On the σ-dimerization of N,N-dimethyl-p-toluidine during anodic oxidation—A reinvestigation

The anodic oxidation of N,N-dimethyl-p-toluidine (2) was studied using cyclic voltammetry and spectroelectrochemistry. In contrast to former studies, the experimental measurements showed that the radical cations of 2 reversibly dimerize at the methyl substituted p-position of the dimethylamino group and form σ-dimers. Theses results again clearly demonstrate that σ-dimerization takes place even when reactive sites are blocked by substituents such as alkyl or phenyl groups. The findings are also relevant for the interpretation of σ-dimerization during electropolymerization and charging of conducting polymers.     

Synthesis of new N, N-diphenylhydrazone dyes for solar cells: Effects of thiophene-derived π-conjugated bridge

Four novel D-π-A hydrazone dyes (HT, HM, HE, and HO) with an N, N-diphenylhydrazone moiety as the electron donor, different thiophene-derived π-conjugated bridges and a cyanoacrylic acid moiety as the electron acceptor have been designed and synthesized for the application in dye-sensitized solar cells. The influences of thiophene-derived bridges on the photoelectrochemical and photovoltaic performance of these hydrazone dyes were investigated. Results demonstrate that the introduction of 3,4-dialkyloxythiophene could red-shift the dye’s absorption spectrum due to the enhancement of the electron-donating ability of π-conjugated bridges. Importantly, electrochemical impedance spectroscopy analysis reveal that 3,4-dialkyloxythiophene bridge could change the charge recombination resistance at the TiO₂/dye/electrolyte interface and as a result to improve the open-circuit photovoltage. Among the four dyes, HO exhibits the maximum power conversion efficiency of 5.83% (V_oc = 0.65 V, J_sc = 12.69 mA/cm², FF = 0.707) under simulated AM 1.5 irradiation (100 mW/cm²).     

Micellization and phase transition behavior of thermosensitive poly(N-isopropylacrylamide)-poly(?-caprolactone)-poly(N-isopropylacrylamide) triblock copolymers

Thermosensitive triblock copolymers with two hydrophilic poly(N-isopropylacrylamide) blocks flanking a central hydrophobic poly(?-caprolactone) block were synthesized by atom transfer radical polymerization. Core-shell micellization of the triblock copolymers was inferred from the ¹H NMR spectra derived in two different solvent environments (CDCl₃ and D₂O). The micellar characteristics of these amphiphilic triblock copolymers were studied by pyrene fluorescence techniques, dynamic light scattering and transmission electron microscopy. The critical micelle concentrations of the triblock copolymers were in the range of 4-16 mg/L and the partition coefficients were in the range of 3.10 × 10⁴ to 2.46 × 10⁵. The mean diameters of the micelles, measured by light scattering, were between 90 and 120 nm. The temperature sensitivity of the triblock copolymers was demonstrated by the phase transition of a 250 mg/L aqueous polymer solution at the lower critical solution temperature (LCST). The enthalpy of the phase transition was determined by differential scanning calorimetry. PM3 quantum mechanical calculation method was used to understand the intermolecular interactions between the copolymer and the water molecules. A modular approach was used to simulate the phase transition observed at the LCST.     

Poly(ε-caprolactone)-block-poly(N-vinyl pyrrolidone) diblock copolymers grafted from macrocyclic oligomeric silsesquioxane

Poly(ε-caprolactone)-block-poly(N-vinyl pyrrolidone) diblock copolymers grafted from macrocyclic oligomeric silsesquioxane (MOSS) (denoted MOSS[PCL-b-PVPy]₁₂) were synthesized via the sequential polymerizations involving ring-opening polymerization (ROP) of ε-caprolactone (CL) and RAFT/MADIX polymerization of N-vinyl pyrrolidone (NVP). The organic-inorganic brush-like diblock copolymers were characterized by means of nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC). Small angle X-ray scattering (SAXS) showed that all the MOSS[PCL-b-PVPy]₁₂ was microphase-separated in the amorphous state. The microphase-separated morphologies were quite dependent on the length of PVPy blocks and the crystallization behavior of PCL subchains was significantly affected by the lengths of PVPy subchains. In aqueous solutions, the MOSS[PCL-b-PVPy]₁₂ can be self-assembled into the polymeric micelles as evidenced by dynamic light scattering (DLS) and transmission election microscopy (TEM). The critical micelle concentrations of the brush-like diblock copolymers increased with increasing the lengths of PVPy blocks. It is proposed that the stability of the micellar cores was increased with the macrocyclic molecular brush structure of the diblock copolymers and the formation of the MOSS aggregates via MOSS–MOSS interactions.     

Novel acid-degradable and thermo-sensitive poly(N-isopropylacrylamide) hydrogels cross-linked by α,α-trehalose diacetals

New trehalose-containing hydrogels and the first hydrogels cross-linked by mono- or disaccharide acetals that are degradable in acidic medium were designed and synthesized. The cross-linking agent was obtained in acetalization reaction of trehalose with x-allyloxybenzaldehyde in which diallyl compounds were formed and used afterward in free radical copolymerization with N-isopropylacrylamide (NIPAAm) to provide thermo-sensitive hydrogels. Depending on the trehalose diacetal isomer and solvent system used in copolymerization, as well the degree of network cross-linking, these hydrogels differed in morphology, swelling and deswelling behavior and time of degradation. Compared with conventional PNIPAAm hydrogels they are degradable what makes them good materials for biomedical applications.     

Synthesis of poly(N-vinyl carbazole)-based block copolymers by sequential polymerizations of RAFT–ATRP

Poly(N-vinylcarbazole) (PNVK) is one of the extensively studied photoconductive polymers because of its wide ranges of applications. Through the reversible addition-fragmentation chain transfer/macromolecular design via the interchange of xanthates (RAFT/MADIX) polymerizations, in this study we investigated the syntheses of PNVK-based block copolymers (BCPs) with styrene (St) and methyl methacrylate (MMA). A variety of difunctional haloester-xanthate inifers were prepared and subjected to sequential polymerizations through RAFT and ATRP. In the presence of small amounts of bromoxanthate inifers, the ¹H NMR spectra showed nearly complete consumption of the NVK monomer, but without formation of PNVK. The bromoxanthate inifer could act as acidic moieties that protonated the highly basic NVK monomer. Through ¹H NMR and MALDI-TOF spectroscopic analyses, the structures of byproducts were indentified and a plausible mechanism for their formation was proposed. Alternatively, RAFT/MADIX polymerizations of NVK with two chloroxanthate inifers S-[1-methyl-4-(6-chloropropionate)ethyl acetate] O-ethyl dithiocarbonate and S-[1-methyl-4-(6-chloroisobutyrate)ethyl acetate] O-ethyl dithiocarbonate) provided first-order kinetic plots and well-controlled PNVK-Cl MIs (M_n ≈ 6000–40,000; M_w/M_n < 1.35). Using a suitable ATRP-initiating groups and optimization of the reaction conditions, the BCPs PNVK-b-PSt (M_n ≈ 4900–12,800; M_w/M_n < 1.5) and PNVK-b-PMMA (M_n ≈ 46,000–100,000; M_w/M_n < 1.35) were obtained.     

Titanium precatalysts bearing N-substituted β-amino alcohols for 1-hexene polymerization: The effect of steric crowding

A series of titanium-based non-metallocene precatalysts [2-(2,6-dialkylphenylamino)-1-phenylethoxy TiCl₂ were prepared by reacting lithium salts of the corresponding amino alcohols with TiCl₄(THF)₂. Upon activation with methylaluminoxane (MAO), these precatalysts polymerized 1-hexene in isotactic manner. The catalyst activity and polymer properties depended on the steric features in the ortho positions of the aniline moiety of the ligands. As the bulkiness of the alkyl group in ortho positions of the aniline moiety increased, the catalyst showed better activity with high molecular weight and greater tacticity control. For 1-hexene polymerization, precatalyst 1ATiCl₂ showed activity of 3.05 kg of PH/mol-Ti.h at room temperature and the resulting polyhexene had molecular weight of 403,600 (M_w/M_n=1.40) with 80% isotacticity (mmmm). The dibenzylic titanium complexes 1ATi(CH₂Ph)₂ and 3ATi(CH₂Ph)₂, upon activation with MAO or Ph₃CB(C₆F₅)₄, showed relatively lower activities towards 1-hexene polymerization, yielding polymers of lower molecular weights but with narrow molecular weight distribution.     

Chiral separation of racemic amino acids with novel polyamides having N-α-acetyl-l-glutamyl residue as a diacid component

Novel polyamides with asymmetric carbons in their main chains were obtained from aromatic diamines, 4,4′-diaminodiphenylmethane (DADPM) or 1,3-phenylenediamine (1,3-PDA), and N-α-protected l-glutamic acid, N-α-acetyl-l-glutamic acid (Ac-l-Glu-OH). Newly prepared polyamides showed optical rotation, implying that optically active polyamides were successfully obtained in the present study. These two types of chiral polyamides showed chiral recognition ability, which was studied by surface plasmon resonance (SPR) spectroscopy; they recognized d-glutamic acid in preference to the corresponding l-isomer. The adsorption selectivity was determined to be 1.66 for 1,3-PDA-Ac-l-Glu and 1.49 for DADPM-Ac-l-Glu. Enantioselective electrodialysis was studied adopting racemic N-α-acetyl-tryptophan (Ac-Trp) mixtures as model pairs of enantiomers. The membranes selectively transported Ac-d-Trp. Permselectivity toward the d-isomer reached 2.03.     

Fabrication of star-shaped, thermo-sensitive poly(N-isopropylacrylamide)-cholic acid-poly(?-caprolactone) copolymers and their self-assembled micelles as drug carriers

Novel star-shaped copolymers, comprised of a thermo-sensitive poly(N-isopropylacrylamide) (PNIPAAm) segment and three hydrophobic poly(?-caprolactone) (PCL) arms were fabricated. The copolymers were prepared by stannous octoate (Sn(Oct)₂) catalyzed ring-opening polymerization of ?-caprolactone (CL) using cholic acid functionalized PNIPAAm as the macroinitiator. The lower critical solution temperatures (LCST) of the copolymer solutions are attractively close to the nominal physiologic temperature at around 37 °C. The in vitro cytotoxicity test indicated no apparent cytotoxicity. The amphiphilic star-shaped copolymers were capable of self-assembling into spherical micelles in water at room temperature, and they possessed low critical micelle concentrations (CMCs) of 3 ∼ 8 mg/L in aqueous solution determined by fluorescence spectroscopy using pyrene as a probe. Transmission electron microscopy (TEM) measurement showed that the micelles exhibited a spherical shape with a size range of 30 ∼ 75 nm in diameter. In addition, the anticancer drug, methotrexate (MTX) can be loaded effectively in the polymeric micelles and its release was temperature-stimulated, which suggests that these materials have good potential as “intelligent” drug carriers.     

Synthesis and characterization of chiral polythiophenes: Poly [(R)-(−) and (S)-(+)-2-(3′-thienyl)ethyl N-(3″,5″-dinitrobenzoyl)-α-phenylglycinate]

(R)-(−) (1) and (S)-(+)-2-(3′-Thienyl)ethyl N-(3″,5″-dinitrobenzoyl)-α-phenylglycinate (2) monomers were synthesized, characterized, and polymerized in chloroform using FeCl₃ as an oxidizing agent. Molecular weights of 2.6 × 10⁴ and 3.2 × 10⁴ for poly1 and poly2, respectively, were determined by SEC analysis. FTIR spectra of the polymers indicated the coupling of monomers through the α positions. UV-vis spectra showed absorption bands at λ_max = 226 and 423 nm for poly1 and poly2, ascribed to transitions of side groups and polythiophene backbone, respectively. Poly1 and poly2 remained stable up to 210 °C. At higher temperatures, a two step weight loss degradation process was observed for both polymers by TGA analysis. ¹H NMR, in the presence of Eu(tfc)₃, and optical rotation measurements indicate the chiral properties of the monomers 1 ([α]_D²⁸ = −76.2) and 2 ([α]_D²⁸ = +76.0), and the maintenance of chirality after polymerization (poly1 [α]_D²⁸ = −29.0 and poly2 [α]_D²⁸ = +28.4, c = 2.5 in THF). According to scanning electron microscopic analysis, the polymers are highly porous.     

Structure and superconducting properties of layered perovskite-like compounds Y1 ? 2xCaxPrxBa2Cu3Oy and Y1 ? xBa2PrxCu3 ? xZnxOy

The conditions of preparation of Y_{1 − x} Pr _x Ba₂Cu_{3 − x} Zn _x O _y and Y_{1 − 2x} Ca _x Pr _x Ba₂Cu₃O _y solid solutions with an Y-123-type structure in the orthorhombic crystal system by the method of solid-phase chemical reactions have been determined. The concentration dependences of the unit cell parameters for these solid solutions have been established. The temperature dependences of the resistivity of the synthesized compounds have been investigated, the critical temperatures of the superconducting transition have been determined, and their variation as a function of the type and content of the introduced dopants has been analyzed. It has been demonstrated that, in the Y_{1 − x} Pr _x Ba₂Cu_{3 − x} Zn _x O _y samples, individual dopants have a combined effect on the suppression of the superconducting properties, whereas in the Y_{1 − 2x} Ca _x Pr _x Ba₂Cu₃O _y samples, calcium and praseodymium ions interact with each other when they are simultaneously introduced into the yttrium sublattice.     

CR/SBS/CEVA-g-MMA/n-BMA胶粘剂的研制

以ＣＲ、苯乙烯丁二烯苯乙烯嵌段共聚物（ＳＢＳ）和氯化乙烯乙酸乙烯酯共聚物（ＣＥＶＡ）３种固体物料为接枝母体,以甲基丙烯酸甲酯（ＭＭＡ）和甲基丙烯酸正丁酯（ｎＢＭＡ）为接枝单体,在溶剂回流温度下,空气氛围中,以过氧化二苯甲酰（ＢＰＯ）为引发剂进行接枝共聚,制得了共混接枝共聚胶粘剂。此种胶粘剂的单体转化率、接枝率、初粘强度都有较大的提高,其广谱性能也有所改善。