bluuebunny/crossref_metadata_2025_split huggingface dataset:
Developments in the theory of cationic polymerisation. Part IX some effects of the complex formation between cations and monomers
Authors: Plesch P. H. 
Published: March 2011

AbstractThe formation of complexes P+nM between a propagating carbenium ion P+n and the monomer, M, is considered from several points of view ‐ (i) Under the most usual conditions the formation of the P+nM reduces the population of ion‐pairs, P+nA−, drastically. This can account for the frequently found nil‐effect of common ion salts on the rate of attack of carbenium ions on alkenes in initiation, model reactions, and polymerisations. ‐ (ii) The formation of P+nM increases the degree of dissociation α of P+nA−, so that all the estimates of α on which kinetic schemes have been based, are too low. ‐ (iii) The very high polymerisation rates found for n‐donor monomers, say 4‐MeO‐styrene or N‐vinylcarbazole compared to styrene, may be attributable not, primarily, to a difference in rate‐constants, but to a difference in ionic population. This is because the fast P+nM is in greater excess over the slow P+nA− for more strongly complexing n‐donors than for the π‐donors. ‐ (iv) Since the nature of the P+nM is different for every monomer, a comparison of their propagation rate‐constants k+pM is hardly meaningful and valid comparisons can only be made between the k+p of the P+n. The measurement of these requires extreme conditions, either extrapolations to [P+n] = 0 and [M] = 0, or the use of highly polar solvents in which neither M nor the anion can compete with the solvent for the solvation of the P+n.
Functional polymers based on high hydrophilicity of poly(2‐methyl‐2‐oxazoline)
Authors: Saegusa Takeo , Chujo Yoshiki 
Published: March 2011

AbstractPolymers of the family of 2‐substituted 2‐oxazolines have the general structure of poly(N‐acylethylenimine), whose hydrophilic/lipophilic properties vary according to the substituent, i.e., the acyl group of the polymer. Of special interest is the polymer of 2‐methyl‐substituted monomer, which has a strong affinity for water. Another useful feature of the 2‐oxazoline family is the fact that its polymerization reaction is quite clean without disturbance by chain transfer and termination. On the basis of the above characteristics, three kinds of novel materials of functional polymers have been explored:
Non‐ionic polymeric surfactants.
Non‐ionic hydrogels.
Block copolymer with silica gel: Organic/inorganic polymers hybrids.
Copolymer sequence control by ring‐opening polymerization of prestructured cyclic monomers
Authors: Cho Iwhan 
Published: March 2011

AbstractIn search for the new synthetic methods which may lead to the copolymers of controlled mer sequences, several new carbocyclic and heterocyclic monomer systems such as 1,1‐disubstituted 2‐vinylcyclopropanes, 1‐(p‐anisyl)‐2‐vinylcyclopropanes, substituted 3,4‐dihydro‐2H‐pyrans, substituted 4‐vinyl‐2‐oxetanones and α‐vinyl cyclic sulfones were synthesized and their polymerization behaviors were investigated. And other promising monomer systems were also examined.
Synthesis of chitin derivatives and their metal complexes
Authors: Choi Kyu Suk 
Published: March 2011

AbstractThiosemicarbazide, phosphoric acid and amidoxime derivatives of chitosan were synthesized and their ability for metal ion adsorptions was discussed. Thiosemicarbazide derivative, synthesized by treating chlorodeoxychitosan with ammonium thiocyanate followed by treatment with hydrazine, was considered to have cross‐linked network structure. Phosphoric acid derivative containing both N‐phosphonic acid and phosphoric acid groups was synthesized by cyanoethylation of chitosan using acrylonitrile, followed by treatment with hydroxylamine. These derivatives were found to adsorb effectively infinitesimal concentration (ppb order) of uranyl ion in seawater. Stability constants of some metal ion chitosan chelates were determined. To improve the selectivity in the adsorption of metal ions, a novel method utilizing metal ion as a template was adopted, and the results are discussed.
Sequentially ordered, thermotropic aromatic copolyesters: Synthesis and comparison of their properties with random copolyesters
Authors: Jin Jung‐Il , Chang Jin‐Hae , Jo Byung‐Wook , Sung Ki‐Youn , Kang Chung‐Seock 
Published: March 2011

AbstractSynthetic methods of aromatic copolyesters having ordered comonomer sequence are described. In order to obtain a regular sequence copolyester, one first has to prepare a dimeric or trimeric compound with a predesigned sequence via a multistep route and then polycondense it with another difunctional compound. Low reaction temperature is required to avoid the occurrence of undesired interchange reactions that would lead to randomization of the comonomer sequence. Sequentially ordered copolyesters exhibit significant differences in thermal transitions, crystalline properties, and occasionally even in liquid crystallinity when compared with the properties of the corresponding random copolyesters. According to the preliminary results randomization in comonomer sequence of sequentially regular aromatic copolyesters above their melting points is rather rapid.
Synthesis of novel conducting polymers by cyclopolymerization of dipropargyl derivatives
Authors: Choi Sam‐Kwon 
Published: March 2011

AbstractCyclopolymerization of dipropargyl derivatives which leads to new conjugated polymers was examined by various transition‐metal catalyst systems. The highly colored polymers with average molecular weights of 10000–47000 were soluble in common organic solvents. Poly(dipropargyl derivatives) which possess polyene structures having cyclic recurring units in the polymer backbone, have been investigated for their physical properties such as solubility, the nature of doping process, electrical conductivity, and oxidation stability.
Polymer membranes with selective gas and vapor permeation properties
Authors: Strathmann H. , Bauer B. , Kerres J. 
Published: March 2011

AbstractSince many years synthetic membranes have been used in reverse osmosis or ultrafiltration for the separation of aqueous mixtures. More recently the separation of gases and vapors by selective membrane permeation has gained significant technical and commercial interest. The recovery of hydrogen from petrochemical purge gases and ammonia production processes or the removal of CO2 from natural gas by selective membrane permeation are today state of the art procedures. The recovery of organic solvents from waste air streams is another very promising application of synthetic membranes. In this paper the main parameters determining the performance of a membrane in gas and vapor separation are described. The requested intrinsic properties of the polymer to be useful as a barrier for a selective gas and vapor transport are discussed. The preparation of appropriate membranes is described. Their performance in practicle applications is illustrated in selected examples.
Polyurethane IPN membranes
Authors: Kim G. S. , Lee J. H. , Lee Y. K. , Kim S. C. 
Published: March 2011

AbstractHydrophilic PU and hydrophobic PS IPN membranes were prepared and the effect of the synthesis pressure on the pervaporation characteristics of ethanol water mixture was evaluated. Cationic/anionic IPN membranes were prepared from the cationic PU and the anionic acrylic copolymer, and the effects of the composition and the ionic concentration on the permeation characteristics were analyzed. The gas (oxygen and nitrogen) transport of the IPN membranes of PU/PS were also examined. The effect of synthesis temperature and composition of the IPN membranes were analyzed.
Photosensitization of poly(vinyl alcohol)/cerium complexes to produce ion‐exchange resins by graft copolymerization
Authors: Hill David J.T. , Mcmillan Alison M. , O'Donnell James H. , Pomery Peter J. 
Published: March 2011

AbstractAcrylamide can be graft copolymerized onto poly(vinyl alcohol) in aqueous solution with initiation by cerium(IV) under acid conditions in order to produce an appropriately functionalized polymer directly or by subsequent chemical modification. Initiation proceeds through the decomposition of a complex between the PVA1 and Ce(IV) and under normal conditions occurs only through the 1, 2‐glycol units in the PVA1. Illumination by light in the absorption wavelength range of the complex accelerates the rate of graft copolymerization. Moreover, initiation now proceeds through the 1,3‐glycol units.
Recent development in photosensitive resin in Korea
Authors: Hong Sung Il 
Published: March 2011

AbstractThe aim of the review is to introduce some recent progress in the photosensitive polymers in Korea. It is focused to review the research works performed recently in this country, especially in the academic world. As photosensitive polymers, cinnamates of various polymers, azides and diazido compounds, oximeesters or oxime containing polymers, and some other sensitizing polymers were treated, and also sensitizing effects were evaluated.
Biodegradable polymeric matrix for long‐acting and zero‐order release drug delivery systems
Authors: Li You‐Xin , Feng Xin‐De 
Published: March 2011

AbstractThree types of biodegradable triblock copolymers, ABA, ABC and ACB, where A is polycaprolactone (PCL), B is polylactide (PLA) and C is polyglycolide (PGA), were used as matrix to test their controlled release behavior of Levo‐Norgestrel in the form of microsphere. It was verified that the overall release kinetics changes from in vitro first order to zero order when the percentage of PCL segments in all of the block copolymers decreases from 85 % to 60 −65 % with a long‐acting release time of 5 months or more. It is ascribed to the two release mechanisms, the diffusion release, contributed by the PCL segment, and the erosion‐caused release by PLA or PGA segment. At a certain ratio of segments the two release ways make a compromise to a constant rate of release, i. e. a zero‐order kinetics in these multiphase block copolymers.
Stimuli sensitive polymers for drug delivery systems
Authors: Kwon I. C. , Bae Y. H. , Okano T. , Kim S. W. , Berner B. 
Published: March 2011

AbstractTemperature sensitive and electric field sensitive hydrogels were prepared for use in modulated drug release systems. Crosslinked poly(N‐isopropyl‐acrylamide) and its networks, modified with hydrophobic components by copolymerization or by interpenetrating polymer networks (IPNs) formation, were utilized as temperature sensitive hydrogels. Indomethacin (a model solute)‐release from polymer matrix and permeation through polymer membrane demonstrated “on‐off” regulation with temperature fluctuation. This was the result of polymer surface properties rather than bulk swelling, as temperature was changed past the swelling transition temperature range of the polymer. The on‐off regulation in an electric field was also obtained with a positively charged solute (Edrophonium chloride) release in distilled‐deionized water from a matrix of crosslinked poly(2‐acrylamido‐2‐methylpropanesulfonic acid‐co‐butyl methacrylate). This was attributed to the ion exchange between Edrophonium ion and protons produced at the anode. The swelling changes produced by local pH or ionic strength changes affected non‐charged solute release.
Design of target‐specific polymer conjugates and complexes for biomedical application
Authors: Kabanov Victor A. 
Published: March 2011

AbstractThe new effective method of synthesis of protein‐protein and protein‐water soluble linear polymer conjugates based on using of hydrated reversed micelle systems is described. Such conjugates are of a great potential importance in particular for biomedical applications. One example represents a new family of receptor specific screened immunotoxins (respecrins) whose toxic effect develops only with respect to the target but not to the other cells. Respecrin is a toxin covalently bound to a target‐equivalent macromolecule then complexed with an antitarget antibody. Another example relates to artificial immunogenes which are conjugates of antigens or haptenes with non‐natural linear polyelectrolytes. The general mechanism of a search and recognition of target immune cells by such conjugates in vivo was confirmed in model experiments using cell‐mimetic particles. It is also shown that complexing of the DNA plasmide with the carbochain polycation results in formation of membrane active polycomplex much more active in transformation of competent cells than pure plasmide.
Surface modification of polyurethane for enhanced blood compatibility
Authors: Kim Young Ha , Han Dong Keun , Jeong Seo Young , Ahn Kwang‐Duk 
Published: March 2011

AbstractSurfaces of commercial polyurethanes (PUs) were modified by poly(ethylene oxide) (PEO) grafting and/or heparin immobilization or sulfonation to investigate the effect to antithrombogenicity. The hydrophilicity of the modified PUs surface was significantly increased. All the PEO‐grafted PU surfaces displayed very little platelet adhesion and activation. The coupled heparin or sulfonate at the end of PEO exhibited anticoagulant activity to extend APTT. Lowering in vitro platelet adhesion of modified PUs led to a prolongation in the ex vivo occlusion time. In particular, the sulfonated PU‐PEO surface showed the most enhanced blood compatibility due to the synergistic effects of PEO and SO3 groups.
Movement of dopants in redox reaction of electro‐conductive polymers
Authors: Ko J. M. , Rhee H. W. , Kim C. Y. 
Published: March 2011

AbstractPolypyrrole, formed in an organic solvent, shows higher density and better quality in electrical conductivity and mechanical strength than that formed in water. On electrochemical reduction in an aqueous system the laurylsulfate anion, used as dopant, sticks to the polymer. During reduction a cation moves into the polymer and on oxidation it leaves the polymer. The anion, however, leaves the polymer on reduction in an organic solvent system and cannot penetrate into the polymer on re‐oxidation. The redox reaction in the aqueous system reveals a surface reaction process, while the reaction in the organic solvent system undergoes a diffusion‐controlled process. This penomenon is consistant with the results of the ion concentration profile.
The two‐dimensional NMR spectroscopy of macromolecules
Authors: Bovey Frank A. , Mirau Peter A. 
Published: March 2011

AbstractTwo‐dimensional (2D) NMR is a versatile technique which exists in many versions. Two broad classes of 2D techniques are (1) correlated spectroscopy and (2) J‐resolved spectroscopy. The first of these may be divided into two further subdivisions: COSY, which permits correlations of resonances via J‐coupling, and NOESY, which allows direct measurement of intenuclear (usually interproton) distances by the nuclear Overhauser effect. COSY greatly facilitates the interpretation of complex spectra and spectral interpretation in terms of stereochemical sequences is placed on a firmer foundation. NOESY provides direct information concerning the local conformations of polymers in solution. By use of J‐resolved 2D NMR, we can separate J‐couplings and chemical shifts on different axes and thus achieve a degree of resolution of both these parameters far beyond what is attainable in the 1D spectrum. Finally, we may combine correlated and J‐resolved spectroscopy and achieve the benefits of both in 3D NMR, in which the 2D cross peaks exhibit J‐coupling fine structure. These techniques are illustrated for a variety of polymers including poly(methyl methacrylate), poly(vinyl fluoride), poly‐y‐benzyl L‐glutamate, and poly(propylene oxide).
Frequency dependence of nuclear magnetic resonance parameters in poly(methyl methacrylate)
Authors: Chûjǒ Riichirǒ 
Published: March 2011

AbstractUsing 26 NMR spectrometers, the Research Group on NMR, the Society of Polymer Science, Japan observed the 1H NMR chemical shift, resolution, and signal intensity; 13C NMR chemical shift, resolution, and signal intensity; the effect from initiator fragment signal; 1H spin‐lattice relaxation times; 13C spin‐lattice relaxation times; and 13C nuclear Overhauser enhancement of radically polymerized poly(methyl methacrylate). Excellent reliability was found after comparison between the data from different spectrometers. Molecular motion of this polymer was analyzed with a term of 3τ model.
Mesomorphic phases of poly(DI‐n‐alkylsiloxane)s
Authors: Möller Martin , Siffrin Stefan , Kögler Gerhard , Oelfin Dieter 
Published: March 2011

AbstractThe phase behavior of poly(dialkylsiloxane)s which are symmetrically substituted with ethyl, n‐propyl, and n‐butyl side groups has been investigated by solid state NMR and differential scanning calorimetry. All polymers exhibit disordering transitions before isotropization. The observation of conformational and motional changes is correlated to the different thermal transitions. Diffusive rotation of the chain segments around the molecule long axis is indicated by 29Si‐NMR below the isotropization transition. The remarkably fluid character is explained in part by the coexistence of anisotropic and isotropic motional states of the ‐OSiEt2‐ segments. Molecular motion below the upper disordering transition is restricted but still fast with respect to the 29Si‐NMR time scale. Long range reorganization processes have to be considered to explain the difference between α2‐PDES and β2‐PDES. The stepwise disordering at the onset of different motional processes, which results in the formation of a columnar liquid crystalline phase of these highly flexible chain molecules, is discussed with respect to the amphiphilic constitution of the molecules having an inorganic backbone substituted by organic side groups.
Segmental and crosslink point motion in networks
Authors: Dickinson L. C. , Chien J.C.W. , MacKnight W. J. 
Published: March 2011

Abstract13C‐ and 31P‐NMR spin lattice relaxation in the rotating frame have been measured on a series of networks prepared from monodisperse and deliberately bimodal poly(propylene glycols) (PPG) crosslinked with tris(4‐isocyanatophenyl) thiophosphate. The T1pC minima correspond to loss maxima in the DMTA (Dynamic Mechanical Testing) measured at 10Hz. The T1pP minima fall at higher temperatures than those of T1pC for the same network indicating that these crosslinks lag the segments in frequency of motion at a given temperature. The carbon relaxation is biphasic below Tg of the segments indicating two relaxation domains which we assign to bulklike PPG segments and PPG segments proximal to he crosslink. Lineshape analysis by a diffusional model indicates crosslink reorientation is not isotropic until well above Tg. Relaxation and lineshapes for the bimodal networks indicate that junctions are not uniformly plasticized by the segments.
NMR and infrared study of crystalline forms of stereoregular poly(methyl methacrylates)
Authors: Schneider Bohdan , Spêváček Jiří , Straka Jaroslav , Štokr Jan 
Published: March 2011

Abstract13C CP MAS NMR spectra and infrared spectra of amorphous and semicrystalline samples of stereo‐regular poly(methyl methacrylates) were measured. The spectra of the crystalline phases of isotactic PMMA, syndiotactic PMMA and of the so‐called stereocomplex PMMA were obtained by a computer difference technique. These spectra are discussed in relation to the conformational structure of the studied systems.
NMR microscopy ‐ limitations and applications in material sciences ‐
Authors: Kuhn W. , Eichhoff U. 
Published: March 2011

AbstractAlongside the numerous applications of NMR spectroscopy in analytical chemistry, materials sciences and morphological studies by magnetic resonance imaging (MRI), NMR microscopy makes possible a whole new range of applications in materials sciences such as the development and non destructive testing of polymers and ceramic materials. This includes imaging of microscopic structures and structural changes in such materials. The contrast in the images is determined by the NMR specific parameters chemical shift δ, spin density ρ, spin lattice relaxation time T1, spin spin relaxation time T2 and spin lattice relaxation time in the rotating frame T1ρ. The numerous well developed methods available make it possible to study dynamic processes by fast imaging, the measurement of diffusion constants of solvents or liquids, the mobility of fluids in polymers or ceramics or the three dimensional evaluation of pore sizes in porous materials.
Multifrequency ESR and ENDOR studies of ionomers
Authors: Schlick Shulamith 
Published: March 2011

AbstractWe describe methods for determining the local environment of cations and the process of ionic clustering in ionomers, using electron magnetic resonance spectroscopy. The distance between Cu2+ cations in perfluorinated membranes (Nafion) containing terminal sulfonic groups and swollen by water has been deduced from an analysis of ESR spectra at L (1.25 GHz), S (2.36 GHz) and X (9.36 GHz) bands, in membranes containing cupric ion concentrations in the range 1–30 percent of the total amount needed to fully neutralize the pendant acid groups. At higher cation concentrations ESR spectra indicate the presence of aggregated cations. The intercation distance determination is based on the simulation of spectra from isolated cations using distribution widths δg11 and δA11 and extraction of the residual width ΔHR, which is due to dipolar interactions. No aggregation is detected in membranes swollen by less polar solvents such as methanol, dimethylformamide (DMF) and tetrahydrofuran (THF); these results are in contrast to SAXS experiments in membranes swollen by methanol, which exhibit the “ionic peak”. Cu2+‐Cu2+ and Ti3+‐Ti3+ dimers have been detected in Nafion swollen by water, methanol, DMF and THF, and have been characterized by an analysis of the spin‐forbidden half‐field Δms=2 transition, and by computer simulations. The intercation distance in the cupric dimers, deduced from the intensity ratio of the Δms=2 and Δms=1 dimer transitions, is 5.0±0.2 Å. A model for the dimer has been proposed, which explains the crosslinking of the polymer chains by the metal cations. ENDOR signals from 1H, 2H and 19F nuclei have been detected in Nafion neutralized by Ti3+. The ENDOR results allow determination of the local environment of the paramagnetic cations, to a distance of ∼10 Å.
Photoinduced ultrafast processes in phenyl‐substituted poly(phenylenevinylene) s studied by picosecond absorption, fluorescence and conductivity measurements
Authors: Rentsch S. , Yang J. P. , Lenzner M. , Bergner H. 
Published: March 2011

AbstractTransient absorption, fluorescence and conductivity were measured on phenylated poly(phenylenevinylene)s (P‐PPV) in solution and in film after UV pulse excitation in picosecond region. Transient absorption bands of distinguishable rise and decay kinetics were observed. The fluorescence shows two exponential decay times in ps‐ and ns‐region, resp, Transient photoconductivity also exhibits a ps‐ and a ns‐time component. The mobility of carriers was estimated.
Spin dynamics in conducting polymers
Authors: Mizoguchi Kenji 
Published: March 2011

AbstractIt is demonstrated that spin dynamics study is useful for what kinds of systems, on what theoretical basis of analysis, with what kinds of techniques and to get what kinds of information, showing a nice example of polyacetylene. Usefulness of electron spin resonance (ESR) study is stressed especially in a wide frequency range from 5 to 24000 MHz.
Dielectric properties of conducting polymers
Authors: Kremer F. , Rühe J. , Meyer W. H. 
Published: March 2011

AbstractThe frequency and temperature dependence of the complex conductivity σ* is measured for several different conducting polymeric systems: (i) for poly(p‐styrene sulfonate) salts of polypyrrole, (ii) for salts of poly(cycloalkyl[c]pyrroles) and for ion conducting polymers such as ionenes. The results are discussed in terms of a modified Debye‐Hückel‐Falkenhagen theory.