Kinetics of polymerization of N‐tert‐butylacrylamide. Part II

Abstract

AbstractThe effect of ferric chloride on the kinetics of the radical polymerization of N‐tert‐butylacrylamide has been investigated in methanol solution at 25°C, with the use of 4,4′‐dicyano‐4,4′‐azodipentanoic acid as initiator. A shrinkage factor of 0.193 mmole polymerized for 1 mm contraction in a capillary of 1 mm diameter has been obtained from density measurements. In the absence of ferric chloride, rates of polymerization were found to be proportional to the concentration of monomer and to the square root of the initiator concentration. With ferric chloride present, the rate of polymerization becomes directly proportional to the initiator concentration and inversely proportional to the concentration of ferric salt. From measurements of the rates of production of ferrous iron, the specific rate constant of the initiation reaction has been found to be (1.8 ± 0.4) × 10−6sec−1 at 25°C, compared with a value of 7.63 × 10−8 sec−1 calculated from the kinetic data obtained with no ferric salt present. The value of the ratio kp/k4. where kp is the propagation coefficient and k4 is the velocity coefficient for termination by ferric chloride, has been calculated to be 6.0 × 10−4 at 25°C, which is considerably smaller than the value found for the ferric chloride‐terminated polymerization of acrylamide in water. This markedly lower value of kp/k4 has been attributed principally to the steric effect of the tert‐butyl group on the magnitude of kp.