Overcoming Barriers in Polycarbonate Synthesis: A Streamlined Approach for the Synthesis of Cyclic Carbonate Monomers

Hemiacetal Ester Side Chains as a Mild Protecting Group for Carboxylic Acids in Polycarbonate Backbones

Hemiacetal esters are versatile functional groups known for their unique ability to degrade under mild conditions such as exposure to water, alcohols, organic acids, or heat. In this study, hemiacetal esters are introduced as mild, transient protecting groups for carboxylic acids along polycarbonate backbones. A six-membered cyclic carbonate monomer is synthesized by reacting ethyl vinyl ether with a carboxylic acid precursor, demonstrating high efficiency and stability under nucleophilic polymerization conditions. Potential susceptibilities of the hemiacetal esters to transacetalization reactions do not occur under these polymerization conditions. Instead, well-defined homo and PEG-based block copolymers are obtained with narrow molecular weight distributions and preserved hemiacetal ester functionalities. These labile side chain groups enabled facile deprotection, yielding polycarbonates with free carboxylic acids, holding significant potential for applications in drug delivery, sustainable polymers, and advanced functional materials.

3D Printing with tuneable degradation: Thiol-ene and thiol-yne containing formulations for biomedical applications

Despite advances in the range of materials that can be used in 3D printing and their applications across numerous scientific disciplines, the controlled breakdown of their solid structures after printing remains challenging. In this study we report the development of tuneable degradable 3D printed formulations, that could be 3D printed using standard digital light processing (DLP) and then degraded as required under mild conditions. Thirteen thiol-ene and thiol-yne formulations were designed to provide a range of tailored mechanical properties, with controlled degradation rates, and specific thermal behaviours with potential relevance to biomedical applications. The formulations ranged from ones with high stiffness for structural applications, through to those capable of rapid degradation. These formulations demonstrate full degradability and stability in physiological conditions, showing potential for future drug delivery applications pending further toxicity and release studies. This balance of degradability and mechanical robustness offers significant potential for enhancing patient safety and reducing the invasiveness of surgical treatments as directed by clinical needs.

Degradable Ureido-Polycarbonate Block Copolymers with a Complex UCST Thermoresponse

In this work, amphiphilic block copolymers (BCs) consisting of a hydrophilic poly(ethylene glycol) methyl ether (PEG) and a degradable polycarbonate block derived from 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) with pendant ureido units, along with corresponding homopolycarbonates are described. Polymers are synthesized by combining ring opening polymerization (ROP) and thiol-ene/yne functionalization to incorporate UCST-promoting ureido groups. For homopolycarbonates, increasing the ureido groups density along the polymer chain facilitates the upper critical solution temperature (UCST)-type thermoresponse in water. Because of their amphiphilic character, BCs form stable self-assemblies either by direct dispersion in water, co-solvent method or microfluidics. Upon heating, these self-assemblies swell, and collapse due to extensive hydration of the polycarbonate block, rather than becoming solubilized. Thermoresponsiveness is analyzed in terms of the number of ureido groups in the polycarbonate for a given polycarbonate block length as well as the length of polycarbonate block. As a proof of concept, the potential of these self-assemblies as thermoresponsive drug nanocarriers is evaluated, using curcumin as a hydrophobic model drug.

Aliphatic polycarbonates with acid degradable ketal side groups as multi-pH-responsive immunodrug nanocarriers

Pharmacokinetics and biodistribution profiles of active substances are crucial aspects for their safe and successful administration. Since many immunogenic compounds do not meet all requirements for safe and effective administration, well-defined drug nanocarrier systems are necessary with a stimuli-responsive drug-release profile. For this purpose, a novel pH-responsive aliphatic cyclic carbonate is introduced with benzyl ketal side chains and polymerized onto a poly(ethylene glycol) macroinitiator. The resulting block copolymers could be formulated via a solvent-evaporation method into well-defined polymeric micelles. The hydrophobic carbonate block was equipped with an acid degradable ketal side group that served as an acid-responsive functional group. Already subtle pH alternations led to micelle disassembly and the release of the active cargo. Furthermore, basic carbonate backbone degradation assured the pH responsiveness of the nanocarriers in both acidic and basic conditions. To investigate the delivery capacity of polymeric micelles, the model small molecule compound CL075, which serves as an immunotherapeutic TLR7/8 agonist, was encapsulated. Incubation studies with human blood plasma revealed the absence of undesirable protein adsorption on the drug-loaded nanoparticles. Furthermore, in vitro applications confirmed cell uptake of the nanodrug formulations by macrophages and the induction of payload-mediated immune stimulation. Altogether, these results underline the huge potential of the developed multi-pH-responsive polymeric nanocarrier for immunodrug delivery.

Introducing SuFEx click chemistry into aliphatic polycarbonates: a novel toolbox/platform for post-modification as biomaterials

As a biodegradable and biocompatible biomaterial, aliphatic polycarbonates (APCs) have attracted substantial attention in terms of post-polymerization modification (PPM) for functionalization. A strategy for the introduction of sulfur(VI)-fluoride exchange (SuFEx) click chemistry into APCs for PPM is proposed for the first time in this work. 4'-(Fluorosulfonyl)benzyl 5-methyl-2-oxo-1,3-dioxane-5-carboxylate (FMC) was designed as a SuFEx clickable cyclic carbonate for APCs via ring-opening polymerization (ROP), and an operational and nontoxic synthetic route was achieved. FMC managed to undergo both ROP and PPM through the SuFEx click chemistry organocatalytically without constraining or antagonizing each other, using 1,5,7-triazabicyclo[4,4,0]dec-5-ene (TBD) as a co-organocatalyst here. Its ROP was systematically investigated, and density functional theory (DFT) calculations were performed to understand the acid-base catalytic mechanism in the anionic ROP. Exploratory investigations into PPM by SuFEx of poly(FMC) were conducted as biomaterials, and the one-pot strategies to achieve both ROP and SuFEx were confirmed.

Effects of Hydrophobicity on Antimicrobial Activity, Selectivity, and Functional Mechanism of Guanidinium-Functionalized Polymers

In this study, a series of guanidinium-functionalized polycarbonate random co-polymers is prepared from organocatalytic ring-opening polymerization to investigate the effect of the hydrophobic side chain (ethyl, propyl, isopropyl, benzyl, and hexyl) on their antimicrobial activity and selectivity. Although the polymers exhibit similar minimum inhibitory concentrations, the more hydrophobic polymers exhibit a faster rate of bacteria elimination. At higher percentage content (20 mol%), polymers with more hydrophobic side chains suffer from poor selectivity due to their high hemolytic activity. The highly hydrophobic co-polymer, containing the hydrophobic hexyl-functionalized cyclic carbonate, kills bacteria via a membrane-disruptive mechanism. Micelle formation leads to a lower extent of membrane disruption. This study unravels the effects of hydrophobic side chains on the activities of the polymers and their killing mechanism, providing insights into the design of new antimicrobial polymers.

Simple and Efficient Synthesis of Functionalized Cyclic Carbonate Monomers Using Carbon Dioxide

Aliphatic polycarbonates represent an important class of materials with diverse applications ranging from battery electrolytes, polyurethane intermediates, and materials for biomedical applications. These materials can be produced via the ring-opening polymerization (ROP) of six- to eight-membered cyclic carbonates derived from precursor 1,3- and 1,5-diols. These diols can contain a range of functional groups depending on the desired thermal, mechanical, and solution properties. Generally, the ring closure to form the cyclic carbonate requires the use of undesirable and hazardous reagents. Advances in synthetic methodologies and catalysis have enabled the use of carbon dioxide (CO₂) to perform these transformations with a high conversion of diol to cyclic carbonate, yet modest isolated yields due to oligomerization side reactions. In this Letter, we evaluate a series of bases in the presence of p-toluenesulfonyl chloride and the appropriate diol to better understand their effect on the yield and presence of oligomer byproducts during cyclic carbonate formation from CO₂. From this study, N,N-tetramethylethylenediamine (TMEDA) was identified as an optimal base, facilitating the preparation of a diverse array of both six- and eight-membered carbonates from CO₂ within 10 to 15 min. The robust conditions for both, the preparation of the diol precursor, and the TMEDA-mediated carbonate synthesis enabled readily telescoping the two-step reaction sequence, greatly simplifying the process of monomer preparation.

Organic carboxylate salt-enabled alternative synthetic routes for bio-functional cyclic carbonates and aliphatic polycarbonates

A cyclic carbonate with an ammonium carboxylate residue was found to serve as a nucleophile for esterification with alkyl bromides via the SN2 mechanism.

Broad-Spectrum Antiviral Peptides and Polymers

As the human cost of the pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is still being witnessed worldwide, the development of broad-spectrum antiviral agents against emerging and re-emerging viruses is seen as a necessity to hamper the spread of infections. Various targets during the viral life-cycle can be considered to inhibit viral infection, from viral attachment to viral fusion or replication. Macromolecules represent a particularly attractive class of therapeutics due to their multivalency and versatility. Although several antiviral macromolecules hold great promise in clinical applications, the emergence of resistance after prolonged exposure urges the need for improved solutions. In the present article, the recent advancement in the discovery of antiviral peptides and polymers with diverse structural features and antiviral mechanisms is reviewed. Future perspectives, such as, the development of virucidal peptides/polymers and their coatings against SARS-CoV-2 infection, standardization of antiviral testing protocols, and use of artificial intelligence or machine learning as a tool to accelerate the discovery of antiviral macromolecules, are discussed.