An Error in Variables Method for Determining the Implicit Penultimate Copolymerization Ratios by On‐Line Monitoring of Reactions

Summary: In copolymerization systems with implicit penultimate effect, there are two radical reactivity ratios, s_a and s_b, which influence the reaction kinetics in addition to the monomer reactivity ratios, r_a and r_b, which govern the copolymer composition. Here, an error in variables method has been developed to determine s_a and s_b. It is based on continuous on‐line monitoring of the polymerization process, where monomer and polymer concentrations are measured through the monitoring of two independent properties of the system. The ratios and the corresponding χ² values were found by taking into account errors emanating from measurements and from calibration of the instruments. It is shown that the kinetic data allows both ratios to be found if both monomer reactivity ratios are less than one. If the system is near ideality (r_ar_b ? 1) or if both reactivities are greater than one, only an average radical reactivity ratio, , can be reliably determined.

The 2σ confidence contours for the 3 individual experiments. The reactivity ratios are r_a = 0.5, r_b = 0.2, s_a = 0.3, s_b = 0.4. For clarity the contours are plotted as functions of 1/s_a and 1/s_b.