On the modeling assessment of thermal styrene polymerization

In this work the problem of determining the dependencies on conversion of the initiation rate (R i ), the propagation (k p ), termination (k t ), and transfer to monomer (k tr ) kinetic constants in the thermally initiated free‐radical polymerization of styrene is addressed. A nonlinear observability analysis establishes that the parameter groupings R i , κ = k t /k   2 p , and C m = k tr /k p dependencies on conversion can be determined on the basis of the species conservation balances in conjunction with conversion and (number‐ and weight‐) average molecular weight experimental measurements, without making any a priori kinetic modeling assumption. Then, the differential estimation technique associated with the observability property is applied to previously reported experimental runs at 100, 120, 170, and 200°C, yielding the following results: (1) for the two lower temperature runs, R i exhibits a nearly quadratic dependency on monomer concentration, and for the higher temperature the overall dependency is about cubic or quartic, and this behavior differs from that of the standard cubic‐dependency model; (2) κ shows an exponential‐like decay with conversion that agrees with previous reports, and (3) C m exhibits a quadratic‐like increase with conversion that disagrees with the linear decay assumed before. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2246–2257, 2004