Copolymers of ε-caprolactam and polypropylene oxide via anionic polymerization: synthesis and properties

Copolymers with an elastic polypropylene oxide (PPO), middle block in the main chain of poly(ε-caprolactam) were synthesized via activated anionic ring opening polymerization of ε-caprolactam (CL) in the presence of a basic initiator sodium salt of CL (Na-CL) and effective bifunctional polymeric activators (PACs). By varyng the molecular weight, two types of PACs were synthesized based on carbamoyl derivatives of hydroxyl terminated PPO with isophorone diisocyanate and were blocked with CL. The formation of copolymers has been confirmed by proton nuclear magnetic resonance spectroscopy (¹H–NMR) and Fourier transform infrared spectroscopy (FT-IR). The influence of the molecular weight of the PACs, the CL/PAC ratio and polymerization conditions on the conversion, intrinsic viscosity and polymerization kinetics, was investigated. The calorimetric, wide-angle X-ray diffraction (WAXD), thermogravimetric analysis (TGA), notched impact test and dynamic mechanical thermal analysis (DMTA) were performed to estimate the influence of the composition ratio and the type of PACs on the physical, thermal, and mechanical properties of the copolymers. The use of the synthesized PACs reduced the polymerization time to several minutes. The copolymers showed improved impact resistance up to more than two times higher than those of the polyamide 6 (PA-6) homopolymer, without significant changes in their high melting temperatures.     

Preparation of poly(methyl methacrylate) macromonomer by radical polymerization in the presence of methyl α-(bromomethyl)acrylate and copolymerization of the resultant macromonomer

Radical polymerization of methyl methacrylate (MMA) in the presence of methyl -(bromomethyl) acrylate yielded poly-(MMA) bearing the 2-methoxycarbonylallyl end group through chain reaction involving bimol ecular termination. The molecular weight of the resultant polymer was effectively controlled with a small amount of the bromomethylacrylate added; the chain transfer constant was estimated to be 0.9. The poly (MMA) with the unsaturated end group (

Graft copolymers of poly(methyl methacrylate) and polyamide-6 via in situ anionic polymerization of ε-caprolactam and their properties

Graft copolymers of poly(methyl methacrylate) and polyamide-6 (PMMA-g–PA6) were investigated via in situ anionic polymerization of ε-caprolactam, using PMMA precursors with N-carbamated caprolactam pendants (PMMA–CCL) as macroactivators and sodium caprolactamate as catalyst. Three grades of PMMA–CCLs obtained by free radical copolymerization were used for synthesizing the PMMA-g–PA6 copolymers with different PMMA content. The resulting graft copolymer was characterized by Fourier-transform infrared spectroscopy and selective extraction. Scanning electron microscopy is used to clarify the phase morphology of obtained polymer by fracture surface. The thermal property, crystallinity and dimensional stability of graft copolymer were studied using differential scanning calorimetry, X-ray diffraction and water absorption measurement. The results show the T_g of graft copolymer is higher than that of neat PA6, but the onset and peak points of graft copolymer melting point are shifted to lower temperature. The percentage crystallinity and water absorption of PMMA-g–PA6 copolymer decrease with increasing PMMA content, but the crystal structure of PA6 is scarcely affected by the presence of PMMA. Graft copolymers have improved dimensional stabilities relative to neat PA6. Upon the incorporation of 19.9 wt% PMMA into PA6, the water absorption of PMMA-g–PA6 copolymer has been reduced from 4.8 for neat PA6 to 2.1%.     

Electrochemical deposition of zinc–polystyrene composites in the presence of surfactants

The electrochemical codeposition of polystyrene particles and zinc on a rotating cylinder electrode was investigated. Rheological measurements indicate strong aggregation of the PS particles in the zinc deposition electrolyte. Addition of cetylpyridinium chloride, a cationic surfactant, prevents aggregation and enhances polystyrene codeposition. Other surfactants also increase suspension stability, but diminish polystyrene codeposition, irrespective of their charge. Hence, the surfactant charge does not affect polystyrene codeposition. The variation of polystyrene incorporation with the amount of suspended polystyrene, current density and electrode rotation speed signifies that polystyrene codeposition with zinc is determined by the competition between particle removal forces and particle adhesion forces at the cathode surface. The effect of the surfactants can be related to changes in surface roughness of zinc due to surfactant adsorbed on the electrode. Cetylpyridinium chloride behaves differently from the other surfactants, because it is reduced at the cathode.     

Angular–linear isomerization on the hydrogenation of phenanthrene in the presence of iron-containing catalysts

A method for the preparation of iron and iron–cobalt oxide catalysts on a carbon support is described. The formation of angular–linear isomerization products in the high-temperature hydrogenation of phenanthrene in the presence of the synthesized catalysts was found.     

Research on the Degradation Kinetics Model in the Drying Process of Chinese Herb

Curative compositions such as catolpol in Rehmannia Glutinosa, flavone in Ophiopogon Japonicus and ginsenoside Re in Panax Ginseng in Chinese herbs were measured as the experimental indices by the method of high performance liquid chromatography under different drying conditions. The reaction order and parameters of the degradation kinetics model were determined and the model was verified by experiments. It was indicated that by comparing with the thin drying method, the prospective model could predict the degradation of curative compositions with drying time, temperature and moisture content of herbal materials with enough precision and could be used to simulate the degradation in the drying process of Chinese herb.     

Coupling effect of fullerene chloride in anionic polymerization

以氯化富勒烯(C60 Cln)为偶联剂,用n-BuLi引发苯乙烯负离子聚合.紫外光谱分析表明,产物中含有C60.GPC检测显示,试样的相对分子质量分布比母体聚合物要宽,在高相对分子质量部分出现了含C60的新峰,证明发生了偶联反应.平均每个C60上接有2条聚苯乙烯链.     

ϵ-OA for the solution of bi-objective generalized disjunctive programming problems in the synthesis of nonlinear process networks

There has been an increasing interest in multicriteria optimization (MCO) of nonlinear process network problems in recent years. Several mathematical models have been developed and solved using MCO methodologies including ϵ-constraint, weighted sum, and minimum distance. In this paper, we investigate the bi-objective nonlinear network synthesis problem and propose an effective algorithm, ϵ-OA, based on augmented ϵ-constraint and logic-based outer approximation (OA). We provide theoretical characterization of the proposed algorithm and show that the solutions generated are efficient. We illustrate the effectiveness of our novel algorithm on two benchmark problems. The ϵ-OA is compared to the straightforward use of OA with augmented ϵ-constraint algorithm (ϵ-con + OA), the augmented ϵ-constraint without OA (ϵ-MINLP), and the traditional ϵ-constraint (T-ϵ-con). Based on the results, our novel algorithm is very effective in solving the bi-objective generalized disjunctive programming problems in the synthesis of process networks.     

Isomerization of α-pinene oxide in the presence of methyltrioxorhenium(VII)

The catalytic performance of methyltrioxorhenium(VII) (MTO) has been investigated for the first time in the isomerization of α-pinene oxide (PinOx) into campholenic aldehyde (CPA). The high isomerization activity of MTO is coupled with high selectivity to CPA: CPA yield of up to 87% (100% conversion) was obtained by using α,α,α-trifluorotoluene as solvent at 15 °C. Catalyst recycling is possible in a relatively simple fashion by using MTO coupled to an appropriate ionic liquid. The catalytic application of MTO in the isomerization of PinOx versus the integrated epoxidation–isomerization process of the conversion of α-pinene into CPA is discussed.     

Stereochemistry of the hydroperoxides formed during autoxidation of CLA methyl ester in the presence of α-tocopherol

The initial steps in the autoxidation of CLA methyl ester are poorly understood. The aim of this study was to determine the stereochemistry of the hydroperoxides formed during autoxidation of CLA methyl ester in the presence of a good hydrogen atom donor. For this purpose, 9-cis, 11-trans CLA methyl ester was autoxidized in the presence of α-tocopherol under atmospheric oxygen at 40°C in the dark. The CLA methyl ester hydroperoxides were isolated, reduced to the corresponding hydroxy derivatives, and separated by HPLC. The stereochemistry of seven hydroxy-CLA methyl esters was investigated. The position of the hydroxy group was determined by GC-MS. The geometry as well as the position of the double bonds in the alkyl chain was determined by NMR. In addition, the ¹³C NMR spectra of six hydroxy-CLA methyl esters were assigned using COSY, gradient heteronuclear multiple bond correlation, gradient heteronuclear single quantum correlation, and total correlation spectroscopy experiments. The autoxidation of 9-cis, 11-trans CLA methyl ester in the presence of a good hydrogen atom donor is stereoselective in favor of one geometric isomer, namely the 13-(R,S)-hydroperoxy-9-cis, 11-trans-octadecadienoic acid methyl ester. Three types of conjugated diene hydroperoxides are formed as primary hydroperoxides: trans,trans hydroperoxides (12-OOH-8t,10t and 9-OOH-10t,12t), a cis,trans hydroperoxide with the trans double bond adjacent to the hydroperoxide-bearing carbon atom (13-OOH-9c,11t), and a new type of cis,trans lipid hydroperoxide with the cis double bond adjacent to the hydroperoxide-bearing carbon atom (8-OOH-9c,11t). In addition, three nonkinetic hydroperoxides (13-OOH-9t,11t, 8-OOH-9t,11t, and 9-OOH-10t,12c) are formed. This study supports the theory that CLA methyl ester autoxidizes at least partly through an autocatalytic free radical reaction. The complexity of the hydroperoxide mixture is due to formation of two different pentadienyl radicals. Moreover, the stereoslectivity in favor of one geometric isomer can be explained by the selectivity of the two previous steps: the preferential formation of a W-conformer of the pentadienyl radical over the Z-conformer, and regioselectivity of the oxygen addition to the pentadienyl radical.     

Analysis of the electrochemical reactivity of natural hemozoin and β-hemozoin in the presence of antimalarial drugs

We report an evaluation of the reactivity of hemozoin (HZ) and β-hemozoin (β-HZ) obtained from the Triatoma Meccus longipennis, alone and in combination with quinine and amodiaquine. Using cyclic voltammetry and carbon paste electrodes, the redox processes that these compounds undergo were analysed. The results indicated that the atom Fe presence, the substance concentration, the drugs existence and the nature of the electrolytic medium are important in the redox processes. The strongest reactivity was for β-HZ from Triatoma, which suggests that cellular molecules are embedded in an oxidising environment due to the presence of β-HZ and indicates that like HZ, β-HZ could be associate with phospholipid bilayers and interfere with their physical and chemical integrity, contributing to membrane breakdown and hyper-oxidation of molecules. It was further observed that when measuring the reactivity of HZ and β-HZ with quinine and amodiaquine, a more oxidative stress was generated between the second one and the β-HZ, which could explain the effectiveness of amodiaquine as a better antimalarial drug. Finally, it was concluded that electrochemical evaluation may be a convenient tool in determining the efficiency of antimalarial drugs and the identification of their redox processes.     

Hydroformylation of olefins with water-soluble rhodium catalysts in the presence ofα-cyclodextrin

Hydroformylation of hex-1-ene using a water soluble rhodium catalyst HRh(CO)[PPh₂(m-C₆H₄SO₃Na)]₃ (HRh(CO)(TPPMS)₃) (I), gives lower yields when-cyclodextrin is added to the biphasic reaction system implying an interaction between the cyclodextrin and rhodium catalyst.     

Kinetics and latex particles analysis on styrene emulsion polymerization induced by <Superscript>60</Superscript>Co γ rays in presence of anionic polymerizable emulsifier

⁶⁰Co γ rays induced styrene emulsion polymerizations were carried out with sodium undec-10-enoate (UDNa) as emulsifier at room temperature and the different kinetics was discussed. The influence of absorbed dose rate, monomer concentration and emulsifier concentration on kinetics and latex particles was studied. The polymerization kinetics relation was found as R _P ∝ D ^0.37 · M ^0.75 · E ^0.70 (R _P , maximum polymerization rate; D, absorbed dose rate; M, monomer concentration; E, emulsifier concentration). The particles’ diameter increases and particle size distribution (PSD) becomes narrower with the decrease of absorbed dose rate and increase of monomer content. The effect of UDNa content on particles’ diameter and particle size distribution is the same as that of emulsifier in conventional emulsion system. This type of emulsion polymerization can easily form monodisperse particles.     

Copolymerization in dispersion of divinyl benzene–maleic anhydride in the presence of silylated montmorillonite clays

Sodium montmorillonite (NaMMT clay) derivatives were encapsulated in polymer particles obtained through dispersion copolymerization of divinyl benzene (DVB) with maleic anhydride (MA). To evidence the effect of alkyl monoalkoxysilanes upon MMT reaction, a variety of MMT clay functional derivatives were investigated. Particles with an increased size of modified MMT clay dispersed in dichloromethane were obtained using alkyl monoalkoxysilanes with a longer hydrocarbon chain. Relatively long hydrocarbon chains can exhibit a low substitution degree of MMT clay with alkyl monoalkoxysilanes. MMT class with a low substitution degree leads in the presence of alkoxysilanes to particles with average size between 700 and 1200 nm, and when DVB–MA copolymer is added the particles size decreases (~480 nm). The influence of layered silicates on the thermal stability of DVB–MA copolymer as a function of the used vinyl siloxanes derivatives for functionalization of MMT, on one hand, and the nonlinear variation of refractive index of used silanes on the other hand, pointing out the autoassociation during initial reaction of substitution.     

Synthesis of block copolymers of ε-caprolactone and lactide in the presence of lithium t-butoxide

Summary High molecular mass copolymers with microphase separation can be obtained in block copolymerization of -caprolactone with L,L- and D,L-lactide carried out in the presence of lithium t-butoxide. A kind of solvent applied strongly affects the molecular mass and polydispersity index of obtained copolymers.The study has been supported by the research program (Project 4-1743) of the Committee of Scientific Research in Poland.     

Kinetics and mechanism of ethylene homopolymerization and copolymerization reactions with heterogeneous Ti-based Ziegler–Natta catalysts

A detailed kinetic analysis of ethylene homopolymerization reactions and its copolymerization reactions with 1-hexene with a supported Ti-based Ziegler–Natta catalyst (reactions in the absence and the presence of hydrogen) shows a number of distinct kinetic features which are interpreted as a manifestation of multi-site catalysis; the catalyst contains several types of polymerization centers which differ in stability and formation rates, the molecular weight of polymers they produce, and in their response to the presence of α-olefins and hydrogen. All these effects require introduction of a special kinetic mechanism which postulates an unusually low activity of growing polymer chains containing one ethylene unit, the Ti–C₂H₅ group, in the ethylene insertion reaction into the Ti–C bond. This peculiarity of the Ti–C₂H₅ group, which is probably caused by its β-agostic stabilization, predicts two kinetic/chemical features of ethylene polymerization reactions which have not been described yet, the deuterium effect on the homopolymer structure and the activation effect of α-olefins on chain initiation. Both effects were confirmed experimentally. This revised version was published online in June 2006 with corrections to the Cover Date.     

Autoignition mechanism of dimethyl ether–air mixtures in the presence of atomic iron

The search for reactive additives capable of reducing the combustibility of dimethyl ether is an important problem due to the widening use of ether as an alternative environmentally friendly motor fuel. This paper presents a numerical study of the autoignition chemistry of mixtures of dimethyl ether with air in the presence of atomic iron. Atomic iron, which is an effective inhibitor of premixed laminar hydrocarbon flames, was found to shorten the induction period. However, the additive affects only the first stage of the induction period. The mechanism of promotion of the low-temperature oxidation of dimethyl ether–air mixtures by atomic iron is the formation of hydroxyls in reactions involving iron compounds. Since the additive hardly changes the duration of the second stage of the induction period, it can be suggested that OH radicals play an insignificant role in the low-temperature oxidation of dimethyl ether at this stage.     

Physico-chemical properties of lignin–alginate based films in the presence of different plasticizers

A lignin–alginate blended film was prepared in the presence of three different plasticizers, viz. glycerol, epichlorohydrin (EPC) and poly(ethylene glycol) (PEG) and the effect of each plasticizer was studied on physico-chemical properties of the blended film. Lignin extracted from Acacia wood by alkali extraction process was blended with alginate to obtain lignin–alginate film in the presence of different plasticizers. A film plasticized with glycerol displayed higher solubility and swelling percentage as compared to EPC and PEG plasticized films. The highest tensile strength was observed for film plasticized with PEG, and none of the plasticizers made any significant change on the bursting strength of the film. Incorporation of lignin considerably improved the light barrier properties of the films. Fourier transform infrared spectroscopy study of films suggested the existence of hydrogen bonding between lignin–alginate in the presence of plasticizers. In addition, EPC plasticized film displayed highest thermal stability, as confirmed by thermogravimetric analysis. Further studies demonstrated that plasticizers significantly affected the physico-chemical properties of the blended films. In conclusion, lignin–alginate film plasticized with EPC presented better physico-mechanical and light barrier properties which could be used in packaging and coating applications.