Kinetic study of the polymerization of N,N′‐methylenebis(acrylamide) in aqueous dispersion systems

Abstract

AbstractThe aqueous‐phase polymerization of N,N′‐methylenebis(acrylamide) initiated by potassium peroxodisulfate in the absence and in the presence of the anionic emulsifier sodium dodecylsulfate was kinetically investigated at 50°C by conventional gravimetric and dilatometric methods. The rate of polymerization is found to be proportional to the 0,75 and 0,24 oder with respect to potassium peroxodisulfate and N,N′‐methylenebis(acrylamide) concentrations, respectively. On the other hand, it is independent of the concentration of sodium dodecylsulfate. This agrees with the polymerization of a monomer soluble in water. Therefore, the equations for a homogeneous polymerization were applied to evaluate the experimental results. The calculated ratio kp/kt0,5 of the rate constants of propagation kp and termination kt for the N,N′‐methylenebis(acrylamide) polymerization at zero conversion in the absence of emulsifier are scattered in the interval between 3,1 and 3,4 dm1,5 · mol−0,5 · s−0,5 and in the presence of emulsifier in the interval between 2,4 and 3,5 dm1,5 · mol−0,5 · s−0,5. They are close to those obtained for the homogeneous polymerization of acrylamide in the aqueous phase. The lower values of kp/kt0,5 ≈ 0,3–0,6 dm1,5 · mol−0,5 · s−0,5 determined for the polymerization of N,N′‐methylenebis(acrylamide) for conversions between 30 and 60% follow from the hindered termination reaction within the polymer particles. The polymer dispersions formed are unstable. The growth of the polymer particles proceeds predominantly by coalescence. This suggests a kinetics which does not follow the Smith‐Ewart theory but is characterized by a continuous particle nucleation and agglomeration. The interval 1 occurs at the beginning of the dispersion polymerization when polymer particles are being formed. Interval 2 follows, once the number of polymer particles has been fixed.