Polymers are natural or synthetic substances composed of large molecules made up of multiples of atoms or simpler molecules called monomers. In the lab, some polymers can be made by merely adding one monomer to another in a chain, such as in polymers found in plastic products like polyethylene.
The specific type of polymers developed by Madrid, Arco and Perez, on the other hand, are called 鈥渟timuli-responsive鈥� or smart polymers, since they undergo significant changes in response to small stimuli like temperature, pH levels, light, and other variables. Such polymers can be used to deliver drugs like insulin to their target organs, or as scaffolds for oral tissue regeneration, depending on their characteristics.聽
To synthesize such polymers, the team used a method called Reversible Addition Fragmentation Chain Transfer (RAFT) polymerization. While there are other ways to synthesize smart polymers in the lab, it can be hard to control how their monomers connect with one another using these more conventional methods. This results in polymer chains of various lengths and a broad molecular weight distribution. RAFT polymerization helps limit the distribution size, making the design and traits of the polymers easier to tailor.
鈥淩AFT polymerization helps control the growth of polymer chains by mitigating the formation of chains that can no longer grow (a.k.a. 鈥榙ead鈥� polymers),鈥� said Madrid in an interview with the UPD College of Science Media Team, 鈥渢hereby creating a narrower molecular weight distribution which can allow more tailored polymer designs or properties.鈥�
With this method, the team successfully synthesized heat responsive polymers using two monomers: di(ethylene glycol) methyl ether methacrylate (DEGMEMA) and methyl methacrylate (MMA). In addition to being heat-responsive, the polymers were also tested to be biocompatible, meaning they can interact with systems like human bodies without any adverse effects.
The study of Madrid, Arco and Perez was also the first to synthesize polymers from DEGMEMA and MMA via RAFT copolymerization using an ionic liquid, [HPY][PF6], as a solvent. This is important because, as the team says, polymerization in organic solvents raises many environmental concerns due to their being flammable and unstable, and having the tendency to release harmful compounds into the environment.聽
Using ionic solvents like [HPY][PF6] is a comparatively 鈥済reener鈥� solution, in addition to being quicker and having better polymerization kinetics.
The team鈥檚 breakthrough opens doors to exciting new directions in polymer research using different monomers and solvents. 鈥淭he results open up the potential for using other hexylpyridinium ionic liquids to create dual-responsive polymers (e.g. responsive to both temperature and pH), which are valuable for biomedical applications such as drug delivery,鈥� Madrid said.聽聽
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