Polymer Chemistry Blog

Abad et al. develop formulations of self-assemblies containing nucleobase analogues via seeded RAFT in water.

Polymer chemists have long exploited the specific hydrogen bonding interactions between nucleobase pairs to control polymer structure or sequence, to template polymerizations or drive self-assembly. Although several approaches have been employed for the synthesis of nucleobase containing polymers, the poor solubility of nucleobase-containing monomers has hampered their polymerization in water.

To address this, Blasco, Piñol and collaborators synthesized a diblock copolymer containing poly(ethylene glycol) (PEG) and 2,6-diacylaminopyridine (DAP)  polymethacrylate via RAFT. Upon dispersing in water this macro-CTA agent was used for the aqueous seeded RAFT polymerization of 2-hydroxypropyl methacrylate (HPMA). Furthermore, a phase diagram that correlates the degree of polymerization and solid concentration with the morphologies of the resulting self-assemblies was constructed. Through this systematic study, low to high order morphologies (from spherical micelles to worms and to vesicles) could be observed. Interestingly all morphologies proved to be stable for extended periods of time with the exception of worms found to turn into spherical micelles after few weeks. To exploit the ability to functionalize the DAP moieties through H-bonding during aqueous seeded RAFT polymerization, a cross-linker bearing four thymine terminal groups was used. Finally, the higher stability of the assemblies produced via supramolecular cross-linking was studied via encapsulation and subsequent release of the hydrophobic probe Nile Red.

In summary, this study provides a metal-free methodology to produce self-assemblies containing nucleobase analogues in high concentrations via aqueous seeded RAFT polymerization.  The ability to control assembly, functionalize via exploiting supramolecular interactions and load with cargo, enhances their potential use as nanocarriers.

Tips/comments directly from the authors:

• This new strategy integrating non-water soluble groups, such as DAP units, into a BC enabled the preparation of highly concentrated aqueous self-assembly dispersions using the PISA methodology.
• The DAP units were further exploited for supramolecular H-bonding functionalization with cross-linker containing complementary thymine groups.
• Previous work on amphiphilic block copolymers having DAP units has proved their potential to prepare stimuli-responsive self-assemblies of interest in nanomedicine by nanoprecipitation or microfluidic. This article takes an important step forward since the potential of the polymers is upgraded with the processing of highly concentrated dispersions by this new straightforward strategy.
• This paper is the result of a collaborative effort between the groups at University of Zaragoza (Spain) and Heidelberg University (Germany)

Citation of the paper: Aqueous seeded RAFT polymerization for the preparation of self-assemblies containing nucleobase analogues, Polym. Chem., 2023,14, 71-80.

Link to the paper: https://pubs.rsc.org/en/content/articlelanding/2023/py/d2py01250b

Link to authors website (or social media)

https://liquidcrystals.unizar.es/  @clip_group_lab (Twitter)

https://www.imseam.uni-heidelberg.de/blasco @EvaBlascoPo (Twitter)

Dr. Kelly Velonia is an Advisory Board Member and a Web Writer for Polymer Chemistry. She joined the Department of Materials Science and Technology at the University of Crete in 2007. Research in her group focuses on the synthesis and applications of bioconjugates and biopolymers. You can follow Kelly on twitter @KellyVelonia.

Johnson et al. propose that a synergy between chemical sciences and law research needs to be deployed to address the plastic pollution challenge through tracing technologies.

Among the major challenges faced by societies worldwide is the reduction of plastic pollution which has risen to be one of the largest environmental issues of the planet. A key barrier to improving plastic management is the inability to trace plastics along supply and value chains.

Addressing this issue, Johnson, Barner-Kowollik and colleagues with equal first authors Chambers and Holloway highlight how valorization of state-of-the-art chemistry could help eradicate plastic anonymity and propose that plastic management can become efficient once production of traceable plastics is implemented and incorporated into the legal frameworks for plastics governance.

To embed information into plastics and access it throughout its lifetime, both the inherent chemical composition of the macromolecules and chemical labelling can be exploited. Spectroscopic identification can fingerprint polymer chemistry but tracing a specific polymer to the producer would require introducing unique labels in the plastic material, with little information depth. Alternatively, information can be introduced through physically labelling the surface of a material. Both approaches carry information that can be readily affected by degradation over time. Chemical labeling with sequence-defined polymers on the other hand can be used to embed all necessary information within the material without being compromised by degradation. Barner-Kowollik and coworkers highlight state-of-the-art synthetic routes toward sequence-defined polymers, review the approaches to decode them and provide a set of criteria to be fulfilled by advanced read-out methodologies in order to successfully integrate such advanced plastics into recycling facilities.

Critical improvements to regulation policies need to be implemented to leverage on advanced plastics and especially sequence-defined polymers traceability. The authors propose that five key areas need to be addressed in law and policy: design or eco-design standards to reduce the environmental impacts of products and services along their entire lifecycle, consumer behavior to reduce consumption and encourage eco-friendlier choices, recycling systems to compensate the high cost of collecting, sorting and recycling materials, extended-producer responsibility schemes to respond to plastic waste, and combatting illegal waste streams that breache domestic or international laws.

This perspective is a critical overview on how chemistry, law and social sciences should advance, coordinate and collaborate in order to address the issue of plastic pollution in the most efficient manner.

Tips/comments directly from the authors:

1. It’s been an amazing journey for our team of chemists to work with colleagues from the faculty of law. It took many conversations, lots of explanations and the willingness on both sides to learn about law and chemistry, respectively. The process was enormously rewarding for the entire team, who continues to work together on developing plastic tracers in a joint effort between law and chemistry.
2. We highly recommend to all chemistry colleagues to research out into the humanities and social sciences for collaboration opportunities. These research fields have equal importance to the natural sciences and engineering, deliver enormous value and help chemists to put an entirely different perspective onto their own research. We believe the chemistry community should be at the absolute forefront of engaging with the social sciences and humanities.
3. We are very proud of Polymer Chemistry (RSC) for opening the journal to law research that speaks to chemical problems and being a trailblazer for true transdisciplinary research.

Citation to the paper: Using precision polymer chemistry for plastics traceability and governance, Polym. Chem., 2022, 13, 6082-6090.

Link to the paper: https://pubs.rsc.org/en/content/articlelanding/2022/py/d2py01180h

Follow Christopher Barner-Kowollik on Twitter @BarnerKowollik and the QUT Centre for Materials Science @QUTmaterials to keep up to date with their latest research

Dr. Kelly Velonia is an Advisory Board Member and a Web Writer for Polymer Chemistry. She joined the Department of Materials Science and Technology at the University of Crete in 2007. Research in her group focuses on the synthesis and applications of bioconjugates and biopolymersYou can follow Kelly on twitter @KellyVelonia