扩链法合成赖氨酸改性聚乳酸的研究

以D,L-丙交酯为原料,辛酸亚锡为催化剂,赖氨酸为引发剂,丙交酯开环聚合制备双端羟基聚乳酸（HO-PLA-Lys-PLA-OH）寡聚体,经16,-六亚甲基二异氰酸酯（HDI）扩链获得赖氨酸改性的聚乳酸材料。用傅里叶红外光谱、核磁共振、接触角、粘度法等手段对赖氨酸改性聚乳酸结构和性能等进行了表征。结果表明：赖氨酸可以引发丙交酯聚合,产物为含赖氨酸的双端羟基聚乳酸寡聚体;扩链产物的粘均分子量是寡聚体的3.6倍,其接触角变大,亲水性降低。     

Spontaneous formation and transformation of organic free radical cations upon adsorption of olefins on H-mordenite

The radical cation of 2,5-dimethyl-2,4-hexadiene is identified by ESR upon adsorption of the parent molecule on activated H-mordenite. The same radical is observed when 2,3-dimethyl-1-butene or 2-methylpropene is adsorbed. This is clear evidence for highly specific dimerisation-fragmentation reactions of the primary radical cations in the zeolite at room temperature.     

Toward the Rational Design of Conjugated Oligomers and Polymers: Systematic Study of the Substituent Effect in Oligothiophenes

A systematic study of substituent electronic effects on a number of oligothiophene properties was performed using well-defined oligothiophenes of various chain lengths that were monosubstituted with classical electron-withdrawing or -donating groups. The main focus was to understand how the effect of a substituent on one thiophene ring was transmitted through the other thiophene rings in the oligomer. The physical and electrochemical properties were studied by optical absorption and emission spectroscopy and by cyclic voltammetry. The experimental data were complemented with theoretical calculations of HOMO LUMO gaps, charge distribution, bond length alternations, and ¹³C NMR spectra. We show that substitution has a significant electronic effect on the substituted ring; however, the effect decreases strongly over conjugation. A semiquantitative evaluation of the substituent effect in a well-defined long conjugated system was obtained for the first time using the Hammett equation.     

The electrochemical oxidation of phenylenediamines

Five p-phenylenediamines were oxidized electrochemically at a glassy carbon rotating ring-disk-electrode assembly. The overall reaction comprises the transfer of two electrons per molecule. At low to intermediate potentials the rate determining step for all the five compounds is the acid dissociation of the semiquinonediimine radical cation formed in a pre-equilibrium involving the transfer of one electron. Only at higher potentials can the radical cation be oxidized in parallel to the neutral semiquinone radical to form the quinonediimines. In contrast, the neutral semiquinonediimine radicals are oxidized at the same or even a lower potential than the parent phenylenediamines. The dissociation rate constants of the radical cations are in the range of 10-300 s⁻¹. The effect of the substituents on the oxidation potentials is as expected by their property to donate electrons to the mesomeric system. Their effect on the dissociation rates, however, seems to rather correlate with the inductive effect and might influence not only the electronic structure of the molecule itself but also the structure of the ions and the solvent around them. The semiquinonediimine radical cations are found to be slightly more acidic than their protonated parent phenylenediamine cations with pK_a values somewhat below 6.     

Electrochemical synthesis of polymers with alternate phenothiazine and bithiophene units

An electrochemical and spectroelectrochemical study of a new monomer—N-alkyl-bis(thiophene)phenotiazine have been presented. Electrochemical polymerization of the monomer leads to a polymer with alternate phenothiazine and bithiophene units. Polymerization proceeds after bielectronic oxidation of the molecule. Monoelectronic oxidation gives a stable radical cation with spin located on phenothiazine. Electrochemical properties of the polymer depend on the thickness of the film deposited on the electrode. For thin layers one can observe a characteristic redox couple of phenothiazine oxidation to a radical cation. Analysis of the polymer behaviour and the results of spectroelectrochemical measurements indicate a mixed-type of polymer conductivity.     

Arene—onium cations—VI Electrode kinetics of the anodic formation of arene—sulphonium cations from bisarenesulphides

Electrode kinetic investigations (voltammetry at stationary electrodes, rotating ring—disc electrodes and rotating rod electrodes) of the anodic oxidation of bisanisole-, bismesitylene-, bisxylene-, bistoluene- and bisbenzenesulphide were performed in acetonitrile. Observed anodic half wave potentials increase in the given order. The S-radical cations of the bisarenesulphides form in a reversible one-electron oxidation step. The radical cations of bisanisole- and bismesitylenesulphide are unable to react, even with relatively strong bases like water, and they disproportionate to form the more reactive dications which react readily with different nucleophiles. The more reactive radical cations of bisxylene-, bistoluene- and bisbenzenesulphide react directly with nucleophiles, for instance with aromatic bases and with the more basic hydrocarbons (anisole, styrene). Participation of dications in their consecutive reactions cannot be detected. The anodic dimerization of these three bisarenesulphides is a relatively fast reaction and is due to the addition of the respective bisarenesulphide radical cation to bisarenesulphide molecules. The reason for the striking mechanistic difference for the two groups of radical cations is very likely an unfavourable disproportionation equilibrium for the more reaction bisarenesulphide radical cations.     

Electrochemical and UV–Vis/ESR spectroelectrochemical properties of thienylenevinylenes substituted by a 4-cyanostyryl group

The π-electron delocalisation in conjugated thienylenevinylenes bearing arylethenyl chromophores, makes those materials interesting candidates for electro-optic applications. In this study, we report the results of electrochemical and UV–Vis/ESR spectroelectrochemical studies of a pair of thienylenevinylenes substituted by the 4-cyanostyryl group, bearing either a hydrogen, or methyl group terminated α carbons at the peripheral thiophene rings. The reactivity of various functional segments of investigated molecules was assessed by comparing the reactivity of the protected and unprotected counterparts and the behaviour of their electrooxidation products. For the capped derivative, two irreversible anodic redox processes giving electrochemically inactive products were observed, while the uncapped molecule yields electroactive materials already upon its first oxidation step.     

A study on the electro-oxidation and electropolymerization of a new OPE linear molecule by EQCM and in situ FTIR spectroelectrochemistry

A novel symmetric conjugated oligo(phenylene-ethynylene) (OPE) linear molecule (1,4-bis(4-aminophenylethynyl)benzene); BAB) was synthesized by Sonogashira cross-coupling reactions. The structure and purity of the compound were confirmed by ¹H NMR, ¹³C NMR and infrared (IR) and mass spectrometry (MS). The electrochemical oxidation process and mechanism of BAB were investigated via in situ Fourier transform infrared (FTIR) spectroelectrochemistry and electrochemical quartz crystal microbalance (EQCM). The electrochemical oxidation mechanism of BAB was proposed. The studies revealed that the BAB concentration and oxidation potential had a significant influence on the growth of the polymer film. A densely packed polymer film, which exhibited nonelectroactivity, was formed when a high monomer concentration and a high oxidation potential were used. When the electropolymerization of BAB was conducted at a lower concentration, a new pair of redox peaks appeared, and the resultant thin film had better electroactivity. The in situ FTIR studies confirmed that BAB could be electro-oxidized into radical cations and then electropolymerized via para (N-N) and/or ortho (N-C) coupling reactions to form polymers with a larger conjugated π-electron system. The surface morphology of the poly-BAB was also investigated with atomic force microscopy (AFM) and scanning electron microscopy (SEM).     

Electrochemical oxidation mechanisms of different type 1,4-dihydropyridine derivatives in acetonitrile

A series of 32 substituted dihydropyridines of essentially two types (PyH and PyR) was electrochemically oxidized at a platinum electrode in acetonitrile. Based upon voltammetric experiments in anhydrous, acid, basic and neutral, partially aqueous media, on cp. coulometric results and on preparative electrolyses, side reactions were detected within the framework of the investigated electro-oxidation mechanism; these reactions elucidate some as yet non-investigated aspects in the behaviour of these compounds. With the PyH type a one-electron EC mechanism was also discovered in addition to the dominating ECE mechanism; moreover a pronounced protonation of the reactant was observed. With the PyR type compounds relatively stable radical cations homogeneously catalyse the oxidation of acetonitrile giving rise to proton splitting off on account of the oxidation proper. On the basis of the above results, overall mechanisms of the electro-oxidation of both 1,4-dihydropyridine types in acetonitrile were suggested or supplemented.     

Alternate and random (co)polymers composed of anthracene and chloromethylstyrene units through controlled radical ring-opening polymerization: Synthesis,post-functionalization,and optical properties

A cyclic monomer containing the chloromethyl unit 10-methylene-9,10-dihydroanthryl-9-spiro(4′-chloromethylphenyl)cyclopropane (MDCMS) was polymerized using a controlled radical ring-opening polymerization via a reversible addition-fragmentation chain transfer (RAFT) process to afford a nonconjugated alternate polymer composed of anthracene and chloromethylstyrene (CMS) units. Well-defined random copolymers were obtained through the ring-opening RAFT copolymerization. Various functional groups were incorporated into the alternate polymer. The alternate polymer containing imidazole rings exhibited fluorescence quenching as a result of charge transfer. Fluorescence resonance energy transfer (FRET) was observed in the alternate polymers containing naphthalene and thiophene rings. The random copolymers obtained by copolymerization followed by post-functionalizations exhibited characteristic optoelectronic properties that differed from those of the alternate polymers.     

The chemistry of alkyl dihalides in zeolite NaX at room temperature

Alkyl dihalides adsorbed in NaX zeolite undergo room temperature, substitutional dehalogenation, single dehydrohalogenation, combined dehalogenation–dehydrohalogenation, or two consecutive dehydrohalogenations. The preference for a particular reaction depends on the nature and relative positions of the halogens, and on alkyl chain length. Nuclear magnetic resonance chemical shifts and mass spectrometric assignments to the reagents and products indicate the particular reactions taking place.All of the alkyl dihalides containing the iodo group (diiodoalkanes) studied (αα, αβ, α,γ) undergo only substitutional dehalogenation to form zeolite bound iodoalkoxy. The same chemistry was observed with both short and long chain diiodoalkanes. The dichloroalkane and dibromoalkane chemistry is dependent on the relative halogen positions and the alkyl chain length. The α, α dichloroalkanes and dibromoalkanes examined by us undergo single dehydrohalogenation, with the exception of 2,2-dichloropropane, which forms a mixture of dehydrohalogenation and substitutional dehalogenation products. The chemistry of α, β alkyl dihalides (Cl, Br) in NaX is dependent on the carbon chain length. The dihaloethanes (Cl, Br) undergo both substitutional dehalogenation and dehydrohalogenation. As the chain length increases to three carbon atoms or more, only dehydrohalogenation reactions take place. No alkyne products were observed with α, β dichloroalkanes and dibromoalkanes, an indication that NaX is too weak a base to initiate sequential dehydrohalogenations. The chemistry of α, γ dichloroalkanes and dibromoalkanes were also dependent on the chain length. The α, γ dihalopropanes (Cl, Br) in NaX form a propene-framework bound product, associated with dehydrohalogenation and subsequent substitutional dehalogenation. The α, γ dihalobutanes (Cl, Br) undergo two consecutive dehydrohalogenations to form dienes.     

Structure and Reactions of Aliphatic Bridged Bifunctional Radical Ions: Exploring Fine-Tuning in Radiation Chemistry

Bridged bifunctional molecules of general structure X (CH₂)_n Y are useful models for investigations into the effects of intra- and intermolecular interactions in primary radiation-induced processes, with a number of implications for radiation chemistry, radiobiology, and molecular electronics. This short Review presents an outline of recent studies on the structure and reactivity of aliphatic bifunctional radical ions in low-temperature matrices using EPR spectroscopy and quantum-chemical calculations. Both EPR data and DFT calculations for radical cations show that the delocalization of charge and spin density occurs if XY or X and Y have close electronic properties. If the difference in the ionization potentials between X and Y is large, localized radical cations are observed with ground-state properties close to those of the corresponding monofunctional species. Nevertheless, the remote second functional group may affect the photochemistry of such radical cations at a specific bridge length, probably due to intramolecular interactions in a certain conformation. The stabilization of bridged bifunctional radical anions containing two carbonyl groups was found to be very sensitive to the local environment, which may be described in terms of a microsolvation model at the MP2 level of theory. Two independent reactions pathways with excess electrons, yielding different types of localized radical anions, were demonstrated for asymmetrical bifunctional molecules. The obtained results and their implications are discussed in terms of fine-tuning effects in radiation-induced chemical processes in condensed phases.     

The Competition Kinetics of Unbranched Chain Processes of Free-Radical Addition to Double Bonds of Molecules with the Formation of 1:1 Adducts

Abstract

Based on a kinetic model involving competing parallel reactions for free-radical addition to the double bond of a molecule with the formation of 1:1 adduct and participation of three radical types in the chain propagation, versions of the rate equation with 1 - 3 measurable parameters are derived. These versions make it possible to describe the nonmonotonic (with maximum) dependence of the formation rate of an addition product on concentration of the unsaturated compound. The unbranched chain process occurs in binary liquid systems comprising saturated and unsaturated components at comparable concentrations. Application of the competition kinetics of free-radical addition to oxidation of some hydrocarbons is discussed when the reaction that competes with chain propagation reactions involving the alkylperoxy radical RO₂ gives the cyclic alkylhydrotetraoxy radical [R(_?H)O₄H] as a less reactive radical inhibiting the chain process of formation of the main products of oxidation.     

Optical and vibrational studies on single walled carbon nanotubes/short oligo‐para‐methoxy‐toluene composite

In a solution state, an oligophenylene prepared by electrochemical oxidation of para‐methoxy‐toluene exhibited luminescence in the violet‐to‐blue region. However, in a solid state, a clear red shift was observed as a signature of a supramolecular π‐stacking interaction between oligomer chains. In a de‐doped state, by chemical reduction, a fine structure in the form of two peaks was observed and luminescence intensity was strongly improved. When mixed with single walled carbon nanotubes (SWNTs), a quenching in the luminescence intensity accompanied by a slight blue shift of the PL peak of the nanocomposite was observed. This implies the shortening of the oligomer's effective π‐conjugation length caused by the added amount of SWNTs. A charge transfer in the photo‐excited state was also noted. The interaction taking place between the two materials was supported by optical infrared absorption and Raman scattering measurements and then a functionalizing mechanism was proposed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Interactions Between Gold Nanoparticles and Polymer Bearing 3-Styryl Thiophene Chromophores

The interactions between gold nanoparticles and a novel acrylate copolymer bearing 3-styryl thiophene chromophores were studied spectrally and electrochemically. The emission intensity of the polymer solution can be quenched by gold nanoparticles. Collisional quenching is likely the main mechanism for the deactivation process and heterogeneous electron transfer takes place in the process. For the solid polymer film, the presence of gold nanoparticles reduces the emission intensity of the single chromophore as well as the intensity of the excimers. Cyclic voltammetry (CV) investigations indicate that the polymer solution exhibits no oxidation wave. However, in the presence of gold nanoparticles, either by directly addition to the polymer solution or by deposition on the ITO electrode, the polymer solutions possess distinct CV oxidation peak(s), indicating that the gold nanoparticles may mediate the contact and enhance the electron transfer between the electrode and chromophores.     

From short conjugated oligomers to conjugated polymers. Lessons from studies on long conjugated oligomers

Given their utility in a variety of electronic devices, conjugated oligomers and polymers have attracted considerable research interest in recent years. Because polymeric materials consist of very large molecules with a range of molecular weights (that is, they are polydisperse), predicting their electronic properties is a complicated task. Accordingly, their properties are typically estimated by extrapolation of oligomeric properties to infinite chain lengths. In this Account, we discuss the convergence behavior of various electronic properties of conjugated oligomers, often using thiophene oligomers as a representative example. We have observed some general trends in our studies, which we briefly summarize below for five properties. Most of the calculated values are method dependent: the absolute values can be strongly dependent on the computational level used. Band Gap. The generally accepted approximation used to estimate polymer band gap, whereby a plot of HOMO-LUMO gap versus 1/n (where n is the number of monomer units) is extrapolated to infinite n, fails for long oligomers, because convergence behavior is observed for band gaps. At the B3LYP/6-31G(d) level, it is possible to extrapolate oligomer HOMO-LUMO gaps with a second-order polynomial equation. Alternatively, PBC/B3LYP/6-31G(d) is a very good method to reliably predict the band gap of conjugated polymers. Reorganization Energy. Values of the internal reorganization energy (λ) do not scale linearly with 1/n, instead exhibiting an inverse correlation with the square-root of the number of monomer units for n = 2-12. For larger n (10-50), a linear relationship is observed between reorganization energy and the reciprocal chain length, and the extrapolation approaches λ ≈ 0 for infinite numbers of oligomer rings. Ionization Potential. The relationship between the first adiabatic ionization potential IP(1a) of oligothiophenes and oligoselenophenes and chain length linearly correlates with an empirically obtained value of 1/(n(0.75)). The first vertical ionization potential (IP(1v)) linearly correlates with a similarly empirically obtained value of 1/(n(0.70)). Polaron-Bipolaron Balance. The contribution of a polaron pair to the electronic structure of the short oligothiophene dication is small; for medium-length oligothiophene chains, the contribution from the polaron pair state begins to become significant. For longer (above 20-mer) oligothiophenes, the polaron pair state dominates. A similar picture was observed for multications as well as doped oligomers and polymers. The qualitative polaron-bipolaron picture does not change when a dopant is introduced; however, quantitatively, the bipolaron-polaron pair equilibrium shifts toward the bipolaron state. Disproportionation Energy. The stability of a single oligothiophene dication versus two cation radical oligothiophene molecules increases with increasing chain length, and there is an excellent correlation between the relative disproportionation energy and the inverse of chain length. A similar trend is observed in the disproportionation energies of oligothiophene polycations as well as doped oligomer and polymers. We also examine doped oligothiophenes (with explicitly included counterions) and polymers with a repeating polar unit. From our experience, it is clear that different properties converge in different ways, and long oligomers (having about 50 double bonds in the backbone) must often be used to correctly extrapolate polymer properties.     

The influence of various reaction parameters on the performance of (α‐diimine)nickel(II) catalysts in ethylene oligomerization reactions

Modified (α‐diimine)nickel(II) catalysts are suitable for ethylene oligomerization reactions. Due to the mechanism (“chain running”), the formation of double‐bond isomers and branched olefins can be observed. The obtained oligomer mixtures show a Schulz–Flory distribution. Increasing ethylene pressure favors the selectivity of α‐olefin formation. The same effect can be observed when Lewis bases like thiophene or furane are added to the oligomerization reaction mixture. These results can be related to an interaction of the additives with the catalytic active species during the oligomerization process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1356–1361, 2003     

A comparative study of the direct anodic oxidation of olefins and acetylenes in non aqueous solvents

The results of electrode kinetic, preparative and theoretical studies of the direct anodic oxidation of related olefins and acetylenes are compared (phenylacetylene/styrene; vinylacetylene/butadiene; 1,4-diphenylbutadiene/1,4-diphenylbutadiyne).Modified HMO-calculation (β-modification according to bond lengths) predict the observed difference of the half wave potentials of related olefins and acetylenes qualitatively. However the HMO-calculations do not allow the precise prediction of the reactivities of anodically formed radical cations of the acetylenes except for the highly conjugated diphenylbutadiyne. Electrode kinetic and preparative data of the olefin and acetylene oxidation show that both react in the same way ie, are oxidized in the adsorbed state to yield monomeric and dimeric products. The remarkably low dimer yield in the acetylene oxidation is supposed to be due to the decreased adsorbability of the acetylenes at the higher anode potentials which are necessary to oxidize them. This phenomenon is observed, too, if olefins with different half wave potentials are compared.     

Kinetics and Mechanism of Liquid-Phase Oxidation of Thiophene over TS-1 Using H2O2 Under Mild Conditions

Thiophene is a typical thiophenic sulfur compound in gasoline. Using n-octane containing thiophene as the model compound, the oxidation of thiophene, which is a key step for the oxidative deep desulfurization of gasoline, was carried out to study the reactivity of thiophene in oxidation reactions. It has been observed that thiophene oxidation can occur using water or t-butanol as solvent. Kinetics of the reaction shows a pseudo-first-order toward thiophene or catalyst and a zero order toward hydrogen peroxide. The mechanism for this unique reaction was proposed as the activation of conjugated electron in thiophene ring.     

Recent advances in electrochemistry of diamond

Conductive boron-doped chemically vapour-deposited diamond thin film and honeycomb electrodes were examined for various possible applications in electroanalysis and electric double layer capacitor applications, respectively. The possibility of voltammetric study of electrochemical reactions occurring at high oxidation and high reduction potentials was demonstrated at diamond electrodes, taking histamine and carbon tetrachloride as respective examples. High sensitivity and high stability of this electrode were demonstrated for the determination of histamine and sulfadiazine by flow injection analysis method. Nanostructured honeycomb diamond electrodes, prepared by oxygen plasma etching, exhibited a wide potential window similar to that of as-grown film but a capacitance 200 times higher than that of the as-grown film. These results indicate the usefulness of diamond electrode for electroanalysis and double layer capacitor applications.