Effect of the addition of inert or TEMPO‐capped prepolymer on polymerization rate and molecular weight development in the nitroxide‐mediated radical polymerization of styrene

Abstract

ABSTRACT:The importance of diffusion-controlled (DC) effects on controlled radical polymerization (CRP) processes has been rather controversial and usually considered only if there is some mismatch between experimental data and model predictions of polymerization rate and molecular weight averages. Results from an experimental study designed to create conditions in which DC effects may be present from the outset for the bimolecular nitroxide-mediated radical polymerization (NMRP) of styrene in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and dibenzoyl peroxide (BPO), are presented herein. The experiments consisted of adding size exclusion chromatography (SEC) polystyrene (PS) standards or nitroxyl-capped PS (of different molecular weights, in several proportions), to a conventional recipe of bimolecular NMRP of styrene, and studying the effect of their presence on polymerization rate and molecular weight development. A previously developed kinetic model for NMRP of styrene was modified to take into account the presence of prepolymer as an inert ''solvent,'' or as a monomolecular ''controller'' of high molecular weight. The effects of DC reactions (propagation, termination, activation, and deactivation of polymer radicals) were modeled using conventional free-volume theory. Reasonably, good agreement between experimental data and model predictions with either modeling approach was obtained. It was concluded that DC effects are weak in the NMRP of styrene, even in the presence of prepolymer.

A complete understanding of the reaction kinetics for the industrial production process of expandable polystyrene

“…The (zeroth order) average apparent termination rate coefficient (definition: Table ; footnote c) thus decreases less, as can be seen in Figure S.7 in Supporting Information, an effect that is inherently incorporated in the (full) composite k t model as it takes the influence of the chain length on the mobility explicitly into account (entry 3 in Table ). Note that this weakening of the effect of diffusional limitations is in agreement with literature data for radical polymerization systems involving shorter chains …”

Effect of initiator type and concentration on polymerization rate and molecular weight in the bimolecular nitroxide‐mediated radical polymerization of styrene

“…After this period, the polymerization rate follows standard NMRP kinetics. More data on NMRP using BPO as initiator can be found in Nabifar et al, 20 who studied the effect of temperature and molar ratio between TEMPO and BPO on polymerization rate, molecular weight, and polydispersity and in Roa-Luna et al, 21 who studied diffusion effects in NMRP of styrene in the presence of TEMPO and BPO. On the other hand, TBEC has a relatively low decomposition rate at this temperature (k d = 0.017 min −1 ).…”

“…Figure 2b also shows that the molecular weights increase linearly with conversion, which is expected for a controlled polymerization process. In a Advances in Polymer Technology DOI 10.1002/adv bimolecular initiated system, it has been shown by Roa-Luna et al 21 that the true concentration of controller is difficult to assess because peroxide reacts with nitroxide and reduces the concentration of active TEMPO in the polymerization reaction. This is well evidenced for BPO, and it is likely that TBEC would lead to a similar outcome.…”

“…Roa-Luna et al 21 simulated a NMRP system considering a decrease in the effective TEMPO concentration, to consider potential reactions that can occur between initiator and controller. They found a higher polymerization rate at the beginning of the reaction, but no significant change was observed in the overall profile.…”

Substituent effects of accelerator on nitroxide-mediated radical polymerization

“…Up to now, several methods, such as atom transfer radical polymerization (ATRP), 1-7 nitroxide-mediated radical polymerization (NMRP), [8][9][10][11][12] reversible addition-fragmentation transfer polymerization (RAFT), [13][14][15][16][17][18][19] have been developed to synthesize well-defined polymers, including block polymer, [14][15][16]20,21 graft polymer, [22][23][24] star shaped [25][26][27][28][29][30] and hyperbranched polymer. [31][32][33][34] Among them, the NMRP is an attractive controlled polymerization system because it is metal free and effective in the polymerization of a broad range of monomers with various functionalities.…”