bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and characterization of poly(alkyl vinyl ether)/poly(ϵ‐caprolactone) diblock copolymers
Authors: Verma A. , Glagola M. , Prasad A. , Marand H. , Riffle J. S.
Published: March 2011

This paper reports the synthesis and characterization of hydroxyl functionalized poly(butyl vinyl ether) oligomers, and block copolymers comprised of poly(butyl vinyl ether) and poly(ϵ‐caprolactone). Using the HI/ZnI2 initiating system in toluene at −20°C, monofunctional poly(butyl vinyl ether) oligomers of predicted molecular weights precisely terminated with aldehyde or primary hydroxyl endgroups have been prepared. Furthermore, the primary hydroxyl end functionality has been utilized to initiate ring opening polymerization of ϵ‐caprolactone in the presence of stannous octanoate as the catalyst. This ring opening reaction provides an entry into new poly[(butyl vinyl ether)‐block‐poly(ϵ‐caprolactone)] copolymers.
Kinetics, mechanisms, and synthesis studies of ring‐opening‐closing alternating copolymerization
Authors: Lundmark Stefan , Kobayashi Shiro
Published: March 2011

The present paper describes the ring‐opening‐closing alternating copolymerization of cyclic phosphonites (2‐phenyl‐1,3,2‐dioxaphosphelane (1a), 2‐phenyl‐1,3,2‐dioxaphosphorinane(1b), 2‐phenyl‐1,3,2‐dioxaphosphepane(1c), and 2‐phenyl‐4H‐1,3,2‐benzodioxa phosphorin‐4‐one(1d)) with muconic acid(2a), succinaldehyde(2b), glutaraldehyde(2c), adipinaldehyde(2d), o‐phthalaldehyde(2e), acrylic anhydride(2f), methacrylic anhydride(2g), N‐methyl diacrylamide(2h), and N‐methyldimethacrylamide(2i). The reaction of a 1:1 monomer feed ratio, explained by a mechanism of propagation via zwitterion intermediates, proceeds without any added catalyst to give an alternating copolymer 3 involving ring‐opening of 1 and ring‐closing of 2. The structure of copolymer 3 was determined by1 H,13 C NMR,31 P NMR and IR spectroscopies as well as elemental analysis.
Pd(0) and Ni(0) catalyzed polymerization reactions
Authors: Percec Virgil , Pugh Coleen , Cramer Edwin , Okita Shigeru , Weiss Robert
Published: March 2011

Three novel metal catalyzed cross‐coupling polymerization reactions which result in carbon‐carbon bond formation are described and discussed in context with other metal catalyzed cross‐coupling polymerization reactions. Diarylacetylene monomers and dimers are prepared by the phase transfer Pd(0)/Cu(I) catalyzed coupling of aryl halides with 2‐methyl‐3‐butyn‐2‐ol. Aryl‐alkyl bond forming polymerization reactions are achieved by the phase transfer Pd(0) catalyzed coupling of B‐alkyl‐9‐borabicyclo[3.3.1]nonane derivatives with aryl halides. Soluble polyphenylenes are prepared by the Ni(0) catalyzed homocoupling of substituted phenylenebistriflates in the presence of zinc.
New palladium‐ and nickel‐catalyzed polycondensations for synthesis of carbon‐carbon chain polymers, polyamides, and related condensation polymers
Authors: Imai Yoshio
Published: March 2011

This article reviews our current work on the palladium‐ and nickel‐catalyzed polycondensations for the synthesis of various types of condensation polymers. We succeeded for the first time in the synthesis of carbon‐carbon coupling polymers, that is polycinnamamides, by the palladium‐catalyzed cross‐coupling polycondensation of aromatic diiodides with divinylic compounds. We further developed a new promising method of the synthesis of aramids and related condensation polymers by the palladium‐catalyzed carbonylation polycondensation starting from aromatic dibromides, bifunctional nucleophilic monomers such as aromatic diamines, and carbon monoxide.
Novel platinum initiators for ring‐opening polymerizations
Authors: Crivello James V. , Fan Mingxin
Published: March 2011

Platinum complexes together with compounds containing silicon‐hydrogen bonds comprise a novel class of initiators for the ring‐opening polymerization of a wide variety of heterocyclic compounds including; epoxides, oxetanes and 1,3,5‐trioxane. This paper reports on a preliminary survey of the scope and limitations of these new initiator systems with special emphasis on the ring‐opening polymerization of epoxides. Considerable effort has been directed towards the elucidation of the mechanism of the polymerizations initiated by these systems. The best current evidence suggests that polymerization proceeds by a cationic mechanism. Data is also presented which suggests that platinum metal colloids may function as the active initiating species.
Regioselective ring‐opening polymerizations and hydrosilations catalyzed by transition metals
Authors: Crivello James V. , Fan Mingxin
Published: March 2011

Organometallic rhodium complexes were found to be catalysts for the ring‐opening polymerization of epoxides and other heterocyclic compounds. A cocatalyst, consisting of a compound or polymer containing silicon‐hydrogen bonds is also required. These same catalyst‐cocatalyst mixtures are also highly active for hydrosilation reactions. Rhodium phosphine complexes have been discovered which, while active for hydrosilation, are not catalysts for epoxide polymerizations. These rhodium phosphine complexes permit the synthesis of epoxy‐functional silanes and siloxanes in high yields without competing ring‐opening polymerization.
Mechanisms of the aromatic polyetherification reactions
Authors: Percec Virgil , Wang James H. , Clough Robert S.
Published: March 2011

The mechanisms of aromatic nucleophilic substitutions are briefly reviewed with emphasis on those which have been used for the synthesis of aromatic polyethers and aromatic polythioethers, i.e. the SNAr, the SRN1, and a variant of SRN1 (the SRN1′) mechanisms. The synthesis of poly(ether ketone)s by the SNAr mechanism is discussed in terms of polar versus the single electron transfer (SET) pathways. The synthesis of poly(2,6‐dimethyl‐1,4‐phenylene ether) (PPE) by the phase transfer catalyzed (PTC) anion‐radical mechanism (i.e. the SRN1′ mechanism) is discussed in comparison with the synthesis of PPE by the conventional radical‐radical mechanism. Various examples of the PTC copolymerization of 4‐bromo‐2,6‐dimethylphenol with a phenol comonomer are provided. These PTC copolymerization experiments led to the synthesis of PPE with well‐defined chain end functionalities and controlled molecular weights. The PTC depolymerization of high molecular weight PPE terminated with a 2,6‐dimethylphenol chain end in the presence of a phenol is discussed. The depolymerization proceeds by an anion‐radical mechanism.
New activating groups for poly(aryl ether) synthesis
Authors: Labadie J. W. , Hedrick J. L.
Published: March 2011

We have investigated new activating groups for poly(aryl ether) synthesis and have demonstrated that quinoxaline, benzazole, amide, and perfluoroalkyl groups activate fluoro‐ and, in some cases, nitro‐displacements from aromatic rings. The quinoxaline‐activated aryl ether synthesis involved activation by the electron deficient pyrazine ring of the 6‐position on the fused benzo ring. Thiophenoxides displaced 6‐chloro and 6‐nitro groups from quinoxalines under milder conditions than required for the ether synthesis. Pendent benzoxazole, benzothiazole, and amide groups activated displacement of a para fluoro group in high yield and selectivity. Perfluoroalkyl groups activated 2‐ and 4‐fluoro or nitro groups towards displacement, presumably by stabilization of the transition state through hyperconjugation. The new transformations were utilized for the synthesis of high molecular weight heterocyclic, amide and perfluoroalkyl‐based poly(aryl ethers). The resulting polymers were amorphous and displayed distinct glass transition temperatures, as well as improved solution and melt processability.
Synthesis of aromatic polyethers by cation‐radical polymerization
Authors: Percec Virgil , Wang James H.
Published: March 2011

This paper discusses the synthesis of aromatic polyethers including poly(ether sulfone)s, poly(ether ether ketone)s, fully aromatic polyethers and polyarylenes by the cation‐radical polymerization (Scholl reaction) of bisaryl monomers. The polymerizability of various monomers is discussed with respect to the effects of the monomer structure on the reactivity of both the monomers and of the cation‐radical growing species. Examples are provided for the synthesis of polymers of unique structure by the cation‐radical polymerization reactions. The cation‐radical polymerization reactions have been studied under a variety of experimental conditions. The oxidants used as initiators include various Lewis acids and their combinations such as FeCl3, AlCl3/CuCl2, AlCl3/CuCl/O2, AlCl3/FeCl3, FeCl3:tris(3,6‐dioxaheptyl)amine complex, and organic electron‐acceptor compounds such as 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone (DDQ). This polymerization proceeds in electrophilic solvents such as nitrobenzene, methylene chloride, etc. The cation‐radical polymerization initiated by a catalytic amount of oxidant is demonstrated by using vanadyl acetylacetonate as oxidant. An example in which the polymerization proceeds by both a cation‐radical reaction and an electrophilic transalkylation reaction is provided by the polymerization of 2,2‐bis[4‐(1‐naphthoxy)phenyl]propane initiated with FeCl3.
Polyphthalazines and polyisoquinolines with rigid‐rod‐like structures
Authors: Singh Rina , Hay Allan S.
Published: March 2011

The synthesis of new classes of N‐heterocyclic polymers, the polyisoquinolines and polyphthalazines are described from intramolecular ring closure reactions of a novel aromatic polyketone. The polyketone was synthesized by the nickel‐catalyzed coupling reaction of 1,2‐bis(4‐chlorobenzoyl)‐3,6‐diphenylbenzene. The thermal and mechanical properties of the N‐heterocyclics synthesized from the polyketone are compared to analogous N‐heterocyclics containing flexible linkages synthesized from poly(ether ketone)s containing ortho‐dibenzoylbenzene moieties.
Polycondensation of silylated monomers
Authors: Kricheldorf Hans R.
Published: March 2011

Various polycondensations of silylated aromatic monomers, such as aminophenols, diphenols, hydroxy acids, dicarboxylic acids or acetoxybenzoic acids are reported. Reaction mechanisms and preparative usefulness of their polycondensations are discussed. In this connection also structure/property relationships of aromatic polyethers, liquid‐crystalline polyesters and poly‐(ester‐anhydride)s are mentioned.
New step growth polymers via reissert compound chemistry
Authors: Gibson Harry W. , Pandya Ashish , Rasco Melvin L. , Guilani Bardia , Hermann Christine K. F. , Leblanc Jean‐Pierre , Jois Yajnanarayana H. R.
Published: March 2011

Reissert compounds are the result of the formal addition of acyl cyanides across the CH=N bonds of aromatic heterocyclic compounds or acyclic imines. The chemistry of this class of compounds is primarily based upon the acidity of the CH(CN)‐NCOR moiety and the nucleophilic reactivity of the conjugate base. Three methodologies for application of this chemistry to the synthesis of polymers are summarized: 1) formation of polyamides by the “Reissert reaction” of suitable difunctional imines and diacid chlorides, 2) condensation of the anions of difunctional Reissert compounds with dielectrophiles such as dihaloalkanes and dialdehydes and 3) use of Reissert compound chemistry to construct novel monomers for use in traditional condensation polymerizations. All three methodologies are proven to be effective in the production of nitrogen containing polymers.
Poly(enaminonitriles) containing biphenyl and terphenyl units in the main chain
Authors: Moore J. A. , Kim Sang Youl
Published: March 2011

Two new monomers, 4,4′‐bis(1‐chloro‐2,2‐dicyanovinyl)biphenyl and 4,4″‐bis(1‐chloro‐2,2‐dicyanovinyl)‐p‐terphenyl, have been synthesized and polymerized with several diamines by vinylic nucleophilic substitution producing poly(enaminonitriles) with molecular weight varying from low to moderately high, depending on the diamines used. The polymers were soluble in polar, aprotic solvents before thermal curing, but became insoluble at high temperatures without the evolution of volatile byproducts. These new polymers exhibit excellent thermal stability, particularly when they contain para‐linked aromatic rings. Dielectric measurements of some of the polymers revealed dielectric constants of at least 4.
Self‐assembling synthetic supramolecular polymers
Authors: Ashton Peter R. , Philp Douglas , Spencer Neil , Stoddart J. Fraser
Published: March 2011

The solid state structure of a [2]catenane, composed of macrocyclic rings containing π‐electron rich hydroquinol rings and π‐electron deficient bipyridinium units has revealed an approach to the elaboration of supramolecular polymers with a double helical tertiary structure. Neutral molecules containing up to five hydroquinol rings, separated by trioxaundecane spacers and terminated by benzyl ether functions, have been shown by 1H NMR spectroscopy to form superstructures with possible double helical character as a result of π‐π stacking and other non‐covalent bonding interactions with polycations containing up to four bipyridinium units separated by p‐xylyl spacers and terminated also by benzyl functions.
Design of novel structurally defined ladder‐type polymers
Authors: Fahnenstich U. , Koch K.‐H. , Pollmann M. , Scherf U. , Wagner M. , Wegener S. , Müllen K.
Published: March 2011

Two different approaches for the synthesis of structurally defined ladder‐type polymers are described. Repetitive Diels‐Alder reaction as well as polymer analogous cyclization of suitable open‐chain precursors are used for generating novel band‐type structures. Polymeric [2.2]‐cyclophanes and ethene‐bridged polyacene precursors are prepared via [4 + 2] cycloaddition reactions. Ladder‐type poly(p‐phenylene) and oligo(perinaphthylenes) as planar π‐systems are obtained by Friedel‐Crafts‐ rsp. by alkali‐metal induced electrocyclic ring‐closure reactions.
Hypercrosslinked rigid‐rod polymers
Authors: Webster O. W. , Gentry F. P. , Farlee R. D. , Smart B. E.
Published: March 2011

In a search for new types of polymer architecture, we have examined systems where one couples rigid‐rod monomers with multifunctional tie‐point monomers. High surface area (400–1000 m2/g) polymeric carbinols result from reaction of 4,4′‐dilithiobiphenyl, as well as other multi‐lithiated aromatic compounds with dimethyl carbonate.
Polymers tailored for redox‐ and photoactivity
Authors: Bartz Thomas , Böhm Arno , Klapper Markus , Müllen Klaus , Weitzel Hans‐Peter
Published: March 2011

The synthesis of polymers tailored for a specific redox‐ and photoactivity is described.

The title compounds can generally be depicted as consisting of electrophoric or chromophoric building blocks which are linked by variable bridging groups.

Their properties depend on the nature of both units in the polymer chain. The bridging group between the electrophoric units can be saturated or conjugated and can be incorporated directly upon polymer formation. However, in other polymers such bridging groups are already present, which allow one to switch between an unsaturated and saturated linking.

With the “reductive polymerization”, a new method to link e.g. anthracene and isopyrene units is proposed. A Heck‐type reaction and the boronic acid coupling according to Suzuki are used for generating conjugated polymers.

In the case of polymers containing 2,2′‐distyrylbiphenyl units it is possible to interrupt π‐conjugation via electron‐transfer or UV‐irradiation. With a thermal ring‐opening reaction of cyclobutene units, a method is shown to create conjugation between π‐systems. By hydrogen elimination in a polymethide structure highly conjugated polymers can be created.
Enzymatic polymerization: The first in vitro synthesis of cellulose via nonbiosynthetic path catalyzed by cellulase
Authors: Kobayashi Shiro , Kashiwa Keita , Shimada Junji , Kawasaki Tatsuya , Shoda Shin‐ichiro
Published: March 2011

The in vitro synthesis of cellulose via a nonbiosynthetic path has been achieved for the first time by condensation of β‐D‐cellobiosyl fluoride as substrate for cellulase in a mixed solvent of acetonitrile/acetate buffer (pH 5,5:1) (enzymatic polymerization). Under reaction condition of a higher substrate concentration or higher acetonitrile concentration, cellooligosaccharides were produced predominantly. The present method of using a glycosyl fluoride as substrate for a hydrolytic enzyme in an organic/water mixed solvent has successfully been applied to synthesis of maltooligosaccharides and unnatural oligosaccharides.
Copolymerization of methacryloyl‐terminated PMMA macromonomers with methyl methacrylate
Authors: Radke Wolfgang , Müller Axel H. E.
Published: March 2011

Methacryloyl‐terminated macromonomers (MM) of polymethylmethacrylate (PMMA) of two different molecular weights were prepared by group transfer polymerization (GTP). They were copolymerized with methyl methacrylate (MMA) by radical polymerization using toluene as the solvent. The relative reactivity of the MM, 1/r1, decreases with increasing initial MM concentration. This is interpreted as a consequence of the increasing viscosity of the reaction medium leading to an increasing diffusion control of the MM addition. At a constant weight ratio of MMA to MM the reactivity of the longer macromonomer is higher than of the shorter one. Increasing the molar ratio [MMA]/[MM], i.e. increasing the average distance between two grafts in the resulting comb polymer, increases the reactivity of the MM. These results are interpreted on the basis of a model describing the segment density in the vicinity of the radical chain end of the comb polymer.
The mechanism of plasma‐induced polymerization
Authors: Simionescu Cristofor I. , Simionescu Bogdan C.
Published: March 2011

The paper is concerned with the discussion of the different mechanisms proposed for plasma‐induced (initiated) polymerization. This new approach to polymer synthesis proceeds through a free radical mechanism, but presents some peculiar characteristics. The initiation reaction is practically instantaneous and the activity of the propagating chains appears to be unusually high and very stable in time.
Mechanism and microstructure in the free‐radical polymerization of vinyl chloride: Head‐to‐head addition revisited
Authors: Starnes W. H. , Wojciechowski B. J.
Published: March 2011

The recent realization that 1,2‐dichloroethyl branches occur in poly(vinyl chloride) (PVC) has now led to a full description of the chemical consequences of head‐to‐head addition during the free‐radical polymerization of vinyl chloride (VC). A kinetic analysis of the relevant reaction scheme is developed here and then verified with the aid of literature values for the branch concentrations of PVC samples prepared by polymerization at subsaturation VC pressures. The analysis allows the following conclusions to be drawn: (1) Kinetically free chlorine atoms are not formed from polymeric ‐CHCl‐CH‐CH2Cl or ‐CH2‐CH‐CHCl‐CH2Cl radicals. Loss of chlorine from these radicals results exclusively, instead, from β scission reactions that transfer chlorine directly to the monomer and are kinetically second‐order, overall. (2) The monomer transfer constant that pertains to the transfer occurring after head‐to‐head addition is, indeed, a true constant that is independent of the concentration of VC. (3) In conventional bulk or suspension VC polymerizations, the rates of the propagation reactions are not controlled by diffusion, even at conversions of ca. 90%. (4) A second type of monomer transfer process probably is responsible for the reductions in polymer molecular weight that result from polymerization at subsaturation VC pressures. This transfer pathway involves the inter‐ and/or intramolecular abstraction of methylene hydrogen from the polymer by the ordinary head‐to‐tail macroradicals. The resultant β‐chloroalkyl radicals then transfer chlorine to VC by β scission.
Cooperativity and chirality in a wormlike helical macromolecule
Authors: Green Mark M. , Peterson Norman C. , Lifson Shneior , Sato Takahiro , Teramoto Akio
Published: March 2011

A question about broken rods and worms concerning the dimensional characteristics of poly(alkyl isocyanates) led to the discovery of an extreme sensitivity of this polymer class to tiny chiral perturbations. There is a cooperative source of this phenomenon and statistical thermodynamic methods allow quantitative expression to the forces at work. From this effort we could answer the original question and also extend these ideas into the area of lyotropic liquid crystals where the interplay of macromolecular and supramolecular helicity seems to play by the same rules.
Synthesis and characterization of thermotropic polyester‐block‐polyethers
Authors: Thuillier Pascal , Tessier Martine , Maréchal Ernest
Published: March 2011

Polyester‐block‐polyethers with rigid thermotropic polyarylate blocks are prepared and studied. Rigid polyarylates are poly(1,5‐pentanediyl 4,4′‐biphenyl‐dicarboxylate) or poly(1,5‐pentanediyl 4,4′‐trans‐stilbenedicarboxylate). Flexible blocks are oligo(oxytetramethylene)s (M̄n = 620 or 2030). The block copolymers are characterized by 1H and 13C NMR spectroscopies. The use of 500 MHz 1H NMR permits their complete structural analysis showing that they contain a cyclic oligomer. SEC, polarizing microscopy and X‐ray studies show that their mesophase is smectic. Their viscoelastic properties are compared to those of some aromatic polyester‐block‐polyethers.
Novel organoboron polymers hydroboration polymerization and haloboration polymerization
Authors: Chujo Y. , Tomita I. , Saegusa T.
Published: March 2011

As a novel methodology for the preparation of organoboron polymers, this paper describes “hydroboration polymerization” and “haloboration polymerization”. A polyaddition between diene and tert‐hexylborane (thexylborane) produced a polymer consisting of C‐B bonds in the main chain. The resulting organoboron polymers can be regarded as a polymer homologue of trialkylborane and can be expected as a novel type of reactive polymers. For example, the reaction of organoboron polymer with carbon monoxide followed by the oxidative treatment produced a polyalcohol by the migration of C‐B bonds. Similarly, the reaction with potassium cyanide produced a polyketone. On the other hand, hydroboration polymerization of dicyano compounds such as isophthalonitrile with t‐butylborane produced an air‐stable boron‐containing polymer (polycyclodiborazane) having B‐N four‐membered rings via dimerization of iminoborane species. In haloboration polymerization, i.e., a polyaddition between diacetylene and boron tribromide, a linear poly(organoboron halide) was obtained. This polymer still has B‐Br bonds in its structure and was used not only as a novel reactive polymer but also as a polymeric Lewis acid.
Stereospecific living polymerization and copolymerization of methacrylate and their use for construction of stereoregular chain architecture
Authors: Hatada Koichi , Kitayama Tatsuki , Ute Koichi
Published: March 2011

Highly isotactic and highly syndiotactic living polymerizations of alkyl methacrylates were carried out in toluene at low temperatures by t‐C4H9MgBr and t‐C4H9Li‐R3A1, respectively. These living polymerizations enabled us to prepare highly stereoregular block and random copolymers of methacrylates with narrow molecular weight distributions. Reaction of ethylene glycol dimethacrylate with isotactic PMMA anion gave a highly branched star polymer. Syndiotactic PMMA star polymer was prepared by similar method. Stereoregular PMMA macromonomers with styrene and methacryloyl functions were prepared by using the stereospecific living polymerizations and polymerized by radical and anionic mechanisms. It was found that isotactic PMMA formed stereocomplexes with various types of syndiotactic polymethacrylates when treated under certain conditions. The complexes showed melting points which differ in a wide range of temperature. Isotactic and syndiotactic MMA oligomers without molecular weight distribution were isolated by supercritical fluid chromatography up to 29‐mer and characterized.
Studies on enolate‐initiated polymerisation
Authors: Jenkins Aubrey D.
Published: March 2011

Initiation of anionic polymerisation by means of enolate ions has many advantages. It has been applied to the synthesis of macromolecules with specific structures, e.g. graft and block polymers, and H‐polymers. Its application to dispersion polymerisation is also reported.
Molecular architecture control in acrylic polymers by group transfer polymerization
Authors: Webster Owen W.
Published: March 2011

Group transfer polymerization (GTP)a of acrylic monomers is mediated by a trialkylsilyl‐capped growing chain end. It operates at room temperature and above and permits a high degree of molecular architecture control. Block, comb, graft, star, and loop polymers are readily synthesized. It appears that GTP is an associative process under mild nucleophilic catalysis and a dissociative process under strong nucleophilic catalysis.
Folded chain crystallization of thermotropic, random terpolymer, main chain liquid crystal polymers
Authors: Kent S. L. , Geil P. H.
Published: March 2011

Single crystals, suitable for electron microscopy and diffraction, have been grown from the quiescent and sheared “liquid crystal” state and solution for several random terpolymer polyesters having a nearly equimolar amount of a flexible segment dicarboxylate (4–7 CH2), oxybenzoate and dioxyphenyl. In all cases, in thin films and on free surfaces, folded chain lamellae are observed. High temperature electron diffraction has permitted characterization of the transition behavior and structure of the liquid crystal state. Permanganate etching permitted characterization of the interior of molded, extruded or spun samples; in these cases extended chain lamellae are observed. The results suggest chain folding in the nematic state at least in the thin films and on surfaces, with chain folding also possible in the bulk followed by chain extension by “sliding” diffusion.
Phase separation in bulk statistical copolymers and their mixtures with homopolymers. I. Theory
Authors: šolc K.
Published: March 2011

A method based on the Flory‐Huggins thermodynamics is presented for modeling phase equilibria in bulk statistical copolymers of two monomers. For a given phase separation, a component's preference for one of the phases depends only on its composition, and there always exists a balanced composition which shows no preference at all and assumes equal concentrations in both phases. In contrast, the degree of enrichment depends exponentially on the component's chain length and the magnitude of the deviation of its composition from the balanced one. A fast two‐loop iteration scheme is devised for numerical computation of phase equilibria for any distribution of chain length and composition. Critical state formulas can be cast succintly in terms of averages of deviations from the balanced composition (which here equals the z‐average composition). At the critical composition, the (z+1)‐average of cubed deviations has to be zero, whereas the critical value of the interaction parameter is inversely proportional to the z‐average of squared deviations and to the w‐average chain length. Thus, e.g., a copolymer with a symmetrical distribution always constitutes a critical mixture.
Polymer microspheres as carriers of the immobilized enzymes
Authors: Hayashi Toshio
Published: March 2011

In this paper, after an outline of the nature and methods of the immobilization of enzymes, some properties of covalently immobilized enzyme, such as enzymic activity, stability and specificity, will be discussed with experimental results obtained by us. Papain is selected as a model of hydrolytic enzymes, and polymer supports employed are polyacrolein microspheres, porous beads of chitosan, and poly(γ‐methyl‐L‐glutamate). The effect of spacer on the activity and stability of covalently immobilized enzyme is also considered.
Polymeric drugs as immunomodulatory vaccines against multiple sclerosis
Authors: Sela Michael
Published: March 2011

COP‐1, a synthetic basic random amino acid copolymer, is effective in suppression of experimental allergic encephalomyelitis in guinea pigs, rabbits, mice, rhesus monkeys and baboons, and of the exacerbating‐remitting type of multiple sclerosis in humans. COP‐1 is cross‐reactive at the monoclonal antibody level with the basic protein of the myelin sheath of the brain (BP), and the suppressive effect may be related to this immunological cross‐reaction. Indeed, competition for the major histocompatibility complex (MHC) class II antigen, between BP and COP‐1, may be one explanation for its beneficial effect in the disease. This polymeric drug, COP‐1, may, therefore, be considered also an immunomodulatory vaccine, and may serve as a prototype to vaccines against autoimmune diseases.
Development of N‐(2‐hydroxypropyl)methacrylamide copolymer conjugates for delivery of cancer chemotherapy
Authors: Duncan Ruth , Ulbrich Karel
Published: March 2011

In recent years a series of N‐(2‐hydroxypropyl)methacrylamide (HPMA) copolymers have been synthesised containing antitumour agents, particularly doxorubicin (Dox) bound to the polymer carrier by peptidyl spacers designed for cleavage by lysosomal thiol‐dependent proteases, enzymes known to show increased activity in metastatic tumours. Such conjugates display a broad range of antitumour activities against leukaemic, solid tumour and metastatic models, and recent experimentation has focussed on investigating further their mechanism of action. It is believed that drug conjugation leads to reduced toxicity, passive accumulation within solid tumours due to the enhanced permeability and retention effect and subsequent controlled drug release. All these factors contribute to the improved antitumour activity seen.
Nonlinear dielectric and conductive spectra of polymers
Authors: Furukawa Takeo
Published: March 2011

Nonlinear complex permittivities have been measured as a function of frequency for various polar polymers by applying a sinusoidal electric field and detecting higher harmonic dielectric responses. It is shown that the Debye relaxation of the linear permittivity accompanies the third‐order nonlinear relaxation represented by ϵ3*=δϵ3/(1+iωϵ3)3 in accord with phenomenological prediction. Combinations of relaxation strengths, δϵ1 and δϵ3, allow estimates of the saturation polarization as well as the moment and density of equivalent dipoles comprising the relaxation process. Analogous measurements and analysis have been extended to examine the nonlinear conductive spectra of ion‐conducting polymers.
Controlling the mechanical performance of composites
Authors: Vu‐Khanh T.
Published: March 2011

There are presently several models based on different assumptions out of which one may find one to predict the elastic properties of a given type of composite. However, there is not a single theory which can be used to model all systems. One of the difficulties encountered in verifying the proposed models is the non‐uniformity of the dimension, distribution, shape, and orientation of the reinforcement, resulting from the processing conditions of the composite in practice. Much work has been carried out in an effort to express theoretically the strength and stiffness of composites. In spite of extensive investigation efforts, prediction is still a controversial subject. Unlike the elastic properties, which involve only small deformations without irreversible processes, fracture performance depends on many parameters. Besides the reinforcement dimension, shape and orientation, the interfacial adhesion and the microscopic failure mechanisms also play major roles in both strength and toughness.
Elastomers and thermoplastics as modifiers for thermosetting resins
Authors: Bucknall C. B. , Maïstros G. , Gomez C. M. , Partridge I. K.
Published: March 2011

Factors affecting mixing and demixing from solutions of thermoplastics and elastomers in epoxy resin are discussed, and related to morphology; dielectric monitoring is used to follow phase separation in curing elastomer blends. Mechanisms of toughening are related to morphology.
Polymer grafted on porous silica as supports for catalysts and reagents
Authors: Guyot A. , Revillon A. , Carlier E. , Leroux D. , Le Deore C.
Published: March 2011

The main part of the paper is dealing with 4 routes used to anchor chloromethyl groups to polymer grafted onto porous silica. The most efficient route involves first, grafting of a coupling agent bearing one function active in radical polymerization as initiator, comonomer or transfer agent, and then polymerization of vinylbenzyl chloride. The grafting efficiency, the homogeneity of the grafting process and the conformation of the grafted polymer are discussed, depending on the experimental conditions. Other grafted polymers are 1,2‐polybutadiene and poly(phenylsiloxane). For catalytic applications, chloromethyl groups are reacted with ephedrin and the resulting solid is used for benzaldehyde alkylation with diethylzinc. On the other hand, grafted poly(phenylsiloxane) is sulfonated and used for esterification and phenol alkylation by dodecene.
Synthesis and characterisation of porous polymers
Authors: Sherrington D. C.
Published: March 2011

State‐of‐the‐art electron microscopic studies have been made of the ultrastructure of a matrix of specifically prepared styrene‐divinylbenzene resin sorbents. Image analysis methods have been applied to quantify the porous morphology of these resins in the “dry”, “freeze‐dried” and “frozen” states. Significant swelling has been demonstrated in the wet state. Highly porous Polyhipe® monoliths have been prepared and used to produce a polyamide‐impregnated composite support for use in solid phase synthesis of peptides. The composite shows good pressure resistance and allows high yields of pure peptides to be achieved. Polyhipe® polymers with very high surface areas (up to 350 m2g−1) have been prepared by applying the methodologies of porous particulate resin production to achieve highly porous walls in the Polyhipe® structures. Finally, novel procedures are described for the preparation of porous particulate polyimides and polybenzimidazoles involving a paraffin oil dispersion methodology. These thermooxidatively stable resins have been prepared with modest surface areas of ∼30 m2g−1 and offer good prospects for use as supports for alkene transition metal complex oxidation catalysts.
Progress in catalytic membrane systems
Authors: Drioli Enrico , Molinari Raffaele , Basile Angelo
Published: March 2011

The importance of polymeric materials for preparing different kinds of membranes to be used in catalytic systems is reported. Various polymer‐based membrane reactors and their performance in applications of industrial interest are reviewed.
Application of ion‐exchange membranes in industrial processes
Authors: Strathmann H.
Published: March 2011

Ion‐exchange membranes are used on a large scale in many commercially relevant processes such as in electrolytical and electrodialytical procedures as well as in energy conversion or storage systems. The discussion in this paper, however, is concentrated on processes using ion‐exchange membranes in mass separation. The basic concept of the processes and their advantages as well as intrinsic limitations are discussed. Processes using ion‐exchange membranes in water treatment as well as in the chemical and food industry are described in selected examples and recent improvements in membrane products and process performance are discussed.
Transport of gases through polymeric membranes
Authors: Wessling M. , Boomgaard T.v.d. , Mulder M.H.V. , Smolders C. A.
Published: March 2011

In this paper tailor‐made polymers like polyoxadiazoles, polytriazoles and polyimides are compared with conventional polymers as gas separation membrane materials. Because their permeation characteristics as a function of the free volume does not compare too well with that of the conventional ones the term free volume was reconsidered. Based on a unique relation between the diffusion coefficient and the jump of the heat capacity at the glass transition temperature Tg, the transport mechanism in the polymer matrix is considered to occur in jump motions from one cavity to an adjacent one. This mechanism was reconfirmed by a molecular dynamics study. It is shown that mass transport at high penetrant concentrations is not time‐independent but a phenomenon with transient characteristics. This transient character is also found in the volumetric behaviour during sorption. The polymer matrix is described as a network with topological constraints which changes its state upon high swelling stresses induced by the sorbed penetrant.
New trends of membrane separation technology
Authors: Kimura Shoji
Published: March 2011

For separation of various organic ‐ aqueous mixtures and organic‐organic mixtures, there are three possible membrane separation technologies, namely, reverse osmosis(RO), pervaporation(PV) and vapor permeation(VP). A theoretical comparison is introduced. Using various membranes experimental data are demonstrated for varieties of such systems. Finally one example method to design a suitable membrane for a particular system is demonstrated.
High‐molecular‐weight ultraviolet stabilizers for plastics
Authors: Minagawa Motonobu , Kikkawa Kazumi
Published: March 2011

The effect of molecular weight (MW) of ultraviolet (UV) stabilizers (hindered amine light stabilizers and ultraviolet absorbers) on performance in plastics are discussed. There exists an optimum MW for them, which may change with test conditions, applications and so forth. Recent new trends in plastics used in automobile (higher temperature processing, the use of easily recyclable plastics and upgrading their durability) seem to move the optimum MW for UV stabilizers to higher ones. The future of high‐molecular‐weight UV stabilizers (oligomeric and polymer‐bound) are surveyed in connection with their higher performance due to lower volatility and higher retention in plastics.
Thermal and photooxidative studies of polyethylene
Authors: Bigger Stephen W. , Scheirs John , Delatycki Oskar
Published: March 2011

The technique of oxygen uptake measurement for assessing the photo‐ and thermal stability of polyethylene is reviewed. An oxygen uptake apparatus is described which was used to determine the thermooxidative stabilities of nascent, high‐density polyethylenes produced by Ziegler‐Natta, and silica‐supported “silyl chromate” and “chromocene” catalyst systems. The oxygen uptake results are compared with those obtained from the thermochemical technique of differential scanning calorimetry.
Effect of treated filler on the compatibility of poly(methyl methacrylate) / polystyrene blends
Authors: Scherbakoff Natalia , Ishida Hatsuo
Published: March 2011

This work describes a new approach for compatibilizing immiscible polymer blends by fillers. The polystyrene ‐ poly(methyl methacrylate) ‐ glass beads is the studied system. The role of the silane‐treated and non‐treated filler surface on the compatibilization process of this immiscible blend has been evaluated by dynamic mechanical spectrometry, scanning electron microscopy and size exclusion chromatography. The observed changes in morphology are correlated with the enhancement of the interfacial adhesion between polymer/filler and polymer/polymer.
On the relationship between seed‐based and ICA‐based measures of functional connectivity
Authors: Joel Suresh E. , Caffo Brian S. , van Zijl Peter C. M. , Pekar James J.
Published: March 2011

Brain functional connectivity (FC) refers to inter‐regional synchrony of low frequency fluctuations in blood oxygenation level dependent functional magnetic resonance imaging. FC has been evaluated both during task performance and in the “resting” state, yielding reports of FC differences correlated with behavior and diagnosis. Two methodologies are widely used for evaluating FC from blood oxygenation level dependent functional magnetic resonance imaging data: Temporal correlation with a specified seed voxel or small region of interest; and spatial independent component analysis. While results from seed‐based and independent component analysis methodologies are generally similar, they are conceptually different. This study is intended to elucidate and illustrate, qualitatively and quantitatively, the relationship between seed and independent component analysis derived measures of FC. Seed‐based FC measures are shown to be the sum of independent component analysis‐derived within network connectivities and between network connectivities. We present a simple simulation and an experiment on visuomotor activity that highlight this relationship between the two methods. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.
Saturation power dependence of amide proton transfer image contrasts in human brain tumors and strokes at 3 T
Authors: Zhao Xuna , Wen Zhibo , Huang Fanheng , Lu Shilong , Wang Xianlong , Hu Shuguang , Zu Donglin , Zhou Jinyuan
Published: March 2011

Amide proton transfer (APT) imaging is capable of detecting mobile cellular proteins and peptides in tumor and monitoring pH effects in stroke, through the saturation transfer between irradiated amide protons and water protons. In this work, four healthy subjects, eight brain tumor patients (four with high‐grade glioma, one with lung cancer metastasis, and three with meningioma), and four stroke patients (average 4.3 ± 2.5 days after the onset of the stroke) were scanned at 3 T, using different radiofrequency saturation powers. The APT effect was quantified using the magnetization transfer ratio (MTR) asymmetry at 3.5 ppm with respect to the water resonance. At a saturation power of 2 μT, the measured APT‐MRI signal of the normal brain tissue was almost zero, due to the contamination of the negative conventional magnetization transfer ratio asymmetry. This irradiation power caused an optimal hyperintense APT‐MRI signal in the tumor and an optimal hypointense signal in the stroke, compared to the normal brain tissue. The results suggest that the saturation power of 2 μT is ideal for APT imaging of these two pathologies at 3 T with the existing clinical hardware. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.
Early initiation of toilet training for urine was associated with early urinary continence and does not appear to be associated with bladder dysfunction
Authors: Yang Stephen Shei‐Dei , Zhao Lu‐Lu , Chang Shang‐Jen
Published: March 2011

Objective

To report the relationship between the ages initiating toilet training for urinary continence (TTU) and bladder function in healthy kindergarteners.

Patients and Methods

In 3 years, we evaluated urinary continence status and bladder function in 318 healthy kindergarteners. Children with congenital anomaly, neurological disorder, or developmental disability were excluded. A parent completed the questionnaire including the age at initiation and the duration of TTU, the current status of daytime and nighttime continence, the age of attaining daytime and nighttime continence, frequency of defecation and Bristol Stool Scale. All children underwent uroflowmetry and post‐void residual urine (PVR) examinations.

Results

Finally, 235 respondents (106 boys/129 girls, mean age = 4.8 ± 0.9 years) were eligible for analysis. The mean age initiating TTU was 24.4 ± 8.4 months (range: 1–52 months). Girls started TTU earlier than boys (23.3 months vs. 25.7 months, P = 0.03). Children started daytime TTU earlier (≤18, 19–24, and >24 months, N = 66, 71, and 98, respectively) was associated with earlier attainment of both daytime and nighttime continence (correlation coefficient = 0.60 and 0.31, respectively, P < 0.01). Children started nighttime TTU earlier (<30 months vs. ≥30 months) was associated with early attainment of nighttime continence and lower rate of enuresis (14.3% vs. 33.3%, P < 0.01). The prevalence rate of repeat abnormal uroflow patterns and repeat elevated PVR (>20 ml) was not different between early and late TTU.

Conclusion

Early toilet training for urine was associated with early attainment of both daytime and nighttime urinary continence, and does not appear to be associated with bladder dysfunction. Neurourol. Urodynam. 30:1253–1257, 2011. © 2011 Wiley‐Liss, Inc.
Investigation of optimal cues to instruction for pelvic floor muscle contraction: A pilot study using 2D ultrasound imaging in pre‐menopausal, nulliparous, continent women
Authors: Crotty Kay , Bartram Clive I. , Pitkin Joan , Cairns Mindy C. , Taylor Paul C. , Dorey Grace , Chatoor Dave
Published: March 2011

Aims

Optimal urethrovesical positioning (UVP) may be important for continence. Pelvic floor muscle contraction (PFMC) influences UVP. PFMC instruction cues vary and often encourage anterior PFM recruitment that may result in sub‐maximal posterior facilitation. Study hypothesis: posterior or combined cues are more influential in optimizing UVP during PFMC following a brief practice period than anterior cue.

Methods

Seventeen pre‐menopausal, nulliparous, continent women were taught selective PFMC using different cues: anterior; posterior; anterior and posterior combined. Perineal ultrasound images of three PFMC for each cue were captured in supine and standing twice, 5 min apart. For reliability two raters measured data using angle of urethral inclination (AUI). Data analysis was undertaken using a customized General Linear Model ANOVA testing for interactions between all variables; subject, cue, posture, and test. Post hoc Bonferroni correction was used with a significance level of 0.05.

Results

The ANOVA showed significant differences between variables (P = 0.000). Post hoc analysis indicated significant differences between posterior and anterior cues 4.240° (P = 0.003); combined and anterior 3.756° (P = 0.009) but not between posterior and combined cues −0.484° (P = 1.00). Mean difference in AUI between supine and standing was 9.496° (P = 0.000); however, the interaction of cues and postures was not significant.

Conclusions

AUI was significantly more acute/optimal when PFMC instruction included a posterior cue. This may be due to optimal recruitment of puborectalis and other posterior regional muscles which may be sub‐maximally recruited with anterior cue. Investigation of the potential impact of these findings and possible usefulness of standardized instructions in PFM training is required. Neurourol. Urodynam. 30: 1620–1626, 2011. © 2011 Wiley Periodicals, Inc.
Graph labelings derived from models in distributed computing: A complete complexity classification
Authors: Chalopin Jérémie , Paulusma Daniël
Published: March 2011

We discuss 11 known basic models of distributed computing: four message‐passing models that differ by the (non)existence of port‐numbers and a hierarchy of seven local computations models. In each of these models, we study the computational complexity of the decision problems if the leader election and if the naming problem can be solved on a given network. It is already known that these two decision problems are solvable in polynomial time for two models and are co‐NP‐complete for another one. Here, we settle the computational complexity for both problems in the remaining eight models by showing that they are co‐NP‐complete. We do this by translating each problem into a graph labeling problem. By using this technique, we also obtain an alternative proof for the already known co‐NP‐completeness result. In the second part of our article, we completely classify the computational complexity of all the corresponding graph labeling problems, i.e., for every fixed integer
$k\geq 1$ we determine the complexity of the problem that asks whether a given graph allows a certain graph labeling that uses at most k labels. We also explain the close relationship of these labelings to graph homomorphisms that satisfy some further (global or local) constraints. This yields a new class of “constrained” graph homomorphisms that include the already known locally constrained graph homomorphisms. © 2011 Wiley Periodicals, Inc. NETWORKS, 2011