Retardation kinetics in polymerization and depolymerization processes

Abstract

A kinetic analysis of retardation of polymerization and depolymerization reactions has been carried out. Using the derived expressions the validity of the current methods of determining rates of chain initiation from retardation data has been examined. Correlation of the theoretical expressions with experimental results is discussed.

Control of gel time and exotherm behaviour during cure of unsaturated polyester resins

“…For active scavengers, the polymerization is effectively delayed until [X] approaches zero 4. 21 Therefore, from eqn 11 the polymerization induction time is given by This equation is similar to that derived by other workers11–13 but it specifically includes the concentrations of the three main species–inhibitor, initiator and accelerator.…”

“…If the inhibitor is efficient (ie the rate of inhibition is fast compared with the rate of radical production) and the loss of radicals by bimolecular termination can be ignored, then radicals produced by the mechanism in eqns 3 and 4 will be almost immediately consumed by inhibitor (eqn 7) and a steady‐state concentration of radicals will exist. Thus the rate of change in radical concentration will be and so Thus the rate of loss of inhibitor, as shown by the reaction in eqn 7, is given by4, 21 When the inhibitor is finally consumed, the polymerization reaction can commence. Thus the induction, as shown in the initial stages of the exotherm curves in Figs 2 and 3, is controlled by this inhibition reaction.…”

“…Thus the induction, as shown in the initial stages of the exotherm curves in Figs 2 and 3, is controlled by this inhibition reaction. For an isothermal polymerization (which applies to the early stages of the experiment) and assuming that the initiator is not significantly depleted, eqn 10 shows that the inhibitor concentration will decrease with time, according to4, 21 where [X] 0 is the initial concentration of inhibitor. For active scavengers, the polymerization is effectively delayed until [X] approaches zero 4.…”

Determination of the Concentration of Intermediaries and of Rate Constants in Radical Reactions.

“…Under these circum- stances, it is common practice to extrapolate the steady-rate portion of the curve to the time axis and assume that the intercept on that axis gives the time for complete removal of the retarder. Burnett and Cowley (46) have concluded, from a kinetic analysis of the problem, that such a procedure is valid if the ratio of the rate constant for the interaction of radicals and retarder and the propagation constants is much in excess of 100. Further, the plot of the reciprocal rate against time leads to a value of the rate of initiation which is much more precise than that obtained by the more usual extrapolation procedure.…”