Effect of surfactant concentration and monomer polarity on particle nucleation in emulsion step polymerization of dithiol with diene

Abstract

The dependence of the number of particles N p as a function of the surfactant concentration [S] is investigated for the step polymerization of dithiol-diene emulsions. A sigmoidal curve for log N p vs log [S] is found for a range of monomers regardless of their polarity. Above the critical micellar concentration (6-20 mM), a N p  [S] x relationship is established with an exponent x dependent on the polarity of the two co-monomers. When the two comonomers are highly water insoluble, x varies typically between 0.6 and 1. With two relatively water soluble comonomers, x is close to 0. When two co-monomers with contrasting water solubility are involved, the power dependence is more difficult to predict and ranges from 0 to 1, but high x value are generally found when one of the two monomers is highly hydrophobic. This overall trend can be reconciled with the behavior of a conventional emulsion radical chain polymerization.

Thiol‐ene emulsion step polymerization in a photochemical stirred tank reactor: Molecular weight, cyclization, and fragmentation

“…13 The first investigations showed that the number of polymer particles formed and the nucleation mechanism did not deviate significantly from the normal chain pathway. 14 By contrast, significantly different behaviors are expected regarding polymer MW (evolution throughout the reaction and distribution) and structures (linear, branched, cross-linked and cyclic products), for which very few data are currently available. 15 In contrast to chain polymerization, 16 linear step polymerization is characterized by the difficulty to obtain high MW polymers, which are formed only late in the reaction that is, at very high overall monomer conversions (>98%-99%).…”

“…Unlike other step polymerizations, the formation of high polymers is made possible by distinct characteristic features of the thiol‐ene chemistry: 12 the absence of by‐products, high polymerization rates at ambient temperature (for a wide range of monomers) and a water‐insensitive radical‐mediated polymerization mechanism 13 . The first investigations showed that the number of polymer particles formed and the nucleation mechanism did not deviate significantly from the normal chain pathway 14 . By contrast, significantly different behaviors are expected regarding polymer MW (evolution throughout the reaction and distribution) and structures (linear, branched, cross‐linked and cyclic products), for which very few data are currently available 15 …”