Cyclization kinetics of poly(acrylonitrile)

Experimental studies of poly(acrylonitrile) (PAN) homopolymer and itaconic acid co-polymer stabilization examine the impact of polymer composition, temperature and reaction environment on the rate of cyclization. Stabilization of homopolymer PAN in nitrogen, 10.5 and 21% oxygen produces sigmoidally shaped curves when extent of cyclization is plotted as a function of reaction time. The length of the initial induction period in the sigmoidally shaped homopolymer curves decreases with increasing temperature and when oxygen is present in the reaction environment. Co-polymer cyclization curves also exhibit an induction period when reacted in nitrogen, but the period is less distinct than in the homopolymer case. The length of the induction period in the co-polymer data decreases with increasing temperature and increasing acid concentration. In the presence of oxygen, no induction period is present in any of the acidic co-polymer data. Reactions in 10.5 or 21% oxygen result in retardation of PAN homopolymer and co-polymer cyclization relative to reaction in a nitrogen environment. The retarding effect of oxygen is minimized as the acid concentration in the polymer is increased.