Kinetic theory in regards to the basic understanding of reaction order as it relates to polymer degradation is discussed. This new theory is then tested by determining the kinetic parameters for dehydrochlorinated poly(vinyl chloride) using thermogravimetric analysis. Four different mechanisms of degradation were deduced from four sets of kinetic parameters. The calculated kinetic parameters were apparent reaction order, apparent activation energy, and apparent frequency factor as determined by the original Freeman and Carroll model. The four regions/mechanisms attained by the theory from the data are in order of appearance:  final dehydrochlorination; random chain scission; cyclization; coke degradation. The data indicate transition regions between the individual regions where two mechanisms are competing with one another. Also, a method for obtaining the optimal heating rate from a set of heating rates is discussed.

The statistical product distribution for a linear polydisperse polymer of finite molecular weight was included into the statistical analysis for a system undergoing random chain scission showing the effect of volatilization of species other than monomer. Two sets of equations were derived. One set is for the nonvolatile fraction; the other is for the volatile fraction. Within each set there are three equations, one for the number of polymer molecules, the second for the molar (or number) fraction, and the third for the weight fraction of polymer molecules containing a specific number of repeat units. As degradation proceeds the polydispersity index should converge to a value of 1 rather than 2, which has been reported previously. The expected effects of polydispersity, number‐average degree of polymerization, and volatility were treated individually, and we determined that the molecular weight of a polymer has no theoretical influence on the product distribution. As for the effect of volatility, we determined that only the volatile product distribution would change. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3690–3696, 2000