Synthesis and characterization of well‐defined lactic acid–PEG cooligomers and its tricarbonyl rhenium conjugates

This article describes the synthesis and characterization of hydroxyl tailored, molecularly defined biodegradable cooligomers capable of chelating rhenium for potential radiopharmaceuticals. New insights were gained during the synthesis of lactide based on dimethylaminopyridine‐catalyzed transesterification. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis,characterization, and ethylene (Co)polymerization behavior of trichlorotitanium 2‐(1‐(arylimino)propyl)quinolin‐8‐olates

A series of trichlorotitanium complexes containing 2‐(1‐(arylimino)propyl)quinolin‐8‐olates was synthesized by stoichiometric reaction of titanium tetrachloride with the corresponding potassium 2‐(1‐(arylimino)propyl)quinolin‐8‐olates and was fully characterized by elemental analysis, nuclear magnetic resonance spectroscopy, and by single‐crystal X‐ray diffraction study of representative complexes. All titanium complexes, when activated with methylaluminoxane, exhibited high catalytic activity toward ethylene polymerization [up to 1.15 × 10⁶ g mol^?1(Ti) h^?1] and ethylene/α‐olefin copolymerization [up to 1.54 × 10⁶ g mol^?1 (Ti) h^?1]. The incorporation of comonomer was confirmed to amount up to 2.82 mol % of 1‐hexene or 1.94 mol % of 1‐octene, respectively. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Single electron transfer‐living radical polymerization of methyl methacrylate catalyzed by ytterbium powder

Zerovalent ytterbium (Yb) powder is firstly used as a catalyst in single electron transfer‐living radical polymerization of methyl methacrylate initiated by carbon tetrachloride in N, N‐dimethylformamide (DMF) and dimethyl sulfoxide, respectively. Polymerization proceeds in a “living”/controlled way as evidenced by kinetic studies and chain extension results, producing well‐defined polymers with controlled degree of polymerization and narrow molecular weight distribution. The apparent activation energy of polymerization in DMF is accounted to be 36.2 kJ/mol, and the energy of equilibrium state is calculated to be 13.9 kJ/mol. An increase in the concentration of Yb(0) yields a higher monomer conversion. It is observed that polymerization rate experiments a rapid increase in the presence of more polar solvent water, and increasing in the content of H₂O results in an increase in the apparent rate constant of polymerization, and a decrease in the molecular weight distribution. The reaction rate and molecular weight increase along with the decrease of DMF content. The effect of Yb(0) powder content, different ligands and concentration of initiator on the polymerization is also investigated. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of main‐chain poly(carbazole)s via CuAAC

The synthesis and characterization of a novel family of main‐chain carbazole‐containing polymers using copper‐catalyzed azide‐alkyne cycloaddition chemistry is reported. The reactions were performed under mild conditions using readily available copper catalysts and ligands, which afforded polymeric products with M_ws up to 18 kDa. Using a range of techniques, the polymers were found to exhibit a glass transition temperature (T_g) of 85 °C, high thermal stability (T_d = 274 °C), and high photoluminescent quantum efficiency (?_f = 0.29; λ_em = 448 nm), which underscore their potential for use in organic light‐emitting diodes or other emissive devices, particularly where efficient blue emission is of value. The approach described offers practical advantages over other synthetic methods used to prepare main‐chain carbazole‐containing polymers, especially with regard to the lack of need for rigorously inert conditions and the absence of byproducts generated during the polymerization reaction. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Chiral crystal of a C2v‐symmetric 1,3‐diazaaulene derivative showing efficient optical second harmonic generation

Achiral nonlinear optical (NLO) chromophores 1,3‐diazaazulene derivatives, 2‐(4′‐aminophenyl)‐6‐nitro‐1,3‐diazaazulene (APNA) and 2‐(4′‐N,N‐diphenylaminophenyl)‐6‐nitro‐1,3‐diazaazulene (DPAPNA), were synthesized with high yield. Despite the moderate static first hyperpolarizabilities (β₀) for both APNA [(136 ± 5) × 10^?30 esu] and DPAPNA [(263 ± 20) × 10^?30 esu], only APNA crystal shows a powder efficiency of second harmonic generation (SHG) of 23 times that of urea. It is shown that the APNA crystallization driven cooperatively by the strong H‐bonding network and the dipolar electrostatic interactions falls into the noncentrosymmetric P2₁2₁2₁ space group, and that the helical supramolecular assembly is solely responsible for the efficient SHG response. To the contrary, the DPAPNA crystal with centrosymmetric P‐1 space group is packed with antiparalleling dimmers, and is therefore completely SHG‐inactive. 1,3‐Diazaazulene derivatives are suggested to be potent building blocks for SHG‐active chiral crystals, which are advantageous in high thermal stability, excellent near‐infrared transparency and high degree of designing flexibility. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Effect of particle agglomeration and interphase on the glass transition temperature of polymer nanocomposites

In this article, we utilize finite element modeling to investigate the effect of nanoparticle agglomeration on the glass transition temperature of polymer nanocomposites. The case of an attractive interaction between polymer and nanofiller is considered for which an interphase domain of gradient properties is developed. This model utilizes representative volume elements that are created and analyzed with varying degrees of nanoparticle clustering and length scale of interphase domain. The viscoelastic properties of the composites are studied using a statistical approach to account for variations due to the random nature of the microstructure. Results show that a monotonic increase in nanofiller clustering not only results in the loss of interphase volume but also obstructs the formation of a percolating interphase network in the nanocomposite. The combined impacts lead to a remarkable decrease of T_g enhancement of clustering nanofillers in comparison with a well‐dispersed configuration. Our simulation results provide qualitative support for experimental observations that clustering observed at high nanofiller concentrations negatively impacts the effects of the nanofiller on overall properties. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Hydrolytic Ring Opening Reactions of Pyromellitic Dianhydride for Divalent Transition Metal Carboxylate Complexes

The hydrolytic ring opening reactions of pyromellitic dianhydride is an effective method to prepare transition metal carboxylate complexes. In this paper, two dinuclear complexes [Ni₂(2,2′‐bipy)₂(btec)(H₂O)₆] · 2H₂O ( 1 ) and [Cd₂ (phen)₄(H₂O)₂(H₂btec)] · H₂btec · 2H₂O ( 2 ) (H₄btec = 1,2,4,5‐benzenetetracarboxylic acid, phen = 1,10‐phenanthroline, and 2,2′‐bipy = 2,2′‐bipyridine) were synthesized by slow diffusion methods and their structures were determined byX‐ray structure analysis. In both structures metal atoms are in distorted octahedral environments and they are linked by bis‐monodentately coordinated 1,2,4,5‐benzentetracarboxylate ligands as bridging units. The crystalline compounds, which are insoluble in water as well as common organic solvents, have been characterized in the solid‐state by elemental analysis, thermogravimetric analysis, IR, and diffuse reflectance UV/Visspectroscopy. Moreover, the study of the physical properties of complex 2 demonstrates that it exhibits blue fluorescence emission in the solid state at room temperature.     

New D-π-A dyes for efficient dye-sensitized solar cells

Functional organic dyes have promising prospect in dye-sensitized solar cells as a crucial element, of which sensitizers based on donor-π-acceptor are the most important dyes. On the basis of the structures of the aromatic amine donors such as triphenylamine and indoline, this paper reviews the photoelectric conversion properties of organic sensitizers since 2008, and highlights research work in our laboratory in this area.