Homo‐ and diblock copolymers of poly(furfuryl glycidyl ether) by living anionic polymerization: Toward reversibly core‐crosslinked micelles

We report the synthesis and characterization of well‐defined homo‐ and diblock copolymers containing poly(furfuryl glycidyl ether) (PFGE) via living anionic ring‐opening polymerization using different initiators. The obtained materials were characterized by SEC, MALDI‐TOF MS, and ¹H NMR spectroscopy and molar masses of up to 9400 g/mol were obtained for PFGE homopolymers. If the amphiphilic diblock copolymer PEG‐block‐PFGE was dissolved in water, micelles with a PFGE core and a PEG corona were formed. Hereby, the hydrophobic PFGE core domains were used for the incorporation of a suitable bismaleimide and heating to 60 °C induced the crosslinking of the micellar core via Diels‐Alder chemistry. This process was further shown to be reversible. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Segmented block copolyesters using click chemistry

Copper(I) catalyzed azide‐alkyne 1,3‐Huisgen cycloaddition reaction afforded the synthesis of triazole‐containing polyesters and segmented block copolyesters at moderate temperatures. Triazole‐containing homopolyesters exhibited significantly increased (～40 °C) glass transition temperatures (T_g) relative to high temperature, melt synthesis of polyesters with analogous structures. Quantitative synthesis of azido‐terminated poly(propylene glycol) (PPG) allowed for the preparation of segmented polyesters, which exhibited increased solubility and mechanical ductility relative to triazole‐containing homopolyesters. Differential scanning calorimetry demonstrated a soft segment (SS) T_g near ?60 °C for the segmented polyesters, consistent with microphase separation. Tensile testing revealed Young's moduli ranging from 7 to 133 MPa as a function of hard segment (HS) content, and stress at break values approached 10 MPa for 50 wt % HS segmented click polyesters. Dynamic mechanical analysis demonstrated an increased rubbery plateau modulus with increased HS content, and the T_g's of both the SS and HS did not vary with composition, confirming microphase separation. Atomic force microscopy also indicated microphase separated and semicrystalline morphologies for the segmented click polyesters. This is the first report detailing the preparation of segmented copolyesters using click chemistry for the formation of ductile membranes with excellent thermomechanical response. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Visualization of arborescent architecture of polystyrenes prepared by raft‐based initiator‐monomer polymerization using atomic force microscopy

This article presents the utilization of “molecular amplification” to visualize the molecular architecture of “arborescent” (tree‐like) polystyrenes (arbPSs) using atomic force microscopy (AFM). arbPSs with M_n > 80,000 g/mol were synthesized via initiator‐monomer‐type (inimer) RAFT polymerization of styrene mediated by 4‐vinylbenzyl dithiobenzoate in bulk. These arbPS were then used as macrochain transfer agents for polymerization of vinylbenzyl chloride (VBCl) to give arborescent poly(styrene‐block‐vinylbenzyl chloride) (arbPS‐b‐VBCl). Poly(styryl) diphenylethyl lithium (M_n = 11,000 g/mol) was then grafted onto the VBCl units of the arbPS‐b‐VBCl. The M_n of the amplified arbPSs increased over >10 million g/mol, exceeding the exclusion limit of our size exclusion chromatography equipment. AFM confirmed the proposed branches on branches architecture in the samples, together with lesser branched species. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Mimicking the cell membrane with block copolymer membranes

Cell membranes are essential barriers in Nature. To understand their properties and functions and to develop desirable applications, a simple and elegant approach is to study membranes that mimic the cell membrane. Lipid bilayers represent simple models that are physiologically representative when in the form of mixtures of various lipids, but they are not adequately stable even when covered with amphipathic proteins or when combined with polymers, thus preventing technological applications. This makes necessary the design of completely synthetic membranes. In this respect, amphiphilic copolymers that self‐assemble under dilute aqueous conditions and generate supramolecular polymer vesicles or films are ideal candidates for synthetic membranes. Their versatility in terms of chemistry and properties (permeability, mechanical stability, thickness), if appropriately designed, enable the insertion of biological molecules, such as membrane proteins and biopores, or the attachment of biomolecules at their surfaces. Here, we present the domain of synthetic membranes based on amphiphilic copolymers beginning with their generation and up to their applications in medicine, the food industry, and technology. Even though significant progress has been made in combining them with membrane proteins, open questions remain with respect to desired properties that could accommodate biological molecules and support further development of the field, from both the point of view of fundamental understanding and of applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Molecular and morphological characterization of midblock‐sulfonated styrenic triblock copolymers

Midblock‐sulfonated triblock copolymers afford a desirable opportunity to generate network‐forming amphiphilic materials that are suitable for use in a wide range of emerging technologies as fuel‐cell, water‐desalination, ion‐exchange, photovoltaic, or electroactive membranes. Employing a previously reported synthetic strategy wherein poly(p‐tert‐butylstyrene) remains unreactive, we have selectively sulfonated the styrenic midblock of a poly(p‐tert‐butylstyrene‐b‐styrene‐b‐p‐tert‐butylstyrene) (TST) triblock copolymer to different extents. Comparison of the resulting sulfonated copolymers with results from our prior study provides favorable quantitative agreement and suggests that a shortened reaction time is advantageous. An ongoing challenge regarding the morphological development of charged block copolymers is the competition between microphase separation of the incompatible blocks and physical cross‐linking of ionic clusters, with the latter often hindering the former. Here, we expose the sulfonated TST copolymers to solvent‐vapor annealing to promote nanostructural refinement. The effect of such annealing on morphological characteristics, as well as on molecular free volume, is explored. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 490–497     

Structural studies and quantum chemical calculations of Cr(III), Fe(III) and Ru(III) bromazepam complexes

The reaction of bromazepam (7‐bromo‐1,3‐dihydro‐5‐(2‐pyridyl)‐2H ‐1,4‐benzodiazepin‐2‐one, BZM) with Cr(III) ( 1 ), Fe(III) ( 2 ) and Ru(III) ( 3 ) salts gives complexes of the type [M(BZM)₃]⋅3X (X = Cl or NO₃). Structural characterization was extensively carried out using various analytical and spectral tools such as infrared, ¹H NMR and UV–visible spectroscopies and magnetic, conductance, elemental and thermal analyses. BZM is a bidentate ligand and interacts with the metal ions via the pyridine and benzodiazepin‐2‐one nitrogen atoms. The magnetic and electronic properties of 2 and 3 are consistent with low‐spin octahedral complexes. The three BZM molecules are non‐isoenergetically coordinated to the metal ions and this is reflected in the values of the second‐order interaction energy. The antibacterial activity was studied using Staphylococcus aureus and Escherichia coli . Coordination of BZM to Cr(III) or Ru(III) ions leads to a marked increase in toxicity with respect to the inactive Fe(III) complex 2 .     

RAFT synthesis of an amphiphilic block copolymer bearing chlorin rings in the hydrophobic segment and its application in photodynamic therapy

RAFT polymerization of styrene (St) in the presence of 5,10,15,20‐tetrakis(pentafluorophenyl)porphyrin (TFPP) was conducted using 4‐cyano‐4‐(thiobenzoyl)thiopentanoic acid as a chain‐transfer agent and azobisisobutyronitrile as an initiator at 60 °C. The resulting polymer exhibited a chlorin‐like UV‐vis spectrum, which indicated that the polymer possessed a reduced TFPP structure. Furthermore, an SEC trace recorded using UV‐vis detector (λ = 410 nm), which selectively detected the TFPP‐incorporated polymer, shifted toward higher molecular mass as the polymerization progressed. This evidence indicated that TFPP acted as a vinylene‐type monomer, such as maleimide, to form a copolymer, namely, poly(St‐co‐TFPP). The mole fraction of TFPP units was estimated to be 0.74 × 10^?3, which was close to that in the feed (1 × 10^?3). Chain extension of poly(St‐co‐TFPP) with polyethylene glycol monomethyl ether acrylate (PEGA) was performed to afford the amphiphilic block copolymer poly(St‐co‐TFPP)‐b‐poly(PEGA). The degrees of polymerization of St and PEGA were determined to be 64 and 75, respectively. Poly(St‐co‐TFPP)‐b‐poly(PEGA) formed micelles following dialysis. The median diameter of the micelles in solution was determined to be 16 nm by DLS. The photocytotoxicity of the micelle solution was evaluated in a human glioblastoma cell line (U251) and an N‐methyl‐N'‐nitro‐N‐nitrosoguanidine‐induced mutant of a rat murine RGM‐1 gastric carcinoma mucosal cell line (RGK‐1). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 3395–3403     

Magnetization switching modes in nanopillar spin valve under the external field

The current-induced magnetic switching is studied in Co/Cu/Co nanopillar with an in-plane magnetization traversed under the perpendicular-to-plane external field.Magnetization switching is found to take place when the current density exceeds a threshold.By analyzing precessional trajectories,evolutions of domain walls and magnetization switching times under the perpendicular magnetic field,there are two different magnetization switching modes:nucleation and domain wall motion reversal;uniform magnetization ...