Polyisobutylene-Based Helical Block Copolymers with pH-Responsive Cationic Side-Chain Amino Acid Moieties by Tandem Living Polymerizations

A chemically engineered water-soluble block copolymer for redox responsive SO2 release in antibacterial therapy

Sulfur dioxide (SO2) has emerged as a promising gasotransmitter for various therapeutic applications, including antibacterial activities. However, the potential of polymeric SO2 donors for antimicrobial activities remains largely unexplored. Herein, we report a water-soluble, redox-responsive, SO2-releasing amphiphilic block copolymer poly(polyethylene glycol methyl ether methacrylate) (PPEGMA)-b-poly(2-((2,4-dinitrophenyl)sulfonamido)ethyl methacrylate (PM)) (BCPx) to investigate their antibacterial properties. BCPx contains hydrophilic polyethylene glycol (PEG) pendants and a hydrophobic SO2-releasing PM block, facilitating the formation of self-assembled nanoparticles (BCPxNp) in an aqueous medium, studied by critical aggregation concentration (CAC) measurements, dynamic light scattering (DLS), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). BCPxNp exhibits sustained SO2 release up to 12 h in the presence of glutathione (GSH), with a yield of 30-80% of theoretical SO2 release. In vitro antibacterial studies unveil the outstanding antibacterial activity of BCP3Np against Gram-positive bacteria Bacillus subtilis, as evidenced by FESEM and live/dead cell fluorescence assay. We further elucidate the antibacterial mechanism through reactive oxygen species (ROS) generation studies. Overall, the polymer exhibits excellent biocompatibility at effective antimicrobial concentrations and provides insights into the design of a new class of SO2-releasing polymeric antibacterial agents.

Synthesis of Thermo-Responsive Monofunctionalized Diblock Copolymer Worms

Poly(glycerol monomethacrylate)-block-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) with worm-like morphology is a typical example of reversible addition-fragmentation chain transfer (RAFT) dispersion polymerized thermo-responsive copolymer via polymerization-induced self-assembly (PISA) in aqueous solution. Chain transfer agents (CTAs) are the key component in controlling RAFT, the structures of which determine the end functional groups of the polymer chain. It is therefore of interest to monofunctionalize the polymers via CTA moiety, for bioactive functionality conjugation and in the meantime maintain the precisely controlled morphology of the copolymers and the related property. In this work, a newly designed CTA 5-(2-(tert-butoxycarbonylamino) ethylamino)-2-cyano-5-oxopentan-2-yl benzodithioate (t-Boc CPDB) was synthesized and used for the RAFT polymerization of PGMA45-PHPMA120. Subsequently, PGMA45-PHPMA120 copolymers with primary amine, maleimide, and reduced L-glutathione (a tripeptide) monofunctionalized terminals were synthesized via deprotection and conjugation reactions. These monofunctionalized copolymers maintain worm-like morphology and thermo-responsive property in aqueous solution (10% w/v), as confirmed by the transmission electron microscopy (TEM) images, and the observation of the phase transition behavior in between 4 °C and room temperature (~20 °C), respectively. Summarily, a range of thermo-responsive monofunctionalized PGMA45-PHPMA120 diblock copolymer worms were successfully synthesized, which are expected to offer potential biomedical applications, such as in polymer therapeutics, drug delivery, and diagnostics.

Fatty Acid-Based Polymeric Micelles to Ameliorate Amyloidogenic Disorders

To develop anti-amyloidogenic inhibitors for ameliorating the treatment of diabetes, herein, we have synthesized amphiphilic block copolymers with side-chain fatty acid (FA) moieties via reversible addition fragmentation chain-transfer (RAFT) polymerization....

Block Copolymer Synthesis by the Combination of Living Cationic Polymerization and Other Polymerization Methods

The foremost limitation of block copolymer synthesis is to polymerize two or more different types of monomers with different reactivity profiles using a single polymerization technique. Controlled living polymerization techniques play a vital role in the preparation of wide range of block copolymers, thus are revolutionary techniques for polymer industry. Polymers with good control over molecular weight, molecular weight distribution, chain-end functionality and architectures can be prepared by these processes. In order to improve the existing applications and create new opportunities to design a new block copolymer system with improved physical and chemical properties, the combination of two different polymerization techniques have tremendous scope. Such kinds of macromolecules may be attended by combination of homopolymerization of different monomers by post-modification techniques using a macroinitiator or by using a dual initiator which allows the combination of two mechanistically distinct techniques. This review focuses on recent advances in synthesis of block copolymers by combination of living cationic polymerization with other polymerization techniques and click chemistry.

Amino acid-derived stimuli-responsive polymers and their applications

The recent advances achieved in the study of various stimuli-responsive polymers derived from natural amino acids have been reviewed.

Side-chain amino acid based cationic polymer induced actin polymerization

Actin filament dynamics is important for proper cellular functions and is controlled by hundreds of actin binding proteins inside the cells. There are several natural and synthetic compounds that are able to bind actin and alter the actin filament dynamics. Since the actin dynamics changes due to nonspecific electrostatic interactions between negatively charged actin and positively charged proteins, and natural or synthetic compounds, herein we report the synthesis of poly(tert-butyl carbamate (Boc)-l-alanine methacryloyloxyethyl ester) (P(Boc-Ala-HEMA)) homopolymer in a controlled fashion by the reversible addition-fragmentation chain transfer (RAFT) polymerization. Subsequent deprotection of the Boc groups in the homopolymer under acidic conditions resulted in a positively charged polymer with primary amine moieties at the side chains. This cationic polymer (P(NH₃ ⁺-Ala-HEMA)), is able to nucleate actin in vitro. The cationic polymer and corresponding partially fluorescence tagged polymer are able to nucleate actin filament in vivo. These polymers are nontoxic to the cultured cells and also stabilize the filamentous actin in vitro.

Stimuli responsive self-healing polymers: gels, elastomers and membranes

The development of responsive polymers with self-healing properties has expanded significantly which allow for the fabrication of complex materials in a highly controllable manner, for diverse uses in biomaterials science, electronics, sensors and actuators and coating technologies.

A nonconjugated macromolecular luminogen for speedy, selective and sensitive detection of picric acid in water

A conventional fluorophore-free water-soluble copolymer based on poly(styrene-alt-maleimide) has been found to be selective and sensitive detection of picric acid in a 100% aqueous environment with prompt response.

pH and Salt Effects on Surface Activity and Self-Assembly of Copolymers Containing a Weak Polybase

Copolymers with well-defined architectures, controlled molecular weights, and narrow molar mass dispersities (Đ) were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The resultant polymers contain different combinations of the pH-responsive monomer 2-(diethylaminoethyl) methacrylate (DEAEMA), the hydrophobic comonomer butyl methacrylate (BMA), and a neutral hydrophilic stabilizing monomer polyethylene glycol monomethyl ether methacrylate (designated O950). Surface tension and cryo-TEM measurements of native and heavy-atom stained samples were used to characterize the pH and salt responsiveness of the different polymers as a function of their composition. These studies indicate that while the polymers predominately self-assemble to form spherical micelles, a narrow size distribution is observed in aqueous solutions of poly(O950)-b-(BMA) and poly(O950)-b-(DEAEMA-co-BMA), whereas a broad size distribution characterizes the assemblies of poly(O950)-b-(DEAEMA) and poly(DEAEMA-co-BMA). In the latter case, micelles having diameters around 15-25 nm are found along with smaller aggregates (about 10 nm) mostly arranged in elongated necklace-like structures. The pH and salt-responsiveness of the DEAEMA residue, as indicated by the surface activity of the copolymers, was found to depend on the nature of the additional components: covalently linked hydrophobic groups (BMA) moderated the pH response of the copolymer as compared to nonionic and hydrophilic groups as in poly(O950)-b-(DEAEMA). These results suggest that mutual interactions among the building blocks of self-assembling copolymers should be taken into account when designing responsive copolymers.

Utilising alternative modifications of α-olefin end groups to synthesise amphiphilic block copolymers

Amphiphilic block copolymers comprised of polyisobutylene (PIB) and poly(2-(dimethylamino)ethyl methacrylate) (DMAEMA) have been synthesised.

Amino-functionalized poly(N-vinylcaprolactam) derived from lysine: a sustainable polymer with thermo and pH dual stimuli response

Lysine, a renewable feedstock with economic feasibility, was tactfully cyclized to its corresponding cyclic lysine and then subjected to a reaction with acetylenes to yield a sustainable N-vinylcaprolactam (VCL) derivative. Well-defined PVCL with pendent amino groups was prepared via MADIX/RAFT polymerization.

Conventional fluorophore-free dual pH- and thermo-responsive luminescent alternating copolymer

Herein, we have designed and synthesized a novel traditional fluorophore-free water-soluble fluorescent copolymer based on a poly(maleimide-alt-styrene) skeleton, which responds to both pH and temperature in aqueous medium.

Polyisobutylene-Based pH-Responsive Self-Healing Polymeric Gels

This work demonstrates the successful application of dynamic covalent chemistry for the construction of self-healing gels from side-chain primary amine leucine pendant diblock copolymers of polyisobutylene (PIB) ((P(H2N-Leu-HEMA)-b-PIB)) in the presence of PIB based dialdehyde functionalized cross-linker (HOC-PIB-CHO) through imine (-HC═N-) bond formation without aiding any external stimuli. Gels were synthesized in 1,4-dioxane at room temperature at varied wt % of gelator concentration, [H2N]/[CHO] ratios and molecular weight of the block segments. The mechanical property of gels was examined by rheological measurements. We observed higher value of storage modulus (G') than the loss modulus (G″) within the linearity limits of deformation, indicating the rheological behavior in the gel is dominated by an elastic property rather than a viscous property. The G' values significantly depend upon the extent of cross-linking in the gel network. To establish self-healing property of the gels, rheology analysis through step-strain measurements (strain = 0.1 to 200%) at 25 °C was performed. The polymeric gel network shows reversible sol-gel transition for several cycles by adjusting the pH of the medium with the help of hydrochloric acid (HCl) and triethylamine (Et3N) triggers. FT-IR spectroscopy established formation of imine bonds in the gel network and these gels showed poor swelling behavior in various organic solvents because of the small interstitial porosity, confirmed by field emission-scanning electron microscopy (FE-SEM).

Polymerization-induced self-assembly driving chiral nanostructured materials

Amino acid coated chiral nanostructured soft materials are made by the polymerization induced self-assembly (PISA) technique, where the post-polymerization chemical group transformation leads to a morphological transition.

A facile synthesis of branched graft copolymers via combination of RAFT self-condensing vinyl polymerization and aldehyde–aminooxy reaction

A facile synthetic route to the branched graft copolymer BPDEM-g-PEO has been developed by combination of the RAFT-SCVP technique and aldehyde–aminooxy reaction.

Specific counterion repercussions on the thermal, pH-response, and electrochemical properties of side-chain leucine based chiral polyelectrolytes

Effects of counterions of side chain amino acid based polyelectrolytes (PEs) on the solubility in aqueous medium, pH responsiveness, thermal properties, and ionic conductivities have been appraised. Deprotection of the tert-butyl carbamate (Boc) group from poly(Boc-l-leucine methacryloyloxyethyl ester) [P(Boc-l-Leu-HEMA)] was carried out to produce PE with trifluoroacetate as an associative counteranion (1a). PEs with bis(trifluoromethylsulfonyl)imide and hexafluorophosphate counteranion were prepared through anion exchange reactions of 1a. Protonation of the neutralized polymer (2) obtained from 1a, followed by anion exchange, leads to the production of miscellaneous PEs bearing different counteranions, such as tetrafluoroborate, trifluoromethanesulfonate, chloride, and nitrate. Differential scanning calorimetry traces of the PEs reveal that the comparatively larger and weakly coordinated counteranions require less thermal energy to dissociate, and thus, the glass transition temperature (Tg) of the PEs fall off with an increase in the size of the counteranion. A remarkable conductivity of 2.1 mS/cm was obtained in deionized water when Cl(-) acted as the counteranion. Steric and electronic factors of the counteranion induce a change of transition pH in different PEs, although the chiroptical nature was retained, as confirmed by circular dichroism spectroscopy.