Living Covalent-Anionic-Radical Polymerization via a Barbier Strategy

The developments of the living alkene polymerization method have achieved great progress and enabled the precise synthesis of important polyalkenes with controlled molecular weight, molecular weight distribution, and architecture through an anionic, cationic or radical strategy. However, it is still challenging to develop a living alkene polymerization method through an all-in-one strategy where anionic and radical characteristics are merged into one polymerization species. Here, a versatile living polymerization method is reported by introducing a well-established all-in-one covalent-anionic-radical Barbier strategy into a living polymerization. Through this living covalent-anionic-radical Barbier polymerization (Barbier CARP), narrow distributed polystyrenes, with Đ as low as 1.05, are successfully prepared under mild conditions with a full monomer conversion by using wide varieties of organohalides, for example, alkyl, benzyl, allyl, and phenyl halides, as initiators with Mg in one pot. This living covalent-anionic-radical polymerization via a Barbier strategy expands the methodology library of polymer chemistry and enables living polymerization with an unconventional polymerization mode.

Recent Advances in the Synthesis of Complex Macromolecular Architectures Based on Poly(N-vinyl pyrrolidone) and the RAFT Polymerization Technique

Recent advances in the controlled RAFT polymerization of complex macromolecular architectures based on poly(N-vinyl pyrrolidone), PNVP, are summarized in this review article. Special interest is given to the synthesis of statistical copolymers, block copolymers, and star polymers and copolymers, along with graft copolymers and more complex architectures. In all cases, PNVP is produced via RAFT techniques, whereas other polymerization methods can be employed in combination with RAFT to provide the desired final products. The advantages and limitations of the synthetic methodologies are discussed in detail.

Mechanism of the Arene-Limited Nondirected C-H Activation of Arenes with Palladium*

Recently palladium catalysts have been discovered that enable the directing-group-free C-H activation of arenes without requiring an excess of the arene substrate, thereby enabling methods for the late-stage modification of complex organic molecules. The key to success has been the use of two complementary ligands, an N-acyl amino acid and an N-heterocycle. Detailed experimental and computational mechanistic studies on the dual-ligand-enabled C-H activation of arenes have led us to identify the catalytically active species and a transition state model that explains the exceptional activity and selectivity of these catalysts. These findings are expected to be highly useful for further method development using this powerful class of catalysts.

Pharmaceutical assessment of polyvinylpyrrolidone (PVP): As excipient from conventional to controlled delivery systems with a spotlight on COVID-19 inhibition

Polyvinylpyrrolidone (PVP) is a water-soluble polymer obtained by polymerization of monomer N-vinylpyrrolidone. PVP is an inert, non-toxic, temperature-resistant, pH-stable, biocompatible, biodegradable polymer that helps to encapsulate and cater both hydrophilic and lipophilic drugs. These advantages enable PVP a versatile excipient in the formulation development of broad conventional to novel controlled delivery systems. PVP has tunable properties and can be used as a brace component for gene delivery, orthopedic implants, and tissue engineering applications. Based on different molecular weights and modified forms, PVP can lead to exceptional beneficial features with varying chemical properties. Graft copolymerization and other techniques assist PVP to conjugate with poorly soluble drugs that can inflate bioavailability and even introduces the desired swelling tract for their control or sustained release. The present review provides chemistry, mechanical, physicochemical properties, evaluation parameters, dewy preparation methods of PVP derivatives intended for designing conventional to controlled systems for drug, gene, and cosmetic delivery. The past and growing interest in PVP establishes it as a promising polymer to enhance the trait and performance of current generation pharmaceutical dosage forms. Furthermore, the scrutiny explores existing patents, marketed products, new and futuristic approaches of PVP that have been identified and scope for future development, characterization, and its use. The exploration spotlights the importance and role of PVP in the design of Povidone-iodine (PVP-I) and clinical trials to assess therapeutic efficacy against the COVID-19 in the current pandemic scenario.

Probing Orientation-Specific Charge-Dipole Interactions between Hexafluoroisopropanol and Halides: A Joint Photoelectron Spectroscopy and Theoretical Study

The interactions between hexafluoroisopropanol (HFIP) and halogen anions X^- (F^-, Cl^-, Br^-, and I^-) have been investigated using negative ion photoelectron (NIPE) spectroscopy and ab initio calculations. The measured NIPE spectrum of each [HFIP·X]^- (X = Cl, Br, and I) complex shows a pattern identical to the corresponding X^- by shifting to the high electron binding energy side, indicative of the formation of the [HFIP···X^-] structure in which X^- interacts with HFIP via charge-dipole interactions. However, the spectrum of [HFIP·F]^- appears completely different from that of F^- and is more similar to the spectrum of the deprotonated HFIP anion (HFIP_-H^-). The geometry and electron density calculations indicate that a neutral HF molecule is formed upon HFIP interacting with F^- via proton transfer, rendering a stable structure of [HFIP_-H···HF]^-. Two conformers of [HFIP_-H·HF]^- with HFIP being in synperiplanar and antiperiplanar configurations, respectively, are observed, providing direct experimental evidences to show the distinctly different and orientation-specific interactions between HFIP and halide anions.

Facile synthesis of poly(N-vinyl pyrrolidone) block copolymers with “more-activated” monomers by using photoinduced successive RAFT polymerization

Well-defined PNVP block copolymers with more-activated monomers were synthesized by a single RAFT polymerization method under irradiation with visible light at room temperature.

RAFT Polymerization of Styrene and Maleimide in the Presence of Fluoroalcohol: Hydrogen Bonding Effects with Classical Alternating Copolymerization as Reference

The impacts of hydrogen bonding on polymerization behavior has been of interest for a long time; however, universality and in-depth understanding are still lacking. For the first time, the effect of hydrogen bonding on the classical alternating-type copolymerization of styrene and maleimide was explored. N-phenylmaleimide (N-PMI)/styrene was chosen as a model monomer pair in the presence of hydrogen bonding donor solvent 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), which interacted with N-PMI via hydrogen bonding. Reversible addition-fragmentation chain transfer polymerization (RAFT) technique was used to guarantee the "living" polymerization and thus the homogeneity of chain compositions. In comparison with the polymerization in nonhydrogen bonding donor solvent (toluene), the copolymerization in HFIP exhibited a high rate and a slight deviation from alternating copolymerization tendency. The reactivity ratios of N-PMI and St were revealed to be 0.078 and 0.068, respectively, while the reactivity ratios in toluene were 0.026 and 0.050. These interesting results were reasonably explained by using computer simulations, wherein the steric repulsion and electron induction by the hydrogen bonding between HFIP and NPMI were revealed. This work first elucidated the hydrogen bonding interaction in the classical alternating-type copolymerization, which will enrich the research on hydrogen bonding-induced polymerizations.

Temperature programed photo-induced RAFT polymerization of stereo-block copolymers of poly(vinyl acetate)

Stereo-triblock copolymers of poly(vinyl acetate) are synthesized with controlled molecular weights based on a temperature-programed photo-induced RAFT in HFIP.