Microwave irradiation versus conventional heating assisted free-radical copolymerization in solution

Significance 

Microwave heating continues to attract significant attention as a promising alternative to conventional heating. It is environmentally friendly and generally suitable for both large-scale production and lab-scale research. The attractiveness of microwave heating technology can also be attributed to its capability to accelerate chemical reactions to achieve rapid transformation, increased yields and fewer byproducts. Microwave irradiation has been extensively applied in different chemistry fields, including materials, analytical and medicinal chemistry. However, its application in polymer synthesis has remained underexplored. The recent development of new microwave reactors with improved reaction parameters control has proved useful in enabling microwave-assisted polymerization to synthesize different polymers via either control radical polymerization or conventional free radical polymerization.

To date, several studies have been conducted to investigate the free-radical solution polymerization, providing a good avenue for comparing the performance of microwave and conventional heating assisted polymerizations. In most reaction conditions, microwave heating technology exhibited improved performance than conventional heating. Other studies, however, reported no significant differences between the two heating methods. For instance, the reported studies on the copolymerization of different monomers in different solvents produced no differences in the monomers studied. The controversial results have raised many questions on their reliability and validity. Despite the development of specialized microwave reactors, research shows that controlling the reaction temperature still requires double monitoring using sensory devices. These revelations provide a new understanding of the microwave effects that can be attributed to the thermal effects. Nonetheless, comparative experimental studies on the microwave and conventional heating-assisted polymerization processes are still lacking.

To this note, Dr. Bertha Pérez-Martínez, Professor José Ramon Leiza and Professor Radmila Tomovska from the University of the Basque Country UPV/EHU, in collaboration with Dr. Ali Aboudzadeh (Centro de Física de Materiales, CSIC-UPV/EHU,) and Professor Ulrich S. Schubert (Friedrich Schiller University Jena) performed both conventional heating and microwave irradiation assisted free-radical polymerization reactions in different organic solvents and in the presence of different initiators. The aim was to obtain reliable and comparable results. The original research article is found in the Chemical Engineering Journal.

In their approach, similar reaction conditions were created for both microwave and conventional heating reactors leveraging the advantages of the microwave reactor design, similar temperature profiles, and the condition of both the polymerization reactions. Copolymerization of different monomers with different dielectric properties and different polarities was studied in different organic solvent solutions using different initiators. Also, the effects of co-monomer systems, solvents, and initiators on the reaction rates and on the composition and properties of the copolymers were investigated.

The authors observed no changes in the molar masses, polymerization rates and polymer composition under similar reaction conditions for conventional heating and microwave irradiation reactors, for all studied monomer couples, contrary to some previous reports, where, mainly the enhancement in the reaction rate was observed. The exception from this happened in the presence of organometallic monomer in the monomer couple, where microwave irradiation exhibited an enhancement in the reaction rate as well as differences in the reactivity ratios and the copolymer compositions. This effect, also known as the specific microwave effect, was more pronounced in toluene since it was exposed to more microwave irradiation to maintain the same temperature profile.

In summary, the study reported a reliable comparison of microwave irradiation and conventional heating-assisted polymerization by creating similar reaction conditions. The interaction between the reaction components and the microwave irradiation was vital in determining any microwave irradiation effects on the reaction and resulting products. The microwave effects, demonstrated for the time in free-radical solution polymerization, were explained in detail via the heating properties of the microwave irradiation in the multi-component solution. From the comparisons of the energy consumption between the polymerization systems, the authors concluded that selecting appropriate solvent is crucial in saving energy without compromising the product quality. In a statement to Advances in Engineering, Professor Radmila Tomovska said the findings will advance future research on the effects of microwave irradiation in free-radical polymerization processes.

Microwave irradiation versus conventional heating assisted free-radical copolymerization in solution - Advances in Engineering

About the author

Bertha T. Pérez-Martínez earned her M.S in Chemistry Technology at the University Autonomous of Coahuila (Coahuila, México) in 2014. Her master thesis was focused on preparation of waterborne polymer/functionalized multiwalled carbon nanotubes composites, one part of which was performed at POLYMAT institute, under supervision of Prof. Jose M. Asua and Prof. Radmila Tomovska. After finishing the master studies, she realized six months research and training stay in the company Bioactive Ingredients S.A. de C.V. (México), followed by eighteen months training in the company KAPPA CENTER OF KNOWLEDGE S.C. (México), in the department of management and administration of business projects and transfer of technology. Since 2016 she started her PhD project on application of microwaves in polymer synthesis at POLYMAT institute, University of the Basque country under the supervision of Prof. Radmila Tomovska and under scholarship from the National Council of Science and Technology (CONACyT-México), defended in April of 2021.

About the author

M. Ali Aboudzadeh is currently a Marie Curie Fellow in IPREM, a joint research unit attached to the CNRS and the University of Pau and Pays de l’Adour, France. He received his BSc (2003) and MSc (2006) in Polymer Engineering from Amir Kabir University of Technology and Iran Polymer & Petrochemical Institute, respectively. He obtained his PhD (2015) in Applied Chemistry and Polymer Materials from University of the Basque Country, Spain. Dr. Aboudzadeh is author/coauthor of more than 25 professional papers in different research areas, including polymer synthesis and characterization; supramolecular assemblies; rheology; DNA nanotechnology; encapsulation via emulsion-based systems. He recently edited a book entitled “Emulsion‐based Encapsulation of Antioxidants” under the publisher “Springer”.

About the author

Ulrich S. Schubert studied chemistry in Frankfurt and Bayreuth (both Germany) and at Virginia Commonwealth University, Richmond (USA). After PhD studies at the Universities of Bayreuth and South Florida, and a postdoctoral training with nobel laureate J.‐M. Lehn, he moved to the TU Munich (Germany), where he obtained his Habilitation in 1999. 1999–2000 he was Professor at the University of Munich and 2000–2007 Full Professor at the TU Eindhoven (The Netherlands). Since 2007, he has been a Full Professor at the Friedrich Schiller University Jena (Germany). He is an elected member of the German National Academy of Science and Engineering (acatech) and external scientific member of the Max‐Planck‐Gesellschaft (MPI for Colloid & Interfaces, Golm). He is founding director of the Jena Center for Soft Mater (JCSM) and the Center for Energy and Environmental Chemistry Jena (CEEC Jena), spokesman of the DFG CRC 1278 (“PolyTarget”), coordinator of the DFG priority program “Polymer-based Batteries” (SPP 2248) and the EU ITN “POLYSTORAGE” (GA 860403). Prof. Schubert published so far more than 1100 refereed scientific publications, 4 textbooks and 55 patents. His h-Index is 107.

About the author

Jose Ramon Leiza is Professor of Chemical Engineering at the school of Chemistry of the University of the Basque Country (UPV/EHU). He graduated in Chemistry in 1987 and obtained the Ph.D. degree in Chemical Engineering in 1991 at UPV/EHU. He has served as Director of the Institute of Polymer Materials, POLYMAT, from 2011 to 2020.

He spent sabbatical years at Lehigh University (USA) as Visiting Research Associate (1994-95) and Queen’s University (Canada) as a Visiting Professor (2004-05).

Awards: Rhone-Poulenc award in Clean Technologies (1993). Association of Engineers of Madrid.

His current research interests are focused on the following topics: polymer reaction engineering aspects of polymerization in dispersed media (e.g., kinetics, modeling, high solids content formulations), waterborne polymer/inorganic hybrid nanocomposites for anticorrosion coatings, polymerization of water soluble monomers as additives for concrete, renewable resource monomers and their application for the production of novel adhesives and coatings, and electrospinning of polymer latexes.

He has published more than 180 papers, 20 book chapters and delivered 28 invited talks and more than 170 poster and oral presentations in international conferences. He has coauthored 9 patents and has supervised 25 PhDs. He is member of the editorial boards of the Macromolecular Reaction Engineering (2010-) and International Journal of Polymer Science (2008-2016) journals. He co-chaired and organized the International Polymer Colloids Group conference in 2017 (IPCG2017) and vice-chaired the Polymer Reaction Engineering conference (PRE10) in 2018.

About the author

Radmila Tomovska has got bachelor, master and PhD degree in chemical engineering from the Faculty of Technology and Metallurgy, University Sts. Cyril and Methodius, Macedonia. The PhD project was developed in close collaboration with the Extraction Laboratory, Institute of Process Fundamentals, Czech Academy of Sciences. During the postgraduate and doctoral studies, in continuation she was under fellowships from Macedonian Government. Since 2001 she obtained NATO postdoc fellowship for a research in UV and IR laser induced chemical reaction in gas phases, chemical vapor deposition of novel nanosized materials (organosilicon, organotin, organoselenium, organogermanium and organothiene materials.) at the Laboratory of Laser Chemistry, Institute of Chemical Process Fundamentals, Czech Academy of Sciences. Between 2005 and 2009 she worked as Assistant Professor at the University of St Cyril and Methodius, Macedonia. Since beginning of 2009, Prof. Tomovska has joined POLYMAT institute, University of the Basque Country as Ikerbasque Researcher Professor. Her current research interest include (photo)polymerization in dispersed media and preparation of new waterborne polymer and composite materials for application in waterborne coatings and adhesives, and synthesis of nanostructured materials for application in CO2 capture and conversion, gas sensors, SERS, etc. She has published more than 70 papers and 7 chapter of books.

Reference

Pérez-Martínez, B., Aboudzadeh, M., Schubert, U., Leiza, J., & Tomovska, R. (2020). Microwave irradiation versus conventional heating assisted free-radical copolymerization in solutionChemical Engineering Journal, 399, 125761.

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