Selenolactone as a Building Block toward Dynamic Diselenide-Containing Polymer Architectures with Controllable Topology

A versatile protocol for the synthesis of a variety of multiresponsive diselenide-containing polymeric architectures was investigated. It consists of a one-pot, two-step process with the generation of a selenol by in situ nucleophilic ring opening of selenolactone with a broad range of amine-containing structures, followed by the transformation of the obtained compounds to the corresponding diselenide through a spontaneous oxidation coupling reaction. After elaboration of this one-pot reaction, a number of routes based on selenolactones have been developed for the successful synthesis of functional, linear, branched, cyclic, and cross-linked polymers via a mild, straightforward process. Moreover, the polymer end groups can be easily modified by changing the ratio of amine and selenolactone or sequential Michael addition of selenol to the methacrylic ester. At last, the self-healing properties of the diselenide-containing networks were determined by exposing a cut sample of the polymer to UV light

Circularly Polarized Light with Sense and Wavelengths To Regulate Azobenzene Supramolecular Chirality in Optofluidic Medium

Circularly polarized light (CPL) as a massless physical force causes absolute asymmetric photosynthesis, photodestruction, and photoresolution. CPL handedness has long been believed to be the determining factor in the resulting product’s chirality. However, product chirality as a function of the CPL handedness, irradiation wavelength, and irradiation time has not yet been studied systematically. Herein, we investigate this topic using achiral polymethacrylate carrying achiral azobenzene as micrometer-size aggregates in an optofluidic medium with a tuned refractive index. Azobenzene chirality with a high degree of dissymmetry ratio (±1.3 × 10^–2 at 313 nm) was generated, inverted, and switched in multiple cycles by irradiation with monochromatic incoherent CPL (313, 365, 405, and 436 nm) for 20 s using a weak incoherent light source (≈ 30 μW·cm^–2). Moreover, the optical activity was retained for over 1 week in the dark. Photoinduced chirality was swapped by the irradiating wavelength, regardless of whether the CPL sense was the same. This scenario is similar to the so-called Cotton effect, which was first described in 1895. The tandem choice of both CPL sense and its wavelength was crucial for azobenzene chirality. Our experimental proof and theoretical simulation should provide new insight into the chirality of CPL-controlled molecules, supramolecules, and polymers

Developing a Synthetic Approach with Thermoregulated Phase-Transfer Catalysis: Facile Access to Metal-Mediated Living Radical Polymerization of Methyl Methacrylate in Aqueous/Organic Biphasic System

A novel strategy via thermoregulated phase-transfer catalysis (TRPTC) to separating catalyst in aqueous/organic biphasic system has been successfully established in a copper-mediated activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP) of methyl methacrylate (MMA), using a thermoresponsive PEG-supported dipyridyl ligand (PSDL) as the ligand and an alkyl pseudohalogen 2-cyanoprop-2-yl 1-dithionaphthalate (CPDN) as the initiator. The catalyst complex can transfer into the organic phase from initial catalyst aqueous solution at the reaction temperature (90 °C) to catalyze the homogeneous polymerization of MMA and then retransfer into the aqueous solution from the organic phase to separate the catalyst from the polymerization solution once cooled to room temperature (25 °C) while remaining well-controlled product (PMMA) in organic layer. In addition, the polymerization can be conducted in the presence of a limited amount of air, which not only does not sacrifice the controllability over polymerization but also can recycle the catalyst just by a simple change of the temperatures effectively

Facilely Recyclable Cu(II) Macrocomplex with Thermoregulated Poly(ionic liquid) Macroligand: Serving as a Highly Efficient Atom Transfer Radical Polymerization Catalyst

Copolymer poly­(ionic liquids) (PILs) are fascinating new polymerized polyelectrolytes that can provide the properties of ionic liquids with others combined into one. In this work, a thermoregulated random copolymer PIL (PILL) with the side chains of both ionic liquids and atom transfer radical polymerization (ATRP) ligands was designed and synthesized to form a macrocomplex with CuBr₂ and serve as an ATRP catalyst to establish a thermoregulated phase separated catalysis (TPSC) system and further applied in a typical ICAR (initiators for continuous activator regeneration) ATRP process for the catalyst separation and recycling <i>in situ</i> for the first time. This novel TPSC system could simultaneously recycle transition metal catalyst and ligand easily just by changing temperature from polymerization temperature to room temperature. Additionally, even if the highly efficient recyclable PILL with Cu catalyst was separated facilely and reused 10 times <i>in situ</i>, it nearly did not sacrifice the controllability over polymerization. Furthermore, after polymerization and a TPSC process, the metal catalyst residual in the polymer solution phase remained just about 1.5 ppm, indicating highly efficient transition metal catalyst recycling efficiency

Facile Fabrication of Biocompatible and Tunable Multifunctional Nanomaterials via Iron-Mediated Atom Transfer Radical Polymerization with Activators Generated by Electron Transfer

A novel strategy of preparing multifunctional nanoparticles (NPs) with near infra red (NIR) fluorescence and magnetism showing good hydrophilicity and low toxicity was developed via surface-initiated atom transfer radical polymerization with activators generated by electron transfer (AGET ATRP) of poly­(ethylene glycol) monomethyl ether methacrylate (PEGMA) and glycidyl methacrylate (GMA) employing biocompatible iron as the catalyst on the surface of silica coated iron oxide (Fe₃O₄@SiO₂) NPs. The small molecules (CS2), a NIR fluorescent chromophore, can be fixed into the covalently grafted polymer shell of the NPs by chemical reaction through a covalent bond to obtain stable CS2 dotted NPs Fe₃O₄@SiO₂@PPEGMA-<i>co</i>-PGMA@CS2. The fluorescence intensity of the as-prepared NPs could be conveniently regulated by altering the silica shell thickness (varying the feed of silica source TEOS), CS2 feed, or the feed ratio of <i>V</i>_PEGMA/<i>V</i>_GMA, which are easily realized in the preparation process. Thorough investigation of the properties of the final NPs including <i>in vivo</i> dual modal imaging indicate that such NPs are one of the competitive candidates as imaging agents proving a promising potential in the biomedical area

Reversibly Shielded DNA Polyplexes Based on Bioreducible PDMAEMA-SS-PEG-SS-PDMAEMA Triblock Copolymers Mediate Markedly Enhanced Nonviral Gene Transfection

Reversibly shielded DNA polyplexes based on bioreducible poly­(dimethylaminoethyl methacrylate)-SS-poly­(ethylene glycol)-SS-poly­(dimethylaminoethyl methacrylate) (PDMAEMA-SS-PEG-SS-PDMAEMA) triblock copolymers were designed, prepared and investigated for in vitro gene transfection. Two PDMAEMA-SS-PEG-SS-PDMAEMA copolymers with controlled compositions, 6.6–6–6.6 and 13–6–13 kDa, were obtained by reversible addition–fragmentation chain transfer (RAFT) polymerization of dimethylaminoethyl methacrylate (DMAEMA) using CPADN-SS-PEG-SS-CPADN (CPADN: 4-cyanopentanoic acid dithionaphthalenoate; PEG: 6 kDa) as a macro-RAFT agent. Like their nonreducible PDMAEMA-PEG-PDMAEMA analogues, PDMAEMA-SS-PEG-SS-PDMAEMA triblock copolymers could effectively condense DNA into small particles with average diameters less than 120 nm and close to neutral zeta potentials (0 ∼ +6 mV) at and above an N/P ratio of 3/1. The resulting polyplexes showed excellent colloidal stability against 150 mM NaCl, which contrasts with polyplexes of 20 kDa PDMAEMA homopolymer. In the presence of 10 mM dithiothreitol (DTT), however, polyplexes of PDMAEMA-SS-PEG-SS-PDMAEMA were rapidly deshielded and unpacked, as revealed by significant increase of positive surface charges as well as increase of particle sizes to over 1000 nm. Release of DNA in response to 10 mM DTT was further confirmed by gel retardation assays. These polyplexes, either stably or reversibly shielded, revealed a low cytotoxicity (over 80% cell viability) at and below an N/P ratio of 12/1. Notably, in vitro transfection studies showed that reversibly shielded polyplexes afforded up to 28 times higher transfection efficacy as compared to stably shielded control under otherwise the same conditions. Confocal laser scanning microscope (CLSM) studies revealed that reversibly shielded polyplexes efficiently delivered and released pDNA into the perinuclei region as well as nuclei of COS-7 cells. Hence, reduction-sensitive reversibly shielded DNA polyplexes based on PDMAEMA-SS-PEG-SS-PDMAEMA are highly promising for nonviral gene transfection

Supramolecular Chirality in Achiral Polyfluorene: Chiral Gelation, Memory of Chirality, and Chiral Sensing Property

Producing supramolecular chirality from achiral π-conjugated polymers toward preferred chiral memory, effective circularly polarized luminescence, and chiral sensor is extremely important in design of functional chiral materials. Proposed herein is an effective protocol to generate and memorize the supramolecular chirality formed from achiral poly­(9,9-dioctyl­fluorene) (PF8) induced by chiral solvation. The process of chiral supramolecular assembly was monitored by UV–vis spectroscopy, circular dichroism (CD), and fluorescent spectroscopy. Achiral PF8 dissolved in neat (<i>R</i>)-(+)-limonene (1<i>R</i>) and (<i>S</i>)-(−)-limonene (1<i>S</i>) underwent chiral sol–gel transition at −20 °C. PF8 aggregates revealed intense CD and circularly polarized luminescence (CPL) signals due to β-phase, exhibiting absolute dissymmetry ratio of ≈2 × 10^–3 at 430–470 nm. The supramolecular chirality of PF8 aggregates can be perfectly memorized in solid film even near decomposition temperature (300 °C), comparing favorably with that from chiral polyfluorene. Atomic force microscopy (AFM) inferred helically distorted PF8 aggregate motifs responsible for the CD and CPL functionality. Furthermore, the first chiral sensor to detect nonracemic limonene molecules employing achiral PF8 spin-cast film from CHCl₃ solution was achieved

Natural RAFT Polymerization: Recyclable-Catalyst-Aided, Opened-to-Air, and Sunlight-Photolyzed RAFT Polymerizations

The successful sunlight-photolyzed reversible addition–fragmentation chain transfer (RAFT) photopolymerization can be reversibly activated and deactivated by irradiation with sunlight in the absence of photocatalyst and photoinitiator. In the present work, the thiocarbonylthio compounds (dithiobenzoate, trithiocarbonate, and xanthate) can all be employed to carry out the polymerization under sunlight irradiation acting as an initiator, chain transfer agent, and termination agent. Moreover, it was demonstrated that the recyclable-catalyst-aided, opened-to-air, and sunlight-photolyzed RAFT (ROS-RAFT) polymerizations can be successfully carried out to fabricate precise and predictable polymers in the presence of the recyclable magnetic semiconductor nanoparticles (NPs). The oxygen tolerance is likely attributed to a specific interaction between NPs and oxygen

A Straightforward Protocol for the Highly Efficient Preparation of Main-Chain Azo Polymers Directly from Bisnitroaromatic Compounds by the Photocatalytic Process

A novel strategy for the synthesis of main-chain Azo polymers directly from bisnitroaromatic compounds by the photocatalytic process has been achieved under mild conditions. This approach avoids the tedious synthesis of Azo monomers and proceeds with a high monomer conversion (∼100%) and excellent selectivity (∼100%) but without generating a significant amount of inorganic wastes and impurities (Cu²⁺ or azoxy groups) existing in main-chain Azo polymers compared to previous methods. The polymerization was monitored by UV–vis, FT-IR, and MALDI-TOF-MS, indicating that the reaction process proceeded with formation of the azoxy repeating units from the corresponding bisnitroaromatic monomers and the reduction of corresponding azoxy repeating units to the azo repeating units. Furthermore, the recyclable heterogeneous photocatalysts represent an attractive green process for production of main-chain Azo polymers