Melting behaviour of gelspun/drawn polyolefins

The melting behaviour of gelspun/drawn UHMW-PE and UHMW-PP fibres was investigated. Unconstrained UHMW-PE and UHMW-PP fibres melt at 142°C and 170°C, respectively. Upon constraining, by holding the fibres at a fixed length or by embedding the fibres in a matrix, an increase in the melting temperature of both fibres is observed. In the case of UHMW-PE fibres a solid-solid phase transition in polyethylene at 155°C from the orthorombic to the hexagonal crystal structure occurs. Above 155°C, the fibres can not sustain any load. This solid-solid phase transition at 155°C sets an upper limit to both the maximum curing and continuous use temperature of PE-fibre reinforced composites. In gelspun/drawn UHMW-PP, such a detrimental solid-solid phase transition is absent, and therefore the increase in melting temperature can be utilized effectively. For example, heating of UHMW-PP fibres for 30 minutes at 200°C does hardly affect the room temperature Young's modulus and tensile strength if the fibre is constrained during heating.     

Mechanism of the modification of polyolefins by organosilicon liquids

Conclusions Thermochemical modification of polyolefins with organosilicon liquids of linear structure leads to the formation of the copolymers of the following structure: Si-O-R and Si-0-CH₂-R, where R is the polyolefin radical.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 797–801, April, 1970.     

Melting point depression of ionic liquids confined in nanospaces

A new physical method was proposed to control the liquid properties of room temperature ionic liquids (RT-ILs) in combination with nanoporous materials; the melting point of ILs confined in nanopores remarkably decreases in proportion to the inverse of the pore size.     

Heterogeneous dehalogenation of arylhalides in the presence of ionic liquids

Dehydrohalogenation of haloaromatics in ionic liquids derived from ethylmethylimidazolium or similar salts has been performed using Pd? C, Pd(OAc)₂ and other catalysts using formate salts as a hydrogen source. In the ionic liquid [emim][BF₄], chlorobenzene was dehalogenated by up to 40%, bromobenzene up to 25% and iodobenzene up to 41% in 2 h. Reactions in the absence of the ionic liquid were also performed. Copyright © 2007 John Wiley & Sons, Ltd.     

Biased spectroscopic protein quantification in the presence of ionic liquids

Owing to their unique physicochemical properties, ionic liquids have gained much recognition as solvents or co-solvents in a wide variety of biochemical applications. In the context of protein analytics, four similar 1-alkyl-3-methylimidazolium-based ionic liquids have been analysed for their applicability as co-solvents. Spectroscopic bovine serum albumin (BSA) quantification experiments in the presence of ionic liquids were performed and for two ionic liquids a concentration-dependent effect has been found that can lead to biased protein quantification. It could be shown that the biased spectroscopic analysis of the tested ionic liquids is dependent on the length of the alkyl side chain (>C₄) of the 1-alkyl-3-methylimidazolium-based cation, and the chaotropicity of the anion. Once accounted for and properly calibrated when using spectroscopic methods, these effects can be avoided thus facilitating correct protein quantification in the presence of ionic liquids.     

Manifestations of probe presence on probe dynamics in supercooled liquids

Experimental studies that follow behavior of single probes embedded in heterogeneous systems are increasingly common. The presence of probes may perturb the system, and such perturbations may or may not affect interpretation of host behavior from the probe observables typically measured. In this study, the manifestations of potential probe-induced changes to host dynamics in supercooled liquids are investigated via molecular dynamics simulations. It is found that probe dynamics do not necessarily mirror host dynamics as they exist either in the probe-free or probe-bearing systems. In particular, for a binary supercooled liquid, we find that smooth probes larger than the host particles induce increased translational diffusion in the host system; however, the diffusion is anisotropic and enhances caging of the probe, suppressing probe translational diffusion. This in turn may lead experiments that follow probe diffusion to suggest Stokes-Einstein behavior of the system even while both the probe-free and probe-bearing systems exhibit deviations from that behavior.     

Palladium-catalyzed hydroesterification of styrene derivatives in the presence of ionic liquids

The palladium-catalyzed hydroesterification of olefins occurs efficiently in a range of ionic liquid media. Selectivities ranging from 5-7:1 for the linear ester were obtained with styrene in a range of IL solvents. The use of ILs allowed the catalyst to be easily separated from the organic product by either extraction or distillation. The (Ph₃P)₂PdCl₂ precatalyst could be recovered unchanged from the ionic liquid phase. The IL/catalyst phase could be recycled five times with an average yield of 68%.     

Reverse ATRP process of acrylonitrile in the presence of ionic liquids

An ionic liquid, 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([C₄mim] [BF₄]), was first used as the solvent in azobisisobutyronitrile (AIBN)‐initiated reverse atom transfer radical polymerization (RATRP) of acrylonitrile with FeCl₃/succinic acid (SA) as the catalyst system. The polymerization in [C₄mim][BF₄] proceeded in a well‐controlled manner as evidenced by kinetic studies. Compared with the polymerization in bulk, the polymerization in [C₄mim][BF₄] not only showed the best control of molecular weight and its distribution but also provided rather rapid reaction rate with the ratio of [C₄mim][BF₄] at 200:1:2:4. The polymerization apparent activation energies in [C₄mim][BF₄] and bulk were calculated to be 48.2 and 55.7 kJ mol^?1, respectively. Polyacrylonitrile obtained was successfully used as a macroinitiator to proceed the chain extension polymerization in [C₄mim][BF₄] via a conventional ATRP process. [C₄mim][BF₄] and the catalyst system could be easily recycled and reused after simple purification and had no effect on the living nature of polymerization. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2701–2707, 2008     

Preparation of 3,6-dibenzoylacenapthene in the presence of Lewis acidic ionic liquids

The reactivity of Lewis acidic ionic liquids for the acylation of acenaphthene to 3,6-dibenzoylacenaphthene was investigated. Ionic liquids of different alkyl chain length and metal chloride were synthesized and tested for the reaction to discuss the effects of Lewis acidity of the ionic liquid on the alkylation. Pure 3,6-dibenzoylacenaphthene was obtained and the structure of 3,6-dibenzoylacenaphthene was identified by GC/MS, FT-IR and ¹H NMR spectra. [Emim]C1/A1C1₃ ionic liquid was found to be the most active catalyst in the acylation. The yield of 3,6-dibenzoylacenaphthene was up to 89.6% and the selectivity towards 3,6-dibenzoylacenaphthene was up to 92.2%. The experiment shows that [Emim]Cl/AlCl₃ can be used as both catalyst and solvent, it is reusable and environmentally friendly for the preparation of 3,6-dibenzoylacenaphthene.     

Stereoselective oxidation of methyl phenyl sulfide in the presence of chiral ionic liquids

Several ionic liquids containing a chiral center either in the cation or in the anion have been prepared. They have been applied as catalysts and solvents for stereoselective oxidation of methyl phenyl sulfide to obtain the respective sulfoxide.     

Epitaxy of helical polyolefins

The structural rules which govern the epitaxial crystallisation of polymers - and especially polyolefins - on organic substrates are established. Illustrative examples involve isotactic and syndiotactic polypropylenes and poly( l-butene). Investigation of the film structure by electron microscopy, electron diffraction and atomic force microscopy reveals some unprecedented features, including in particular the selection of the contact plane according to the chirality of its constituent helices, and direct observation of both right and left hands of polyolefin helices.     

Plasma fluorination of polyolefins

ESCA and contact angle measurements were used to characterize the surfaces of Polyethylene and polypropylene films exposed to SF₆, CF₄, and C₂F₆ plasmas. None of these gases polymerized in the plasma. However, all plasma treatments grafted fluorinated functionalities directly to the polymer surfaces. SF₆ plasmas graft fluorine atoms to a polyolefin surface. CF₄ plasmas also react by a mechanism dominated by fluorine atoms, but with some contribution from CF_x-radical reactions. Although C₂F₆ does not polymerize, the mechanism of grafting is still dominated by the reactions of CF_x radicals. For all gases studied, the lack of polymerization is attributed to competitive ablation and polymerization reactions occurring under conditions of ion bombardment.     

Melting behaviour of poly(ethylene oxide) in the presence of solid particles

Colloid and Polymer Science - The melting of poly(ethylene oxide) in the presence of dispersed, solid particles has been observed by differential scanning calorimetry. At low polymer contents,...     

Melting points and other properties of ionic liquids,with emphasis on the pressure dependence

The focus of this letter is on melting points (T _m) of ‘green’ ionic liquids, which have values of T _m around room temperature. To aid in their chemical interpretation, we place some emphasis on T _m as a function of pressure p, in cases where such experimental information is available. Finally, some comments are made on the effects of pressure via isothermal compressibility κ _T and the velocity v _s of sound. Some measurements of κ _T and v _s as a function of p are invoked.     

Post-polymerization functionalization of polyolefins

Polyolefins are macromolecular alkanes and include the most familiar and most commercially produced plastic, polyethylene. The low cost of these materials combined with their diverse and desirable property profiles drive such large-scale production. One property that renders polyolefins so attractive is their resistance to harsh chemical environments. However, this attribute becomes a severe limitation when attempting to chemically convert these plastics into value-added materials. Functionalization of polymers is a useful methodology for the generation of new materials with wide ranging applications, and this tutorial review describes both new and established methods for the post-polymerization modification of polyolefins.