Synthesis,characterization, and curing of hyperbranched allyl ether–maleate functional ester resins

A model two-step synthesis of a saturated hyperbranched hydroxyl-terminated ester has been developed to show a synthesis route. Three different series of hyperbranched esters with different terminations have been synthesized to relate some of their properties to their structures. This route has then been used to synthesize three different allyl ethermaleate functional hyperbranched ester resins in a two-step procedure. The resins have been characterized with respect to rheology, structure, and properties, and the differences are discussed. The allyl ether-maleate functional resins have also been studied with respect to curing performance and final film properties. © 1993 John Wiley & Sons, Inc.     

Crosslinked polystyrene with improved mechanical properties

The synthesis of some divinyl monomers—bis(vinylphenyl)ethane ( 2 ), bis(vinylbenzyloxy)hexane ( 3a ), and bis(vinylbenzyloxy)dodecane ( 3b ) is reported. Copolymers of the new monomers and styrene were evaluated as an alternative to divinylbenzene-crosslinked polymers for use as matrices and absorbents. The mechanical properties and the amount of residual double bonds in the copolymers were compared. It was found that the new copolymers, unlike the divinylbenzene-crosslinked polymers, retained their mechanical strength even at high crosslinking degrees. Stress at break values of 79, 68, and 18 N/mm² were found for the polymers crosslinked with 20 mol % of 3a, 2 , and divinylbenzene; 5, 25 and 45% of the divinyl units in these polymers were left as pendant double bonds. Porous styrene– 2 copolymers were synthesized and shown to have lower surface areas than the corresponding divinylbenzene-crosslinked polymers. The pore size distribution showed that this was due to the absence of the smallest pores which are found in the divinylbenzene-crosslinked polymers in between heavily crosslinked nodules. © 1993 John Wiley & Sons, Inc.     

Solvent effects on the redox properties of Cu complexes used as mediators in atom transfer radical polymerization

Solvent effects on the redox properties of six Cu(I) complexes used as mediators in atom transfer radical polymerization (ATRP) have been studied using cyclic voltammetry. The six ligands used were tris[2-(dimethylamino)ethyl]amine, N-(n-propyl)-2-pyridylmethanimine, N,N,N',N',N'-pentamethyldiethylenetriamine, 1,1,4,7,10,10-hexamethyl-triethylenetetramine, 2,2'-bipyridine, and 1,4,8,11-tetraaza-1,4,8,11-tetramethylcyclotetradecan. The solvents used were DMSO, DMF, MeCN, MeOH, IP, and BuOH. Significant solvent effects were observed and quantitatively analyzed in terms of Kamlet-Taft relationships. The resulting Kamlet-Taft equations were found to successfully describe the solvent effects and could thus be used as tools for the design of ATRP in new solvents. The solvent sensitivity of the different ligands and the nature of the solvent effects are also discussed to some extent.     

ESI-MS detection of proposed reaction intermediates in the air-promoted and ligand-modulated oxidative Heck reaction

Electrospray ionization mass spectrometry (ESI-MS) and subsequent MS/MS analyses were used to directly detect palladium-containing cationic reaction intermediates in a ligand controlled palladium(II)-catalyzed oxidative Heck arylation. All potential intermediates were observed as dmphen-ligated palladium(II) species, suggesting that the dmphen bidentate ligand is attached to the metal center during the entire catalytic cycle. The study supports previous mechanistic propositions and provides new information regarding the composition of aryl-containing Pd(II) complexes in an ongoing oxidative Heck reaction. In addition, sodium acetate was found to be a useful base alternative to previously used tertiary amines.     

A thermally stable Pt/Y-based metal-organic framework: Exploring the accessibility of the metal centers with spectroscopic methods using H2O, CH3OH, and CH3CN as probes

A metal-organic framework (MOF) based on Pt, Y, and 2,2'-bipyridine-5,5'-dicarboxylate (BPDC), stable up to 400 degrees C, has been synthesized and characterized. In this MOF, the Pt centers are coordinated to Cl and the N atoms of the BPDC unit, giving a local environment similar to that found in a series of Pt-organic complexes with catalytic activity toward C-H bond cleavage of alkanes. This new material is a heterogeneous counterpart to the corresponding metal-organic complex. The structure, determined by single-crystal XRD data, is the repetition of three covalently bonded layers. These layers form a block, which is stacking as an (a)(b)(c) sequence along the crystallographic b-axis. Each layer contains the Pt-organic unit, while Y atoms represent the connection between adjacent layers. No covalent connection is present between layer (a) of a block and layer (c) of an adjacent block. EXAFS (BM29 at the ESRF) analysis supports the XRD data. As this MOF crystallizes under hydrothermal conditions, water acts both as solvent and as a direct ligand of Y. Accessibility to the metal centers is demonstrated by reversible water desorption/readsorption, as determined by TPA/TPD, FTIR, UV-vis, EXAFS, and XANES. Importantly, the results show that the as-synthesized material will not suffer a permanent loss in porosity upon solvent removal. In addition to water, methanol, ethanol, and acetonitrile can also access the internal void of the dehydrated phase.     

Synthesis, crystal structure and magnetic properties of the open framework compound Co3Te2O2(PO4)2(OH)4

The new compound Co₃Te₂O₂(PO₄)₂(OH)₄ was synthesized using hydrothermal techniques. It crystallizes in the monoclinic space group C2/m with the unit cell a=19.4317(10) Å, b=6.0249(3) Å, c=4.7788(2) Å, β=103.139(5)°. The crystal structure is an open framework having chains of edge sharing [Co(1)O₆] octahedra. Other building blocks are [TeO₃(OH)₂], [PO₄] and [Co(₂)O₂(OH)₄] connected mainly via corner sharing. The –OH groups protrude into channels in the structure. The magnetic susceptibility measured from 2 to 300 K shows two broad anomalies at around 21 K and 4 K, respectively. The peak at ∼20 K is ascribed to a two-dimensional antiferromagnetic ordering of linear [Co(1)O₆] chains coupled by interchain interaction via [PO₄] groups in the Co(1) sheets. The second transition at 4 K is ascribed to a second antiferromagnetic ordering of the moments of the Co(2) entities via super–super exchange involving [PO₄] and [TeO₃(OH)₂] groups. This assignment is strongly supported by low-temperature heat capacity measurements indicating an entropy removal within the high-temperature transition of about twice the magnitude of the low-temperature transition.     

Multicomponent analysis of drinking water by a voltammetric electronic tongue

A voltammetric electronic tongue is described that was used for multicomponent analysis of drinking water. Measurements were performed on drinking water from a tap and injections of the compounds NaCl, NaN₃, NaHSO₃, ascorbic acid, NaOCl and yeast suspensions could be identified by use of principal component analysis (PCA). A model based on partial least square (PLS) was developed for the simultaneously prediction of identification and concentration of the compounds NaCl, NaHSO₃ and NaOCl. By utilizing this type of non-selective sensor technique for water quality surveillance, it will be feasible to detect a plurality of events without the need of a specific sensor for each type of event.     

Contribution from a hole-conducting dye to the photocurrent in solid-state dye-sensitized solar cells

The hole transporting medium in solid-state dye-sensitized solar cells can be utilized to harvest sunlight. Herein we demonstrate that a triphenylamine-based dye, used as hole-transporting medium, contributes to the photocurrent in a squaraine-sensitized solid-state dye-sensitized solar cell. Steady-state photoluminescence measurements have been used to distinguish between electron transfer and energy transfer processes leading to energy conversion upon light absorption in the hole-transporting dye.