Kinetic control of aqueous polymerization using radicals generated in different spin states

Abstract

Background: Magnetic fields can interact with liquid matter in a homogeneous and instantaneous way, without physical contact, independently of its temperature, pressure, and agitation degree, and without modifying recipes nor heat and mass transfer conditions. In addition, magnetic fields may affect the mechanisms of generation and termination of free radicals. This paper is devoted to the elucidation of the appropriate conditions needed to develop magnetic field effects for controlling the kinetics of polymerization of water soluble monomers. Methods: Thermal-and photochemically-initiated polymerizations were investigated at different initiator and monomer concentrations, temperatures, viscosities, and magnetic field intensities. Results: Significant magnetic field impact on the polymerization kinetics was only observed in photochemically-initiated polymerizations carried out in viscous media and performed at relatively low magnetic field intensity. Magnetic field effects were absent in polymerizations in low viscosity media and thermally-initiated polymerizations performed at low and high magnetic field intensities. The effects were explained in terms of the radical pair mechanism for intersystem crossing of spin states. Conclusion: Polymerization kinetics of water soluble monomers can be potentially controlled using magnetic fields only under very specific reaction conditions.

Role of External Field in Polymerization: Mechanism and Kinetics

“…From the viewpoint of reaction kinetics, magnetic effects on a chemical reaction can be expressed by different values of pre-exponential factor ( A ) if different magnetic properties (i.e., singlet and triplet states) are involved in a rate-determining reaction step, whose rate coefficient ( k ) is given by the Arrhenius equation . Rintoul and co-workers have done a systematic study on the kinetic insights into the interplay of reactions (i.e., initiation, propagation, and termination) and magnetokinetic effects using the free radical polymerization of AM as the model system. , By carefully examining the reaction conditions, the reactions involving radical–radical interaction, namely, initiation and termination, exhibited significant magnetokinetic effects, while the magnetic effect on the propagation was negligible in this system. These results could be interpreted by a radical pair mechanism.…”

“…810 Rintoul and co-workers have done a systematic study on the kinetic insights into the interplay of reactions (i.e., initiation, propagation, and termination) and magnetokinetic effects using the free radical polymerization of AM as the model system. 844,845 By carefully examining the reaction conditions, the reactions involving radical−radical interaction, namely, initiation and termination, exhibited significant magnetokinetic effects, while the magnetic effect on the propagation was negligible in this system. These results could be interpreted by a radical pair mechanism.…”

Hydrophobically associating polymers for enhanced oil recovery – Part A: A review on the effects of some key reservoir conditions

“…As mentioned earlier, the method of synthesizing HAPAM polymers significantly influences the hydrophobe distribution on the polymer chain. The chemical synthesis of polyacrylamide is via a free radical polymerization (Giz et al, 2001;Qavi et al 2014;Rintoul, 2017;Yamamoto et al, 2017;Shatat and Niazi, 2018). Notwithstanding, the insoluble nature of the hydrophobic comonomer has led to the chemical modification of the synthesis route for HAPAM polymers (Zhang et al, 2017).…”

High chain-end fidelity in sono-RAFT polymerization

“…This calls for the development of polymerization techniques initiated by external stimuli and carried out at ambient temperatures. The use of external stimuli such as light, [5][6][7][8] microwave, 9,10 ultrasound, [11][12][13][14][15][16][17][18][19][20] electric field [21][22][23] and magnetic field 24,25 to initiate polymerization has piqued the interest of many researchers. [26][27][28] Ultrasound refers to sound waves with frequencies >20 kHz.…”