The Role of Nitroxide Degradation on the Efficiency of the Controller in Nitroxide-Mediated Radical Polymerization (NMP) of Styrene

Abstract

The effect of nitroxide degradation on polymerization rate and molar mass development in the nitroxide-mediated radical polymerization (NMP) of styrene is studied using electron spin resonance (ESR) spectroscopy and a mathematical model based on the method of moments. The stability of two nitroxides, 3,3-diphenyl-1,1-dimethyl azabutane N-oxide (azabutane) and 2,2,5-trimethyl-4-phenyl-azahexane N-oxide (TIPNO), is followed by ESR spectroscopy, and the products present in the final mixture are separated and analyzed. Significant nitroxide degradation is observed in both cases. The rate of azabutane degradation is about 100 times faster than that of TIPNO. Although a degradation mechanism is proposed, it is assumed in the model, for simplicity, that a new type of radical and a nitroso compound are produced. This new radical can propagate and terminate. Its participation is properly addressed in the polymerization scheme and its corresponding model. The model is validated using experimental data of styrene polymerization mediated by alkoxyamines derived from azabutane and TIPNO at 120 °C. Azabutane degradation significantly affects polymerization rate, initial molar mass, and end-group functionality of the polymer. The model provides a good representation of the effect of nitroxide degradation on NMP of styrene.

Modelling of polymerization kinetics and molar mass development in the nitroxide‐mediated polymerization (NMP) of styrene in supercritical carbon dioxide using the PC‐SAFT equation of state

“…The detailed kinetic equations for material balances of low and high molar mass species have been reported previously in publications from our group and are not included here. [26,30] There are three polymer populations in NMP: active or free radical polymer molecules, R ψ s ð Þ, dormant polymer molecules, PON x,ψ s ð Þ, and inactive or dead polymer molecules, P ψ s ð Þ, of size s = 1,2, …, ∞. [26] A large number of ordinary differential equations (ODEs) must be solved to calculate full polymer molar mass distributions for each polymer population.…”

“…[26,30] There are three polymer populations in NMP: active or free radical polymer molecules, R ψ s ð Þ, dormant polymer molecules, PON x,ψ s ð Þ, and inactive or dead polymer molecules, P ψ s ð Þ, of size s = 1,2, …, ∞. [26] A large number of ordinary differential equations (ODEs) must be solved to calculate full polymer molar mass distributions for each polymer population. The estimation of average properties for each polymer population is enormously simplified if the method of moments, as defined by Equations ( 5)-( 7), is used.…”

“…The detailed kinetic equations for material balances of low and high molar mass species have been reported previously in publications from our group and are not included here. [ 26,30 ]…”

“…There are three polymer populations in NMP: active or free radical polymer molecules, , dormant polymer molecules, , and inactive or dead polymer molecules, , of size s = 1,2, …, ∞. [ 26 ] A large number of ordinary differential equations (ODEs) must be solved to calculate full polymer molar mass distributions for each polymer population.…”

“…[20,21] The main approaches for the modelling of NMP processes include the method of moments, kinetic Monte Carlo, and the Predici ® software. [22][23][24] Some recent modelling studies addressing NMP include the production of polymer networks in the presence of NMP controllers, [25] NMP considering nitroxide degradation, [26] microwave-activated NMP, [27] optimization of temperature trajectories in NMP, [28] chain-length dependent termination in NMP carried out in continuous stirred tank reactors (CSTRs), [29] and bimolecular NMP. [30,31] Predici ® has also been used to study the NMP of Sty using 2,2,5-trimethyl-4-phenyl-3-azahexane-3-nitroxide (TIPNO) in scCO 2 at 110 C. [32] In this work, the development of a mathematical model for the kinetics and molar mass development in the NMP of Sty in scCO 2 is presented.…”