractional surface coverage compared with the KPS-intiated latex.;'Adiabatic' batch emulsion polymerization was then carried out in a Mettler RC1 reaction calorimeter under distillation mode, and the reaction heat was utilized to increase the reactor temperature and shorten the cycle time. Under 'adiabatic' conditions, the latex exhibits a larger particle size without significant change in molecular weight compared with the latex produced using redox initiator under isothermal conditions at the same starting temperatures. Seeded semi-batch polymerizations were carried out to study the influence of redox/KPS initiators and isothermal/adiabatic conditions. The particle size and conversion increased during the monomer feed process, with a high fractional conversion during the polymerization. The particle number remains constant during the polymerization, showing that secondary nucleation is eliminated. (Abstract shortened by UMI.).