A new kinetic interpretation of the styrene microemulsion polymerization

Abstract

The polymerization of styrene initiated by potassium peroxodisulfate was conducted at 50 "C in oil-in-water microemulsions using sodium lauryl sulfate and 1-pentanol as emulsifier and cosurfactant, respectively. Based on the experimental findings that both particle size and molecular weight of the polymers are almost independent of styrene conversion and the initial initiator concentration, a kinetic scheme of the microemulsion polymerization of styrene is proposed, which assumes that (1) particle nucleation occurs in monomer-swollen micelles and almost all the radicals in the water phase enter the monomerswollen micelles and finally initiate polymerization therein, ( 2 ) with negligible radical termination in the water phase and (3) with negligible radical entry into the preformed polymer particles, and accordingly, (4) all chain-stopping events in the active polymer particles are chain transfer reactions to monomer. Based on this kinetic scheme, a simple kinetic model is proposed, which can explain fairly well the progress of styrene microemulsion polymerization in the initial stage.

Nitroxide‐Mediated Radical Polymerization in Microemulsion

“…The TEMPO-mediated polymerizations were indeed very slow, much slower than conventional (non-living) radical polymerizations carried out in microemulsion, where such significant increases in particle size are usually not observed. [44] Consistent with the above, Min and Matyjaszewski [27] observed that microemulsion polymerization of MMA using reverse ATRP resulted in larger particles than direct ATRP (the nucleation process is slower in reverse ATRP due to the slow decomposition of the organic initiator employed).…”

“…If polymerization were to occur in a monomer-swollen micelle or particle not containing any nitroxide, the MWD would be dictated by chain transfer to monomer, and polymer of MW of the order 10 6 g Á mol À1 would be obtained already at low conversion. [44,61] No such high MW polymer (i.e. bimodal MWD) was detected in the present study ( Figure 2).…”

“…Due to the extremely high number of monomer-swollen micelles (true for both a controlled/living and a conventional microemulsion polymerization), entry into or radical generation inside a monomer-swollen micelle already containing one radical is negligible. [44][45][46] In an NMP system, dissociation of an alkoxyamine generates one propagating radical and one nitroxide in the same monomer-swollen micelle, and deactivation occurs extremely rapidly in small particles due to the confined space effect, [47][48][49] resulting in a reduction in R p compared to the corresponding bulk system. An additional factor causing low R p is enhanced geminate termination of radicals generated in pairs by thermal (spontaneous) initiation of S (according to the bulk mechanism), [50] again due to the confined space effect.…”

Synthesis of Nanosized (<20 nm) Polymer Particles by Radical Polymerization in Miniemulsion Employing in situ Surfactant Formation

“…[47] The very small particle sizes in the present systems give rise to strong compartmentalization effects, i.e., segregation of propagating radicals, which suppresses bimolecular termination and allows the majority of the propagating radicals to grow until chain transfer to monomer occurs. This type of behavior is normal in emulsionand microemulsion polymerizations with sufficiently small particles, [48][49][50] but has also been observed in welldefined miniemulsion systems with small particles. [35] The smaller the particles, the smaller is the contribution of termination, and consequently a greater fraction of radicals propagate until chain transfer to monomer occurs, thus leading to higher molecular weight.…”

Block copolymer synthesis by controlled/living radical polymerisation in heterogeneous systems

“…The potential of microemulsion polymerisation has yet to be fully realised for solvophobic block copolymer syntheses, although the few published examples suggests that highly pure products can be obtained, 97,118 which may be a direct result of confinement effects, where termination and radical side reactions are suppressed. 154,155 Methods in which the monomer is initially soluble and the growing polymer precipitates can further simplify the polymerisation process i.e. dispersion and precipitation polymerisation.…”