Initiated Chemical Vapor Deposition (iCVD) of poly(alkyl acrylates): A kinetic model

In a two-part investigation, an experimental study and a kinetic model analysis of the initiated chemical vapor deposition (iCVD) of alkyl acrylate polymers are described. In this second part, a kinetic model was developed to examine the reaction mechanisms of iCVD polymerization. The model incorporated surface polymerization events of initiation, propagation, and termination as well as primary radical termination and recombination. By using a multiresponse parameter estimation procedure based on minimizing a determinant criterion, the model fitted closely to experimental data on butyl acrylate iCVD that measured the effect of a change in monomer surface concentration on both the rate of polymerization and polymer molecular weight. Model propagation and termination rate coefficients, 15 540 and 0.98 × 10 ⁶ L/mol·s, respectively, matched well with those of liquid-phase butyl acrylate radical polymerization, 15 460 and 10 ⁶ L/mol·s, respectively. The model captured the linear dependencies of rate and molecular weight to monomer concentration typical of liquid-phase radical polymerization. At low concentrations, the model further captured the nonlinear rate behavior, which was attributed to significant primary radical termination. Sensitivity analysis revealed a well-behaved model with model parameters that trended realistically. These results provided strong support for a surface-driven iCVD polymerization that is surprisingly analogous to bulk-phase free radical polymerization. A proven iCVD kinetic model would ultimately facilitate process scale-up and provide a priori predictions on the feasibility of new iCVD chemistries.