A contribution to the theory of emulsion polymerization

Abstract

AbstractThe polymerization curve in emulsion polymerization in presence of retarding substance was determined. The active concentration of the monomer in the vicinity of the growing radical was assumed constant, while the number of reacting particles was varied. The active concentration of the retardant in the vicinity of the reacting radical was assumed constant during the polymerization.The following relationship was derived for the decrease in monomer concentration: where −m, is the decrease in monomer concentration, k2 is the kinetic constant of the chain growth, (M) is the active concentration of the monomer in the vicinity of the growing radical, n is the concentration of all particles in the emulsion, V′t is the velocity of penetration of the initiator radical into the particles; the initiation velocity V′i(n – n1)/n, n1 is the concentration of reacting particles, i.e., of particles containing the growing polymer radical, V′r = nk3[R]; k3 is the constant of chain termination by a retardant molecule; V′in1/n is the velocity of termination by a primary radical, and t is polymerization time. For the polymerization with a constant number of particles we have where −m2 is the decrease in monomer concentration during the period of constant polymerization rate. In the presence of a large amount of retardant, when V′r ≫ 2V′i the decrease in monomer concentration is given by This equation shows that for these conditions the decrease in monomer concentration is independent of the number of polymerizing particles, but it is directly proportional to the initiation velocity, and inversely proportional to k3[R]. For the final period at the end of the polymerization, when it can no longer be assumed that the active concentration of the monomer in the vicinity of reacting radical is constant, the following formula was derived: where −m3 is the total decrease in monomer concentration during the period of (M) ≠ const.; N is the number of particles in unit volume of the aqueous phase, NA is Avogadro's number; (M0) is the active concentration of the monomer in the period of constant polymerization rate; and t3 is the time elapsed from the beginning of this period, i.e., total polymerization time minus time of constant (M).