Although radical polymerization is used in the synthesis of about half the world’s polymers, details of exactly what is going on in the reaction soup in complex industrial settings have been sketchy at best. As the materials enter our lives as, for example, drugs, coatings, fibers and solar cells, controlling their reactions and therefore their properties is extremely important.
Scientists in New Zealand have recently addressed a fundamental part of this story by considering termination rate coefficients for a couple of very common reactions, using results from new analytical techniques to revisit our old understanding. They found the way the small polymers (oligomers) in the system move and their speed, i.e., their diffusion behavior, to be the critical factor. This work is published in a special issue of Macromolecular Chemistry and Physics, devoted to radical polymerization.
The people responsible, Greg Russell and his colleagues at the University of Canterbury, are experts in polymer kinetics. Russell explains, “The majority of chemists simply try to bring about reactions by mixing different chemicals together under different conditions. However it is also important, especially for those who make chemical products on a large scale, to have precise quantitative descriptions of the speeds at which reactions occur. Chemical kinetics is the field of work that develops such descriptions. It is therefore an area where chemistry and mathematics intersect.”
He goes on to say, “Arguably the hardest nut to crack in the radical polymerization scheme has been the termination reaction. In layman's terms, termination is the fundamental reaction whereby a polymer molecule stops growing larger. A reasonable analogy is human death, the process which ceases human life and thus prevents a human's age from mounting and mounting. In radical polymerization this reaction is diffusion controlled in rate, which means that its speed is determined by how fast the molecules move.” This speed of movement can depend on many factors such as how long the molecule is, the number of obstacles around the polymer, the temperature of the system, and so on. “This is the origin of the complexity of the termination reaction, and is the reason why, after over 60 years of intensive study, it is still not fully understood, not nearly.”
In this work Russell revisited some of the earliest questions about termination. “Recent years have seen the development of highly specialized techniques for measuring termination rate coefficients under precisely controlled conditions. I have taken this information and attempted to see whether it is consistent with systems where many different termination reactions occur at once, as is the case in commercial processes. For the monomer styrene I find there is consistency, but for methyl methacrylate there is not.”
In trying to explain this result, he eliminated most of the conventional views, and came to the conclusion that the answer lies with the oligomers in each system, which seem to have slightly different diffusional behavior.
Philipp Vana works at the University of Göttingen, where Greg Russell is currently on sabbatical. He specializes in radical polymerization and serves on the Advisory Board of Macromolecular Chemistry and Physics. He is the Guest Editor of the special issue. In his view, “Russell’s paper is especially exciting, as it demonstrates that the information gathered by modern and advanced methods is useful to reevaluate the results obtained by older methods. Completely new insights can be extracted by such an approach.” He adds that Russell’s work not only adds new information to the field, but also presents a nice view of the complete picture, “which helps us to understand the complete history of science instead of getting a short snapshot of the present.”
This historical perspective of the field is especially pertinent as the special issue focused on the kinetics and mechanism of radical polymerization was prepared in order to honor Michael Buback, who turns 65 this year and who, according to the editor Vana, “undisputably is one of the doyens in this field.” Recent years have seen the invention of new controlled polymerization methods and Vana says it is of “vital importance to fundamentally understand these new techniques in order to exploit their full potential for material design. The newly invented polymerization technologies also provided new avenues for unlocking the secrets of the conventional processes. Many important questions could be answered recently and it seems to be justified to resumé at this stage and to identify, which major questions need further attention.”
D. R. Tayler, K. Y. van Berkel, M. M. Alghamdi, G. T. Russell, “Termination Rate Coefficients for Radical Homopolymerization of Methyl Methacrylate and Styrene at Low Conversion,” Macromol. Chem. Phys. 2010, DOI: 10:1002/macp.200900668
Contact details:Prof. Greg Russell
If you need further information or are interested in a pdf of the original articles please contact me at email@example.com
New type of photosynthesis discovered
17.06.2018 | Imperial College London
New ID pictures of conducting polymers discover a surprise ABBA fan
17.06.2018 | University of Warwick
Moving into its fourth decade, AchemAsia is setting out for new horizons: The International Expo and Innovation Forum for Sustainable Chemical Production will take place from 21-23 May 2019 in Shanghai, China. With an updated event profile, the eleventh edition focusses on topics that are especially relevant for the Chinese process industry, putting a strong emphasis on sustainability and innovation.
Founded in 1989 as a spin-off of ACHEMA to cater to the needs of China’s then developing industry, AchemAsia has since grown into a platform where the latest...
The BMBF-funded OWICELLS project was successfully completed with a final presentation at the BMW plant in Munich. The presentation demonstrated a Li-Fi communication with a mobile robot, while the robot carried out usual production processes (welding, moving and testing parts) in a 5x5m² production cell. The robust, optical wireless transmission is based on spatial diversity; in other words, data is sent and received simultaneously by several LEDs and several photodiodes. The system can transmit data at more than 100 Mbit/s and five milliseconds latency.
Modern production technologies in the automobile industry must become more flexible in order to fulfil individual customer requirements.
An international team of scientists has discovered a new way to transfer image information through multimodal fibers with almost no distortion - even if the fiber is bent. The results of the study, to which scientist from the Leibniz-Institute of Photonic Technology Jena (Leibniz IPHT) contributed, were published on 6thJune in the highly-cited journal Physical Review Letters.
Endoscopes allow doctors to see into a patient’s body like through a keyhole. Typically, the images are transmitted via a bundle of several hundreds of optical...
Light detection and control lies at the heart of many modern device applications, such as smartphone cameras. Using graphene as a light-sensitive material for...
Water molecules exist in two different forms with almost identical physical properties. For the first time, researchers have succeeded in separating the two forms to show that they can exhibit different chemical reactivities. These results were reported by researchers from the University of Basel and their colleagues in Hamburg in the scientific journal Nature Communications.
From a chemical perspective, water is a molecule in which a single oxygen atom is linked to two hydrogen atoms. It is less well known that water exists in two...
13.06.2018 | Event News
08.06.2018 | Event News
05.06.2018 | Event News
15.06.2018 | Materials Sciences
15.06.2018 | Ecology, The Environment and Conservation
15.06.2018 | Power and Electrical Engineering