Kinetics of Chain Depolymerization

Pyrolysis of anionic and thermally prepared polystyrenes

“…The values of the other ratios involving k2, k~, k3 and k~ also shown in table 3 are estimated using the value of a, x and the monomer yield, 40 percent. It is seen that the zip length, kinetic chain length, A, and the ratio of transfer to initiation, (T, a parameter used in previous treatments [1,2,13,27], are all dependent on the degree of polymerization. In figure 13 At Pn = 200, Z = 7 for pure monomer.…”

“…Some time ago a theory [1,2] 1 was developed for the thermal degradation of those polymers that undergo pure chain bond ruptures and hence in an open system are completely volatilized. The mechanism assumed was comprised of four elementary free radical processes: initiation, propagation, intermolecular transfer, and termination.…”

“…At the time, long kinetic chain lengths were anticipated in many polymer decompositions [5,6] and for such situations the method of bimolec ular termination is of small consequence. Also, termination can be actually effectively first order if the degree of polymerization is shorter than the zip [1,2] or kinetic chain length. A recent study of the decomposition of polytetrafluoroethylene [7] has, however, demonstrated that the mechanism for this polymer has a short zip length with termination mainly by combination.…”

“…One criticism of the earlier treatment [1,2] that is not totally valid since some monodisperse polymers can now be prepared by appropriate polymerization techniques, has been that existing polymeric materials are polydisperse. Since the assumption that a "most probable" distribution exists in many polymers and is maintained throughout the degradation process simplifies the theoretical treatment, several efforts in this area were made [8,9].…”

“…Until recently the shapes of the experimental thermal volatilization curves for polystyrene have not been produced by a fully a priori theory. However, with the use of computer evaluation the original theory [1,2] was shown [13] to be able to nearly reproduce the experimental rate and molecular weight behavior. The results indicate that intermolecular transfe r, end initiation, and zip lengths of the order of 5 are operative.…”