Scientists from Tokyo Tech have discovered that utilizing scanning ultraviolet (UV) light through a slit can enhance the efficiency of photopolymerization reactions, resulting in polymers with greater molecular weight. This simple yet effective method encourages molecular diffusion among the reactants, which leads to the creation of longer polymer chains while significantly reducing energy consumption. This breakthrough paves the way for more sustainable and efficient methods of polymer synthesis.
Researchers from Tokyo Tech have revealed that by scanning ultraviolet (UV) light through a slit, the efficiency of photopolymerization reactions can be significantly enhanced, leading to the production of polymers with greater molecular weight. This uncomplicated approach promotes molecular diffusion in the reactants, which favors the development of longer polymer chains and simultaneously conserves substantial amounts of energy, opening doors for more sustainable and efficient polymer synthesis.
Polymers are materials constructed from long, repeated chains of molecules, and the way these chains interact is what primarily determines the physical and chemical properties of a polymer. Following a fundamental understanding of polymers that dates back to the 1930s, external forces acting upon them have generally been seen as harmful. For instance, when a polymer is stretched, it can become tangled or even break apart, reducing its overall strength.
However, in recent decades, researchers have consistently shown that external forces can also yield beneficial effects on polymers. When applied correctly, mechanical forces and flow fields can introduce new functionalities to specific polymers by changing their phase, optical properties, and crystallinity. Despite significant advancements in this area—termed mechanochemistry—there remains limited knowledge about how these forces can influence the growth characteristics of polymers.
Fortunately, a team of researchers led by Professor Atsushi Shishido at the Tokyo Institute of Technology set out to explore this subject further. Their study, published in Macromolecules on July 29, 2024, examined how dynamic UV lighting creates flow fields that affect the photopolymerization process, presenting an intriguing and flexible method to control polymer synthesis.
The specific photopolymerization reaction analyzed involved M6BACP as the monomer (the essential component for the final polymer) along with Irgacure 651, a photoinitiator. This compound absorbs UV light and breaks down into reactive free radicals that engage with the monomers, prompting them to bond. Unlike conventional photopolymerization processes, which uniformly expose the entire solution to UV light, this research utilized a slowly moving slit to shine the UV light.
This straightforward approach led to significant differences in the resulting polymers, as showcased in various comparative experiments. “Using scanning UV light for photopolymerization resulted in high molecular weight polymers, with a reduction of 90% in the required exposure dose compared to using static uniform light,” emphasizes Shishido.
The researchers theorized that the UV light generates molecular flows resulting in two key effects. Firstly, it causes the growing polymers to slightly diffuse toward areas that haven’t been exposed to light, where their concentration is lower. This enables continued growth as new radicals become available. Secondly, both the radicals and monomers diffuse as well; radicals are directed to the unirradiated zones, and monomers towards the irradiated ones. This combined diffusion leads to a lower concentration of radicals relative to monomers in the exposed areas, decreasing the likelihood of termination reactions that could limit the growth of polymer chains.
This study not only enhances the understanding of photopolymerization reactions but also demonstrates an effective way to elevate existing industrial processes and polymer materials. “The method developed considerably enhances polymerization efficiency by simply adding movement to the irradiation light, without necessitating changes to the compounds or reaction systems currently in use. This can lower the energy costs of photopolymerization, which is integral to various industrial applications, and it is anticipated to be applied in manufacturing processes and foundational technologies for polymer synthesis,” explains Shishido. Notably, the benefits observed extended beyond M6BACP to include a variety of common polymers, such as acrylates.
