Effect of main-chain rigidity on the phase transitional behavior of comblike polymers

The influence of the rigidity of polymer backbones on the side-chain crystallization and phase transition behavior was systematically investigated by a combination of differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), and high-resolution solid-state nuclear magnetic resonance spectroscopy (NMR). DSC investigation indicated that the crystallization number of alkyl carbon atoms of the side chains grafted onto the rigid polymer backbone, poly(p-benzamide) (PBA), is much lower than that of the alkyl carbon atoms of the side chains grafted onto the flexible polymer backbone, poly(ethyleneimine) (PEI), implying that the conformational state of the polymer backbones has a strong effect on the side-chain crystallization behavior in comblike polymers. WAXD and FTIR results proved that these two comblike polymers pack into hexagonal (PBA18C) and orthorhombic (PEI18C) crystals, respectively, depending on the adjusting ability of the polymer backbones for particular conformational states. It was also found that the presence of the crystalline-amorphous interphase (delta = 31.6 ppm) in PBA18C detected by solid-state C-13 NMR spectroscopy can be attributed to the rigid PBA backbone, which restricts the mobility of the alkyl side chains.

Synthesis and structural characterization of new tungsten(VI) complexes with polycarboxylate ligands

The reactions of (NH4)(2)WS4 and three polycarboxylate ligands {including nitrilotriacetate (nta(3-)), citrate (Hcit(3-)) and ethylenediaminetetra acetate (EDTA(4-))} in H2O/EtOH at ambient temperature have resulted in three new trioxotungsten (VI) complexes, K-3[WO3(nta)]center dot H2O 1, (NH4)(4)[WO3(cit)]center dot 2 H2O 2 and K-2(NH4)(2)[W2O6(EDTA)]center dot 4H(2)O 3, respectively. These three complexes have been characterized by IR, XPS, TGA-DTA, H-1 and C-13 NMR spectroscopy. And their structures have been determined by X-ray crystallographic studies, which confirm that I and 2 are mononuclear compounds and 3 is a binuclear compound. Each tungsten atom in 1-3 is coordinated to three unshared oxygen atoms, which adopt fac stereochemistry, while the remaining fac positions are occupied by three atoms from the ligands. The electrochemical properties of 2 and 3 have been investigated.

Facile syntheses and characterization of hyperbranched poly(ester-amide)s from commercially available aliphatic carboxylic anhydride and multihydroxyl primary amine

A new method for synthesis of novel hyperbranched poly(ester-amide)s from commercially available AA' and CBx type monomers has been developed on the basis of a series of model reactions. The hyperbranched poly(ester-amide)s with multihydroxyl end groups are prepared by thermal polycondensation of carboxyl anhydrides (AA') and multihydroxyl primary amine (CBx) without any catalyst and solvent. The reaction mechanism in the initial stage of polymerization was investigated with in situ H-1 NMR. In the initial stage of the reaction, primary amino groups of 2-amino-2-ethyl-1,3-propanediol (AEPO) or tris(hydroxymethyl)aminomethane (THAM) react rapidly with anhydride, forming an intermediate which can be considered as a new AB(x) type monomer. Further self-polycondensation reactions of the AB. molecules produce hyperbranched polymers. Analysis using H-1 and C-13 NMR spectroscopy revealed the degree of branching of the resulting polymers ranging from 0.36 to 0.55. These hyperbranched poly(ester-amide)s contain configurational isomers observed by C-13 and DEPT C-13 NMR spectroscopy, possess high molecular weights with broad distributions and display glass-transition temperatures (T(g)s) between 7 and 96 degreesC.

Synthesis and characterization of hyperbranched poly(ester-amide)s from commercially available dicarboxylic acids and multihydroxyl primary amines

A new method for syntheses of hyperbranched poly(ester-amide)s from commercially available A(2) and CBx type monomers has been developed on the basis of a series of model reactions. The aliphatic and semiaromatic hyperbranched poly(ester-amide)s with multihydroxyl end groups are prepared by in situ thermal polycondensation of intermediates obtained from dicarboxylic acids (A(2)) and multihydroxyl primary amines (CBx) in N,N-dimethylformamide. Analyses of FTIR, H-1 NMR, and C-13 NMR spectra revealed the structures of the polymers obtained. The MALDI-TOF MS of the polymers indicated that cyclization side reactions occurred during polymerization. The hyperbranched poly(ester-amide) s contain configurational isomers observed by C-13 and DEPT C-13 NMR spectroscopy. The DBs of the polymers were determined to be 0.38-0.62 by H-1 NMR or quantitive C-13 NMR and DEPT 135 spectra. These polymers exhibit moderate molecular weights, with broad distributions determined by size exclusion chromatography ( SEC), and possess excellent solubility in a variety of solvents such as N, N- dimethylacetamide, dimethyl sulfoxide, tetrahydrofuran, and ethanol, and display glass-transition temperatures (T(g)s) between -2.3 and 53.2 degrees C, determined by DSC measurements.

Synthesis and characterization of hyperbranched aromatic poly(ester-imide)s

The synthesis and characterization of hyperbranched aromatic poly(ester-imide)s are described. A variety of AB(2) monomers, N-[3- or 4-bis(4-acetoxyphenyl)toluoyl]-4-carboxyl-phthalimide and N-{3- or 4-[1,1-bis(4-acetooxyphenyl)]ethylphenyl}-4-carboxy phthalimides were prepared starting from condensation of nitrobenzaldehydes or nitroacetophenones with phenol and used for synthesis of hyperbranched poly(ester-imide)s containing terminal acetyl groups by transesterification reaction. These hyperbranched poly(ester-imide)s were produced with weight-average molecular weight of up to 6.87 g/mol. Analysis of H-1 NMR and C-13 NMR spectroscopy revealed the structure of the four hyperbranched poly(ester-imide)s. These hyperbranched poly(ester-imide)s exhibited excellent solubility in a variety of solvents such as N,N-dimethylacetamide, dimethyl sulfoxide, and tetrahydrofuran and showed glass-transition temperatures between 217 and 255 degreesC. The thermogravimetric analytic measurement revealed the decomposition temperature at 10% weight-loss temperature (T-d(10)) ranging from 365 to 416 degreesC in nitrogen.

Pentamethylcyclopentadienyl halfsandwich rhodium complexes containing 1,1 '-ferrocene dichalcogenido chelate ligands

The heterobimetallic complexes Cp * Rh(CN Bu-t)(EC5H4)(2)Fe [E = S(2),Se(3), Te(4)] have been synthesized by the reaction of halfsandwich rhodium complex Cp * Rh(CNtBu) Cl-2 with Fe(C5H4ELi)(2). 2THF. Oxidation of 2,3 by AgBF4 to give ferrocenium - type salts [Cp * Rh(CNtBu) (EC5H4)(2)Fe] (+) [BF4] (-) [E = S(5),Se(6)] also occurs readily. The new complexes have been characterized by MS IR, H-1 and C-13 NMR spectroscopy and elemental analysis.

Structure analysis of the fulvic acids extracted from composted corn stalk residue

Chemical structure of fulvic acids extracted from composted corn stalk residue(CSR FA)was studied by Fourier transform infrared (FTIR) spectroscopy, H-1 and C-13 nuclear magnetic resonance(H-1-NMR, C-13-NMR) spectroscopy. The results show that CSR FA mainly consists of four types of carbon: carbonyl, aromatical, alkyl and carbohydrate, the carbohydrate is dominant. Its aromaticity is 15.42%, less than that of CSR HA. This indicates that the construction of CSR FA is simpler than that of CSR HA, FA can not be extracted from undecomposed corn stalk residue. CSR FA may be formed by cellulose or hemicellulosemorties combined with aromatic compound from decomposed lignin.

Crystallization of syndiotactic polypropylene (sPP) from oriented melts

The influence of the syndiotacticity on the crystallization behaviour of syndiotactic polypropylene (sPP) has been investigated. The syndiotacticity has been measured by C-13-NMR spectroscopy and the phase formation has been observed by electron diffraction of oriented samples. It is shown that the crystal phase formation depends strongly on the perfection of the tacticity of the macromolecules.

Preparation and in vitro antioxidant activity of kappa-carrageenan oligosaccharides and their oversulfated, acetylated, and phosphorylated derivatives

In order to study the relationship between chemical structure and properties of modified carrageenans versus antioxidant activity in vitro, K-carrageenan oligosaccharides were prepared through mild hydrochloric acid hydrolysis of the polysaccharide, and these were used as starting materials for the partial synthesis of their oversulfated, acetylated, and phosphorylated derivatives. The structure and substitution pattern of the oligosaccharides and their derivatives were Studied using FTIR and C-13 NMR spectroscopy, and their in vitro antioxidant activities were investigated. Certain derivatives of the carrageenan oligosaccharides exhibited higher antioxidant activity than the polysaccharides and oligosaccharides in certain antioxidant systems. The oversulfated and acetylated derivatives, which scavenge superoxide radicals, the phosphorylated and low-DS acetylated derivatives, which scavenge hydroxyl radicals, and the phosphorylated derivatives, which scavenge DPPH radicals, all exhibited significant antioxidant activities it, the systems examined. The effect of the molecular weight of the carrageenan on antioxidant activities, however, is not obvious from these studies. (c) 2005 Elsevier Ltd. All rights reserved.

Antimicrobial activity of hydroxylbenzenesulfonailides derivatives of chitosan, chitosan sulfates and carboxymethyl chitosan

Chitosan, carboxymethyl chitosan (CIVICS) and chitosan sulfates (CSS) with different molecular weight were modified by reacting with 4-hydroxyl-5-chloride-1,3-benzene-disulfo-chloride or 2-hydroxyl-5-chloride-1,3 -benzene-disulfo-chloride to give 12 kinds of new hydroxylbenzenesulfonailides derivatives of them. The preparation conditions of the derivatives were discussed in this paper, and their structures were characterized by FT-IR and C-13 NMR spectroscopy. The solubility of the derivatives was measured in the experiment. In addition, their antimicrobial activities against four bacteria and five crop-threatening pathogenic fungi were tested in the experiment. Besides, the rule and mechanism of their antibacterial activities were discussed in this paper. (C) 2009 Published by Elsevier B.V.

The antioxidant activity of 2-(4(or 2)-hydroxyl-5-chloride-1,3-benzene-di-sulfanimide)-chitosan

Chitosan (CS) with two different molecular weights was modified by reacting with 4-hydroxyl-5-chloride-1,3-benzene-disulfo-chloride or 2-hydroxyl-5-chloride-1,3-benzene-disulfo-chloride to give new 2-(4(or 2)-hydroxyl-5-chloride-1,3-benzene-di-sulfanimide)-chitosan (2-HCBSAHCS, 2-HCBSALCS, 4-HCBSAHCS, 4-HCBSALCS). The structure of the derivatives was characterized by FT-IR and C-13 NMR spectroscopy. The antioxidant activities of the derivatives were investigated employing various established systems, such as hydroxyl radical ((OH)-O-center dot)/superoxide anion (O-2(radical anion)) scavenging/reducing power and chelating activity. All the derivatives showed stronger scavenging activity on hydroxyl radical than chitosan and ascorbic acid (Vc), and IC50 of 4-HCBSAHCS, 4-HCBSALCS, 2-HCBSAHCS and 2-HCBSALCS was 0.334, 0.302, 0.442, 0.346 mg/mL, respectively. The inhibitory activities of the derivatives toward superoxide radical by the PMS-NADH system were strong. The results showed that the superoxide radical scavenging effect of 2-(4(or 2)-hydroxyl-5-chloride-1,3-benzene-disulfanimide)-chitosan was higher than chitosan. The derivatives had obviously reducing power and slight chelating activity. The data obtained in in vitro models clearly establish the antioxidant potency of 2-(4(or 2)-hydroxyl-5-chloride-1,3-benzene-disulfanimide)-chitosan. (C) 2007 Elsevier Masson SAS. All rights reserved.

Dramatic solvent effects on ring-opening metathesis polymerization of cycloalkenes

A series of metathesis polymers and copolymers have been formed and their structures were analysed by C-13 NMR spectroscopy. Noble metal and non-noble metal salt catalysts are distinguished by their behaviour in various solvents. Thus, in phenolic solvents, the former class produce alternating copolymers from cyclopentene and norbornene, while the latter are unaffected and produce random copolymers. In contrast, ether solvents have the effect of markedly increasing the cis content of polymers from the latter catalysts while the former are unaffected.

CO2 Capture in Wet and Dry Superbase Ionic Liquids

The solubility of carbon dioxide in five tetraalkylphosphonium superbase ionic liquids, namely the trihexyltetradecylphoshonium phenoxide, trihexyltetradecylphoshonium benzotriazolide, trihexyltetradecylphoshonium benzimidazolide, trihexyltetradecylphoshonium 1,2,3-triazolide, and trihexyltetradecylphoshonium 1,2,4-triazolide was studied experimentally under dry and wet conditions at 22 A degrees C and at atmospheric pressure, using a gravimetric saturation technique. The effects of anion structure and of the presence or absence of water in the solution on the carbon dioxide solubility were then deduced from the data. H-1 and C-13-NMR spectroscopy and ab initio calculations were also conducted to probe the interactions in these solutions, as carbon dioxide and water can compete in the ionic liquid structure during the absorption process. Additionally, the viscosity of selected superbase ionic liquids was measured under dry and wet conditions, in the presence or absence of CO2, to evaluate their practical application in carbon dioxide capture processes. Finally, the recyclability of the trihexyltetradecylphoshonium 1,2,4-triazolide under dry and wet conditions was determined to probe the ability of selected solvents to solubilize chemically a high concentration of carbon dioxide and then release it in a low energy demand process.

Aza-annulation of enaminones with itaconic anhydride:kinetic preference for exocyclic enamide products

Enaminones react with itaconic anhydride in methylene chloride at room temperature to give exocyclic enamides sis the major products. These can be readily equilibrated to the thermodynamically more stable endocyclic enamides. In substrates where the exocyclic isomer could not be formed only intractable materials were produced from this reaction. An intermediate in this two step process was detected and identified by proton and C-13 NMR spectroscopy. In two cases chiral enaminones were employed and the relative stereochemistry at the new chiral centre in the product was established by a crystal structure of compound 27.

Liming upland grassland: the effects on earthworm communities and the chemical characteristics of carbon in casts

Different earthworm species have different tolerances of acid soil conditions, and the application of lime to upland grassland to improve the grazing quality may therefore alter the size and diversity of the earthworm community. Altering soil properties may also affect the chemical characteristics of organic C in earthworm casts. We surveyed the earthworm community of an upland grassland in southern Scotland at the outset of annual lime applications, and after 3 years, and used C-13 nuclear magnetic resonance (NMR) spectroscopy to assess the distribution of C between different functional groups in the organic matter. In addition, soil was incubated for 8 weeks with several earthworm species in the presence or absence of lime, and the earthworm casts were subsequently analysed by C-13 NMR spectroscopy. Liming did not significantly affect earthworm abundance or species diversity, but it did affect the chemical composition of the casts. Casts from earthworms incubated in unlimed soil had greater ratios of alkyl-C to O-alkyl-C, indicative of more decomposed, recalcitrant C, and spectra from litter-feeding species had the greatest intensities of O-alkyl-C signals. In limed soil, the largest O-alkyl-C signal intensities were not restricted to litter-feeding species, indicating an increase in the quality of organic matter ingested by geophagous species.