Molecular weight distribution in novolac-type polymerization in homogeneous, continuous-flow stirred tank reactors

Abstract

The kinetic model for irreversible novolac type phenol formaldehyde polymerization and equations governing the molecular weight distribution (MWD) of the polymer formed in homogeneous continuous-flow stirred tank reactors (HCSTR) have been derived. The set of algebraic equations involves three reaction parameters R₁, R₂, and R₃ and have been solved using Brown's algorithm which was found to be more efficient than the Gauss-Jordon technique of solution. A sensitivity analysis of different reaction parameters has been carried out and the reactivity of the para position was found to be an important factor affecting the MWD. In view of the fact that parameters R₁ and R₂ have a negligible effect on MWD, the phenomenon of molecular shielding described by Drumm et al. (1) can be neglected. The novolac formation can then be equivalently described by assuming R₁ = 1 and R₂ = R₃ and the kinetic description so obtained is completely based on the experimentally observed different reactivities of ortho and para sites. The results for HCSTR have been compared with those for batch reactors and the former is found to give polymer of lower average molecular weights having higher polydispersity index.