Methods for studying radical polymerization.
Part l. Dilatometric determination of the initial stationary polymerization rate
Polimery 2001, No 11-12, 752
Methods are described for processing the primary dilatometric data to study the course of radical polymerization. The primary data include ρ(t), viz., the degree of monomer conversion (ρ) measured continuously as a function of time (t). The data processing methods include the graphical differentiation which is used to evaluate d[ρ(t)] / dt = f(t), the calculation of ρ(ti) / ti at the ith measurement followed by averaging of results, the calculation of Σp(t)/ΣΔt, which also averages the results, etc. These methods rely on an empirical assumption, viz., that at initial polymerization stages (yields < 10%,), the function ρ(t) = f(t) is rectilinear and the polymerization is described by a first-order (n = 1) kinetic equation. The empirical methods are shown to produce considerable errors in the calculation of the initial stationary, both uncorrelated (s-1) and correlated (mol · dm-3 · s-1), polymerization rate. A new method is suggested to process primary dilatometric data that is consistent with the kinetics of the process. Analytical integral equations are given (eqns. 10, 31, 33) that describe polymerization of the order (n) of 1, 3/2, or 2; for 1 < n < 2, approximate solutions are given (eqns. 37, 38). The left-hand side of each equation expresses directly the initial (stationary) rate of monomer depletion from its original concentration level, [M]0 When multiplied by [M]0 the left-hand sides of the equations express the correlated rates of polymerization, mol · dm-3 · s-1. The integral equations allow to establish the order of the polymerization reaction with respect to the monomer and also to disclose whether the order is dependent on, or independent from, [M]0. Studies on the classical and nonclassical kinetics (involving nanotubes SWCNT that modify both the kinetics of polymerization and the properties of products) in the polymerizations of acrylonitrile (AN) and methyl methacrylate (MMA) carried out in solutions of dimethylformamide (DMF) in the presence of various azo compound initiators (Figs. 1-4) are presented to illustrate the use of the integral equations.
Keywords: radical polymerization, kinetics of polymerization, dilatometry, data processing methods, vinyl monomers, acrylonitrile, methyl methacrylate, azo compound initiators