We all know how versatile plastics are, they have a great variety of uses, the problem with this material is precisely its resistance, since they are difficult to degrade making them persist in the environment for a long time, on the other hand, there is a great interest in the development of new biodegradable polymers for use in the field of biomedicine, these aspects have driven the interest in developing polymers of hydrolytic degradation, that is to say, that decompose easily in water.
Until now, it has been difficult to develop a polymer that degrades in water. Source: Wikimedia.org.
Vinyl polymers, those that we commonly call plastics, are polymers that are obtained by assembling a large number of vinyl monomers, that is, molecules that contain a carbon-carbon double bond, the simplest vinyl polymer of all being polyethylene, in which the monomer is the ethylene molecule; and when these molecules are joined together, that is, polymerized, they are joined by their double bonds forming long chains of thousands of carbon atoms.
Polyethylene is the simplest vinyl polymer. Source: image prepared in powerpoint.
This type of polymer has been the subject of much research mainly because of its ease of synthesis, which has made it possible to manufacture various functional materials with well-defined structures. However, despite having been the subject of intense research, no viable ways have been found to increase its low hydrolytic degradation, and it cannot compete with aliphatic polyesters, whose presence of ester groups confers them greater degradation. This limits the use of vinyl polymers in the field of biomedicine, where they are of great interest due to the ease of functionalizing them and adjusting their structure; not to mention that they are also responsible for major environmental problems.
But thanks to a new technique for polymerizing vinyl polymers, macromolecules could be designed with a controlled and homogeneous structure that is also easily degradable. A CNRS research team at the Galien Paris-Saclay Institute succeeded in developing a copolymerization system in which they insert a cyclic acetal monomer into acrylamide, a polymer that has many industrial applications, to obtain polymers that are compatible with faster hydrolytic degradation, and which also, depending on the nature of the polymer, can adjust solubility as a function of temperature, which is highly desirable for the release of drugs in the body.
So far, degradable vinyl polymers have been approached by introducing an ester group into the polymer structure, using a method known as ring-opening radical polymerization (rROP) of cyclic ketene acetals (CKA), a process in which basically a cyclic monomer is converted into a polymer containing no rings, those rings are opened and extended along a polymer chain. And although many studies have been carried out with promising results, even the poor degradation of these polymers under physiological conditions remains a major limitation.
But the study published in the journal Nature Communications the research team reported on the copolymerization system that has overcome the limitations associated with polymers obtained by the rROP method of cyclic ketene acetals, their method allowed the synthesis of vinylic copolymers with a well-defined structure that exhibited fast hydrolytic degradation and complete water solubility, even higher than that observed in the most popular polyesters, such as poly lactic-co-glycolic acid (PLGA) or even poly lactic acid (PLA).
The synthesized copolymers can be heat sensitive and are easily degraded by water. Source: image elaborated in powerpoint.
The design of the copolymerization system was based on a structural analogy with polyacrylamide-co-styrene copolymers in which styrene was replaced by cyclic ketene acetal (CKA) units containing aromatic rings, giving rise to the polyacrylamide-co-cyclic acetal (P(AAm-co-CKA)) system.
For the tests, the first copolymerizations were made with 2-methylene-4-phenyl-1,3-dioxolane (MPDL) due to its open radical structure very close to that of styrene, then the solubility of the different copolymers in water (10 mg mL-1) was checked by transmittance measurements performed between 5 and 50 °C, They also managed to demonstrate that by changing the nature of the cyclic ketene acetal, they were able to modify the solubility of the copolymers by tuning their critical solution temperatures to the temperature of the human body.
This development is very relevant, on the one hand, the research team aims at the elaboration of polymers that could be used to administer drugs, formulating these polymers as nanoparticles capable of solubilizing at body temperature, and on the other hand, this method should also allow the fabrication of polymers that can degrade more easily in the environment.
Thanks for coming by to read friends, I hope you liked the information. See you next time.
Amaury Bossion, Chen Zhu, Léa Guerassimoff, Julie Mougin et Julien Nicolas (2022). Vinyl Copolymers with Faster Hydrolytic Degradation than Aliphatic Polyesters and Tunable Upper Critical Solution Temperatures. Nature Communications, 13, 2873