Polymer Chemistry Blog

Santra et al. use recycled plastic-waste derived monomers to synthesize a redox-responsive self-immolative amphiphilic polyurethane nanoassembly.

Polymeric nanoparticles have undeniably found numerous applications in fields ranging from medicine to nanoelectronics. Despite the significant progress in the area, there is an increasing demand in chemotherapeutics to construct polymeric nanoassemblies able to encapsulate and deliver cargo on-demand. Most polymeric nanocarriers suffer from uncontrolled disassembly leading to premature, non-specific guest release while often; guests need to be covalently entrapped to achieve high encapsulation stability.

To address these issues, Molla and collaborators developed a strategy that allows upcycling plastic waste to synthesize a redox-responsive, self-immolative amphiphilic polyurethane that assembles into robust, tightly packed nanoassemblies with high encapsulation efficiency and stability. More specifically the upcycled-plastic nanocontainers were equipped with aromatic moieties enhancing their stability, disulfide bonds offering redox response and tertiary amines inducing charge tunability. Triethylene glycol monomethyl ether units were periodically incorporated on the polymer to enhance hydrophilic interactions with water. Computational studies supported that the high encapsulation stability observed in these polyurethane nanocarriers stems from supramolecular cross-linking via π–π stacking and H-bonding interactions. Notably, in a redox environment 70 % of guest release was obtained from the self-immolative polyurethane nanocarriers while significantly reduced release was observed in polymers lacking the disulfide linker and polymers lacking the aromatic component.  The high encapsulation stability was supported by the low leakage coefficient measured in FRET experiments. Pleasingly, zeta potential measurements revealed the generation of nanoassemblies with positive surface charge at a tumor extracellular matrix relevant pH was attributed to the tertiary amine component.

In summary, a plastic waste derived monomer was used as a basis to create robust self-immolative polyurethane nanocarriers with promising biomaterial characteristics such as biocompatibility, triggered release, and environment-specific charge modulation.

Mijanur Rahaman Molla et al., Supramolecularly cross-linked nanoassemblies of self-immolative polyurethane from recycled plastic waste: high encapsulation stability and the triggered release of guest molecules, Polym. Chem., 2022, 13, 3294-3303.

Link to the paper: https://pubs.rsc.org/en/content/articlelanding/2022/PY/D2PY00341D

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

Harrier et al. highlight the encapsulation methodology as a readily available, efficient methodology to perform ROPs in aqueous dispersions.

Ring opening polymerizations (ROP) are widely used to synthesize a variety of biodegradable polymers typically under the strict limitations requiring anhydrous media and inert atmosphere (usually dictating the use of complex setups such as Schlenk lines or glove boxes). These practical limitations limit the polymeric material accessible by ROP.
To address this limitation, Guironnet and collaborators implemented a droplet microfluidic encapsulation strategy and systematically investigated both the process and the formulation parameters that govern the stability of the formed micro-droplets. The identification of these parameters together with the addition of amphiphilic block copolymers (PEG-PVL, PEG-PCL, and Pluronic) and a hydrophobe (hexadecane) allowed to control the viscosity, surface tension, and hydrophobicity of the formed droplets. As a result, the conditions in which the ROP catalyst was efficiently shielded in the aqueous dispersion could be identified and used to achieve higher monomer conversion and higher molecular weight polymers in the polymerization of valerolactone and caprolactone. By changing the amphiphilic block copolymer composition, ROP reaction time could also be further improved. To highlight the strength of this approach, these design rules were also used to tune the viscosity and surface tension of the droplets during ROP of propylene oxide catalyzed by an organic Lewis-Pair catalyst system (i.e. a phosphazene base and triethyl borane), leading to the synthesis of polyether particles dispersed in water.

In summary this study highlights the power and versatility of the encapsulation methodology applied with an off-the-shelf droplet-based microfluidic device and establish the fundamental guiding principles to encapsulate water-sensitive polymerization catalysts to efficiently synthesize spherical polymer particles dispersed in water.

Design rules for performing water-sensitive ring-opening polymerizations in an aqueous dispersion, Polym. Chem., 2022, 13, 2459-2468

Link to the paper: https://pubs.rsc.org/en/content/articlelanding/2022/py/d2py00069e#cit11

Dr. Kelly Velonia is an Advisory Board Member and a Web Writer for Polymer Chemistry. She joined the Department of Materials Science and Technology in 2007. Research in her group focuses on the synthesis and applications of bioconjugates and biopolymers.

An international group of polymer scientists from the International Union of Pure and Applied Chemistry (IUPAC) Subcommittee on Polymer Terminology (SPT) convey concerns with the basic terms typically used for classifying methods of polymer synthesis and initiate a dialogue with the broader polymer community to resolve terminology shortcomings.

In 1994 the IUPAC SPT highlighted long-standing problems with the widely used terms “step-growth polymerization” and “chain-growth polymerization,” which describe two discrete mechanisms of polymer growth, and depreciated their use since they do not describe the fundamental differences in the growth of polymers by these methods and are often confusing. To address this, the 1994 SPT members recommended the terms polycondensation and polyaddition for the two variants of “step-growth polymerization”, and similarly chain polymerization and condensative chain polymerization for the two variants of “chain-growth polymerization”. However, these terms have not been widely adopted by the community, and have also created confusion.

In this contribution, current IUPAC SPT members provide detailed descriptions of these two processes and outline concerns associated with the terms “step-growth,” “chain-growth,” and related terms. By discussing in detail the historical development of these terms and analyzing their use in current textbooks, the authors underline the lack of consensus in the terminology used within the polymer community. Interestingly, they demonstrate how the similarity of these terms leads to further confusion when translating into languages other than English. Finally, examples of polymerizations that cannot be classified under the umbrella of the existing definitions and have no designated terminology are discussed.

In 2019, IUPAC recognized the need to resolve these polymer terminology shortcomings and approved a project aimed to propose new terminologies. The authors, as members of the IUPAC SPT task group studying this issue, aim to clarify the naming of polymerisation processes and invite all members of the community to contribute by emailing to polymer.terminology@iupac.org.

Tips/comments directly from the authors:

• We, the subcommittee of polymer nomenclature (SPT), want to raise attention to a long-standing dilemma in the terms that many of us use every day: “step-growth” and “chain-growth” polymerization.
• A number of terms have been used over the past century to describe these two fundamental mechanisms of polymer growth, and many prominent polymer chemists have noted their shortcomings in textbooks.
• We detail here the history of the terms, current usage in textbooks, and our specific concerns.
• In particular, we invite feedback from the broader polymer community, including from students, lecturers, researchers, and anyone who uses polymer science regularly.

Reconsidering terms for mechanisms of polymer growth: the “step-growth” and “chain-growth” dilemma, Polym. Chem., 2022, 13, 2262-2270.

Link to the paper: https://pubs.rsc.org/en/content/articlelanding/2022/py/d2py00086e

You can follow the authors on twitter: @IUPACPolymer

Dr. Kelly Velonia is an Advisory Board Member and a Web Writer for Polymer Chemistry. She joined the Department of Materials Science and Technology in 2007. Research in her group focuses on the synthesis and applications of bioconjugates and biopolymers.