Continuous kinetics for thermal degradation of polymer in solution

Continuous kinetics of thermal degradation of poly(styrene-allyl alcohol) (PSA) in solution are explored theoretically and experimentally. Thermal degradation experiments for PSA of number-average molecular weight 1,640 in t-butanol solution were conducted in a steady-state flow reactor at 6.8 MPa and 403--473 K. The molecular-weight distributions (MWDs) of the original polymer and its reaction products were measured as a function of residence time by gel permeation chromatography. The MWD of the initial PSA is described by a gamma distribution function. Experimental data indicated that the polymer cracks to specific, low-molecular-weight (MW) products and degrades by random chain scission. Results are interpreted by a mathematical model based on the continuous kinetics for specific and random degradation processes. Rate coefficients are determined separately from the dynamic data of the MW moments for the specific products and the MWDs for the reacting polymer. Activation energies obtained are 5.9--7.4 kcal/mol for specific degradation processes and 35 kcal/mol for the random degradation process. The detailed MWDs are related to conventional lumped (number-average molecular-weight) data.