A study of the mechanism of emulsion polymerization of styrene and chloroprene by means of reaction heat

Investigation of the polymerization process was carried out on emulsions placed in water‐thermostatted flasks. The temperatures of the central part of the flask and of the thermostat were measured with the aid of thermocouples. The heat balance of the reaction system under investigation is given by the differential equation: The quantity of heat dq evolved during the time dτ in the course of the reaction raises the temperature of the system by d(ΔT), part of the heat being removed by the cooling bath. The constant K expresses the overall heat transfer, and C is the overall heat capacity of the polymerizing system. The left side of eq. (1) contains the time function of the reaction. We investigated the cases for zero‐, first‐, and second‐order reactions and derived the corresponding solution of the basic equation for ΔT = f(τ). For a zero‐order reaction: For a first‐order reaction: For a second‐order reaction: K0, K1, and K2 in eqs. (2), (3), and (4) are the zero‐, first‐, and second‐order rate constants, respectively, ΔH is the heat of polymerization; Mp and ΔTp, the number of moles and the temperature difference at the start of the reaction, respectively; the difference is the so‐called reduced exponential integral. The constants K and C may be calculated from the experimental curve ΔT = f(τ) and from two–three value for the degree of conversion in the course of polymerization. From this any number of values may be obtained for the degrees of conversion with time. For such values we derived the relation where Δp/Δτ is the overall reaction rate expressed by the increase with time of the amount of polymer. Expression (5) has a convenient linear plot, and from the slope and the intercept on the ordinate axis the reaction order i and the rate constant Ki may be determined directly. The theory was applied to a kinetic study of the emulsion polymerisation and styrene and chloroprene. An aqueous solution of potassion laurate served as emulsifier and potassium persulfate as initiator. The reaction was carried out at 40°C. The method permits accurate determination of the overall polymerization rate and of the monomer concentration in the latex particles. In a number of experiments the reaction rates and quantity of latex particles as function of initiator concentration were determined. The results were compared with conclusions following from the Smith‐Ewart quantitative theory of emulsion polymerization. The constants of chain growth of polystyrene and polychloroprene were determined.