Compartmentalization in Nitroxide-Mediated Radical Polymerization in Dispersed Systems

Abstract

Modified Smith-Ewart equations were used to quantitatively investigate compartmentalization effects in nitroxide-mediated radical polymerization in dispersed systems. Calculations were carried out for the specific system 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO)/styrene at 125 °C with thermal initiation included in the model, and accounting for compartmentalization of both propagating radicals and nitroxide. For particles with diameter (d) less than approximately 60 nm, a reduction in particle size led to lower rate of polymerization, higher degree of livingness, and a higher number of activation-deactivation cycles experienced per chain to grow to a given degree of polymerization. These effects have their origin in the pseudo first-order deactivation rate coefficient increasing in proportion to d -3 with decreasing particle size. There were no significant effects of compartmentalization for particles with d > 110 nm. The results show that it is important to consider compartmentalization effects also on the deactivation reaction, and not only bimolecular termination.

Threshold Particle Diameters in Miniemulsion Reversible-Deactivation Radical Polymerization

“…Such cases are found when k 2 /k t is small, i.e., in a bad living condition [14]. Because the bimolecular termination is significant in bulk polymerization in such cases, the segregation of radicals into different polymer particles [6] reduces the termination frequency. Reduced termination frequency slows down the accumulation of the trapping agents in a particle.…”

“…For SRMP and ATRP, theoretical calculation results have shown that a particle size region may exist in which the polymerization rate is larger than bulk polymerization [6][7][8][9][10][11][12][13][14], which was named the acceleration window [10]. Figure 2 shows a typical example.…”

Atom transfer radical polymerization in aqueous dispersed media

“…Compartmentalization is an intrinsic feature of polymerization in dispersed systems [16], and it affects the polymerization in two ways: a segregation effect and a confined space effect [73]. The former effect refers to a fact that two radicals located in separate particles cannot react together, i.e., a termination rate is decreased.…”

“…Recent modeling results show that significant compartmentalization effect requires a small particle size [73]. However, experimental evidence of compartmentalization effect on CRPs in aqueous dispersed media is still not clear [74].…”

Controlled/living heterogeneous radical polymerization in supercritical carbon dioxide

“…Radical polymerization in heterogeneous systems is more complex than homogeneous systems due to various mechanistic aspects, e.g., entry/exit events and compartmentalization, 30 as well as aspects related to colloidal stability. For example, the extent of nitroxide partitioning to the continuous phase may affect NMP in heterogeneous systems, 31 and for sufficiently small particles, the deactivation rate may increase due to the confined space effect 32,33 (deactivation of a propagating radical occurring rapidly in a confined space). These intrinsic features of heterogeneous systems can ideally be exploited-for example, it is in some cases possible to improve the control/livingness in NMP and ATRP 34,35 by exploiting the confined space effect on deactivation by use of sufficiently small particles.…”