Synthesis and characterization of ABn-type α-cyclodextrin monomer and its hyperbranched polymer

To obtain well-defined structures of α-cyclodextrin (α-CD) based monomer and its hyperbranehed polymer (HBP), a modified α-CD molecule with one electron-rich alkene and many electron-poor acrylates was first prepared through the esterification reaction between mono-ester undecylenic acid-α-CD and acrylic acid. It was then utilized as an AB_n-type monomer for subsequent ADMET polymerization between alkene and acrylate using the second generation Hoveyda-Grubbs catalyst in homogeneous water/organic [D₂O/(CD₃)₂CO] mixtures via acyclic diene metathesis (ADMET) polymerization. A novel cyclodextrin-based HBP was obtained in prolonged reaction time. The monomer and HBP were characterized by NMR, elemental analysis, FTIR, and MALDI-TOF MS measurements. It was found that the actual molecular structures of both monomer and polymer were identical with the designed structures. The produced polymers have molecular weights within 13.2 and 56.3 kDa, and their polydispersity indices range from 2.78 to 2.63 by multiangle laser light scattering-gel permeation chromatography. The degree of branching was determined by ¹H NMR spectroscopy and the values ranges from 0.41 to 0.52.     

Synthesis and characterization of novel crown ether containg copolymers Ru catalyzed copolymerization of 4′-acetylbenzocrown ethers with α,ω-dienes

Summary Ruthenium catalyzed step growth copolymerization of 4-acetylbenzo-15-crown-5 and 4-acetylbenzo-18-crown-6 and ,-dienes such as 1,3-divinyltetramethyldisiloxane or 3,3,6,6-tetramethyl-3,6-disila-1,7-octadiene give novel copolymers which incorporate crown ethers into the polymer backbone in a regular manner. The synthesis of these thermally stable copolymers and their characterization is reported. Lithium cation crown complexes have been formed.     

Cyclic poly(dimethylsiloxane) via ring-closing dehydrocoupling of α,ω-dihydroxy-PDMS with α,ω-dihydrido-PDMS in dilute solution

Cyclic poly(dimethylsiloxane) (PDMS) was prepared from commercially available linear α,ω-dihydroxy-PDMS by a platinum-catalyzed dehydrocoupling of its chain ends with α,ω-dihydrido-PDMS in dilute solution. Ring closing was verified by MALDI-ToF mass spectrometry along with GPC, IR, ¹H and ²⁹Si NMR spectroscopy. Purification of the cyclic PDMS was achieved by inclusion complexation of linear byproducts with γ-cyclodextrin. Cyclic yields are ≥ 50% and the average molecular weight (M) closely reflects that of the linear starting material. Yields of large cycles, [(CH₃)₂SiO]_x where x > 6, are greater than those achieved by the traditional ring-chain equilibration route beginning with [(CH₃)₂SiO]₄ and [(CH₃)₂SiO]₅[1], and the M is greater than that obtained for the cyclic product obtained from base-catalyzed cyclodepolymerization of the same α,ω-dihydroxy-PDMS precursor [2].     

Synthesis,characterization, and magnetic properties of α-MnS nanocrystals

MnS nanocrystals have been prepared by a colloidal synthesis route through the reaction of MnCl₂ and S[Si(CH₃)₃]₂ in trioctylphosphineoxide. The nanocrystals were characterized using X-ray diffraction and transmission electron microscopy. The magnetic properties were studied with SQUID magnetometry. X-ray diffraction shows that the nanocrystals are of the thermodynamically stable α-MnS (alabandite) structure. Size control was achieved by changing the concentration of the precursors. Nanocrystal sizes were measured by transmission electron microscopy, and three samples of average diameters 20, 40, and 80 nm were obtained, with narrow size distribution (σ˜9%). The zero field cooled magnetization curves for the 80-, 40-, and 20-nm samples showed a cusp at 116 K, 97 K, and 50 K respectively, all smaller than the antiferromagnetic transition temperature, T_N = 130 K, of bulk α-MnS. Below T_N the magnetization exhibits a paramagnetic behavior unlike typical antiferromagnetic materials. These results indicate that there is a mixture of paramagnetic and antiferromagnetic phases in the nanocrystals. The size dependence shows a general trend of decrease of T_N with reduced particle size, indicating size dependent magnetic ordering.     

Synthesis and investigation of α,ω-methacryloyl terminated epoxide-amine macromonomers

Summary ,-methacryloyl-poly (epoxide-amine)-macromonomers were synthesized by reaction of bisphenol-A diglycidylether DGEBA and methacrylic acid followed by addition polymerization of unreacted expoxide groups with primary monoamines or disecondary diamines, respectively. The resultant macromonomers having M_n (vpo)-values between 530 and 2000 g/mol were analysed by IR-, ¹H-NMR- and ¹³C-NMR-spectroscopy. HPLC and GPC analysis were used to determine the distribution of oligomers. The macromonomers are glassy or viscous liquids with T_g between 0 and 50 °C depending on the nature of the amine and polymerization degree.     

Ruthenium catalyzed copolymerization of 2-acetylphenanthrene and α,ω-dienes

Summary Copolymers with 2-aceto-1,3-phenanthrenylene units in the chain have been directly prepared by Ru catalyzed step-growth copolymerization of 2-acetyl phenanthrene and ,-dienes such as 1,3-divinyltetramethyldisiloxane. Copolymers which incorporate 2-aceto-1,3-phenanthrenylene units possess higher T_gS and increased thermal stability compared to analogous copolymers which have 2-aceto-5-phenyl-1,3-phenylene(biphenyl) or 2-aceto-1,3-phenylene units. Fluorescence spectra of these copolymers have been obtained.     

Ruthenium catalyzed regioselective copolymerization of acetophenone and α,ω-dienes

Summary This paper reports a novel ruthenium catalyzed regioselective copolymerization reaction between acetophenone and ,-dienes such as divinyltetramethyldisiloxane and divinyldimethylsilane which leads respectively to copoly(3,3,5,5-tetramethyl-4-oxa-3,5-disila-1,7-heptanylene/2-acetyl-1,3-phenylene) and copoly(3,3-dimethyl-3-sila-1,5-pentanylene/2-acetyl-1,3-phenylene). This reaction involves the ruthenium catalyzed insertion of the carbon-carbon double bonds of ,-dienes into the aromatic C–H bondsortho to the acetyl group of acetophenone. Similar ruthenium catalyzed reactions between acetophenone and alkenes to yield monomericortho alkyl substituted acetophenones have been recently reported.¹     

Ruthenium catalyzed regioselective copolymerization of anthrone,fluorenone, or xanthone with α,ω-dienes

Summary This paper reports a novel ruthenium catalyzed regioselective copolymerization reaction between anthrone, fluorenone or xanthone and ,-dienes such as 1,3-divinyltetramethyldisiloxane and 3,3,6,6-tetramethyl-3,6-disila-1,7-octadiene. This reaction involves the ruthenium catalyzed regioselective Anti-Markovnikov insertion of the carbon-carbon double bonds of the ,-dienes into the aromatic carbon-hydrogen bonds which are ortho to the carbonyl group of anthrone, fluorenone or xanthone. Similar ruthenium catalyzed copolymerization reactions between acetophenone and ,-dienes [1] have been recently reported as have reactions between acetophenone and alkenes to yield monomeric ortho-alkyl substituted acetophenones [2].     

Synthesis and characterization of quaternized poly-alkyl α-chloroacetoxymethacrylates

Summary The homopolymers of ethyl α-chloroacetoxymethacrylate (ECAM) and t-butyl α-chloroacetoxymethacrylate (TBCAM) were quaternized homogeneously with trimethylamine (TMA) and N,N-dimethyldodecylamine in N,N-dimethylformamide (DMF). The ¹H-NMR measurments were used for the determination of the degree of quaternization (DQ) values. The DQ value of poly-ECAM quaternized with TMA at room temperature after 1 h was found to be 84 %, while the DQ value for poly-ECAM quaternized with N,N-dimethyldodecylamine was 37 %. Reactivity of poly-TBCAM was lower than that of poly-ECAM. The lower DQ value of TMA quaternized poly-TBCAM (19 %) is caused by steric hindrance in the vicinity of - CH₂Cl group due to bulky t-butyl group. Increasing reaction time, polymer concentration and temperature above a certain value for each polymer, resulted in crosslinked polymers. Solubility of the quaternized polymers is controlled by the substituents. Thermogravimetric analysis showed distinct differences in thermal stabilities which is controlled by the quaternary amine groups and ester substituents. Received: 19 February 2000/Revised version: 14 April 2000/Accepted: 14 April 2000     

Synthesis and self-assembling properties of α,ω-hydroxy-poly(ethylene oxide) end-capped with 1-isocyanato-3-pentadecylcyclohexane

A novel hydrophobic compound, 1-isocyanato-3-pentadecylcyclohexane (PDC) issued from a renewable resource material (Cashew Nut Shell Liquid), is used to end-cap poly(ethylene oxide) (PEO) of different molecular weights. The synthesis, characterization and self-assembling properties of these new associating polymers are reported. In aqueous solution, PDC modified PEOs self-associate into micellar structures which are characterized by neutron scattering. Using a star-polymer model with sticky hard sphere interactions, it is shown that the characteristics of the micelles mainly depend on the size of the PEO chain. In the case of PDC stickers, the aggregation number decreases from 25 to 17 with increasing molecular weight of PEO, from 10 to 20 kg/mol, respectively. The temperature directly impacts the interaction potential between the hydrophilic coronas of PEO which become less repulsive with increasing temperature. Rheological measurements, performed in dilute solution, clearly demonstrate that PEO micelles self-associate into open supramolecular structures. The correlation length of these loose clusters increases with polymer concentration and the hierarchical self-assembly follows the rules of the percolation theory. The sol/gel transition takes place at the overlap concentration of clusters. In semi-dilute solution, the viscoelastic properties of PDC end-capped PEOs are well described by the Maxwell model with a single relaxation mode. The characteristic time of the network follows an Arrhenius temperature dependence with an activation energy of 70 kJ/mol, in very good agreement with the size of PDC stickers.     

Comparison of aliphatic polyesters prepared by acyclic diene metathesis and thiol-ene polymerization of α,ω-polyenes arising from oleic acid-based 9-decen-1-ol

Development of more sustainable and environmentally friendly polymers as alternatives to petroleum-based polymers is a priority. We report the synthesis of six linear, aliphatic, renewable polymers by acyclic diene metathesis (ADMET) and thiol-ene polymerization of α,ω-polyenes resulting from thermal esterification of adipic, azelaic, and itaconic acids with 9-decen-1-ol. ADMET homopolymerization was performed with 1.0 mol% Hoveyda–Grubbs second generation metathesis catalyst. Thiol-ene copolymerization was conducted photochemically with 1 wt% 2,2-dimethoxy-2-phenyl-acetophenone and stoichiometric 1,2-ethanedithiol (EDT). Although the thiol-ene copolymers exhibited carbon and atom economies of 100%, the ADMET-derived polyesters possessed superior renewable carbon content (100%) and environmental factors (<4). These results were attributed to incorporation of non-renewable EDT into poly(thioether-ester)s and loss of ethene during production of ADMET polyesters. The M_n (>26 kDa), M_w (>92 kDa), and dispersities (>3.4) of the poly(thioether-ester)s were higher than the corresponding polyesters, which in part explained why the poly(thioether-ester)s gave higher melting (>61°C), crystallization (>49°C) and glass transition (>−31°C) temperatures. The cross-linked itaconate polymers did not melt or crystallize, thereby suggesting amorphous morphology. Lastly, the ADMET polyesters were more thermally stable (T₅₀ > 408°C) than the poly(thioether-ester)s (T₅₀ < 377°C). In summary, the aliphatic biopolymers displayed a wide range of properties that were impacted by polymerization method as well as the nature of the monomer.     

Synthesis,characterization and controlled release behaviour of adducts from chloroacetylated cellulose and α-naphthylacetic acid

Celluloses partially functionalized with chloroacetate groups were obtained by reaction of cellulose with chloroacetyl chloride using pyridine as catalyst and the dimethylacetamide/LiCl system as solvent. ¹³C NMR spectra at 75.4 MHz of partially modified cellulose with chloroacetate groups were studied in order to evaluate the selectivity of the reaction of cellulose with chloroacetyl chloride in the homogeneous phase. Analysis of the spectra of ring carbons in the anhydroglucose units shows that the reactivity of the individual hydroxyl groups decreases in the order C-6>C-3>C-2. The coupling of α-naphthylacetic acid to cellulose functionalized with chloroacetate groups was carried out by reaction with their potassium salts or directly in the presence of 1.8-diazabicyclo[5.4.0]-7-undecene. High degrees of modification were obtained by both methods. However, the esterification reaction is somewhat more efficient in the case of the potassium salt. The kinetic results were consistent with a second-order reaction. The hydrolysis in the heterogeneous phase of cellulose–α-naphthylacetic acid adducts showed that the release of the bioactive compound is dependent on the hydrophilic character of the adduct as well as on the pH value of the medium.     

Nanocomposites prepared with NR and solid-state organic modified montmorillonite

固相法改性蒙脱土及其在天然橡胶中的应用孙玉海,罗远芳,贾德民,傅伟文(华南理工大学材料科学与工程学院,广东广州510640)用丙烯酰胺作改性剂,采用固相法对蒙脱土进行有机改性,用改性的蒙脱土通过机械共混制备了橡胶/蒙脱土纳米复合材料,并将混炼胶在硫化前进行了适当的热处理以提高插层效果。抽提后蒙脱土的红外图谱显示改性剂和蒙脱土之间形成了牢固的化学键合。X射线分析表明改性剂使蒙脱土的层间距由1.52 nm增大到1.88 nm,热处理前后硫化胶中蒙脱土的层间距分别达到了4.19 nm和4.41 nm。     

Combustion synthesis and characterization of spherical α-MnMoO4 nanoparticles

In this study, α-MnMoO₄ nanoparticles were prepared by combustion synthesis method. The structural, morphological and electrical characteristics of α-MnMoO₄ were investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, transmission electron microscopy and impedance spectroscopy. The structural parameters were calculated from XRD pattern which confirmed the monoclinic structure of α-MnMoO₄. FT-IR and Raman spectroscopy results revealed the presence of MoO₄ surface functional groups. The TEM and HRTEM investigations evidenced the presence of homogeneous distribution of spherical nanoparticles and high crystallinity of α-MnMoO₄. Moreover, the SAED patterns clearly revealed the polycrystalline nature of the material. The conductivity measurements had inferred the semiconducting property of α-MnMoO₄ and the maximum conductivity of 1.94 × 10^? 6 S/cm was attained at 540 °C.     

Isolation of an active peptide fragment from human serum albumin and its synergism with α-tocopherol

An active peptide was isolated from hydrolysates of human serum albumin. This peptide was initially isolated by gel permeation chromatography and subsequent reversed-phase high-performance liquid chromatography. This active peptide, composed of 10 amino acid residues, was further hydrolyzed with a lysyl endopeptidase to give two peptide fragments. Only one fragment, identified as the tetrapeptide Leu-Gln-His-Lys, was found to have activity comparable to the original peptide and corresponded to the amino acid residues 103–106 of human serum albumin. Among these four amino acid residues, the His-Lys sequence seemed to be important in the occurrence of potent activity by comparison of the structural similarity with another active tetrapeptide, Asp-Thr-His-Lys, which had been previously isolated from bovine serum albumin hydrolysates. In addition, the active fragment showed potent synergism by preventing consumption of α-tocopherol during the autoxidation of linoleic acid.