Influence of catalyst depletion or deactivation on polymerization kinetics. III. Solution polymerization of acrylonitrile in N,N‐dimethylformamide at −30°C.

Abstract

AbstractThe experimental results on homogeneous polymerization of acrylonitrile initiated with the sodium triethylthioisopropoxyaluminate, NaAlEt3S(i‐Pr), catalyst in DMF at −30°C. are compared with the prediction of equations based on a postulated mechanism. The agreement between the calculated and observed number‐average molecular weight combined with the kinetic data and the relationship between the conversion and the initial catalyst concentration provides a rigorous test concerning the validity of the equations and the mechanism of the polymerization. A plausible mechanism is postulated as follows: The initiation must be relatively fast in accordance with the rate equations and the growing polymer undergoes propagation, transfer (to monomer), and deactivation simultaneously. The infrared spectrum of the low molecular weight polymer prepared at a high catalyst concentration showed strong absorption at 2337, 2205, and 1620 cm.−1 but no absorption at 900 cm.−1, indicating that there are two nitriles in the polymer, one of which is conjugated. The possibility of having CHCH2 groups in the polymer is ruled out by the absence of the band at 900 cm.−1. In view of these facts, it is concluded that the polymer has a CHCHCN endgroup resulting from the transfer reaction.