bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mass transport and mechanical properties of solid polymers
Authors: Doghieri Ferruccio , Sarti Giulio C. 
Published: March 2011

AbstractA general mathematical formulation is proposed for the description of the diffusion of low molecular weight species into a polymer matrix, in the presence of significant stress and deformation fields. The model is based on the usual momentum and mass balance equations; a crucial point is that it makes use of constitutive equations for the stress and for the diffusive mass flux which are not chosen independently of each other since they must obey precise thermodynamic restrictions; the latter are found in rather general terms.
Chemical transformations and phase transitions in polymer rheology and technology
Authors: Malkin A. Ya. , Kulichikhin S.G 
Published: March 2011

AbstractFundamental rheokinetic effects observed in processes of linear polymerization and three‐dimensional oligomer curing are discussed. It was shown that changes in rheological properties during linear polymerization can be described by relationships based on treating a reactive mass as a polymer solution, if a newly formed polymer is soluble in reactive medium. Phase separation limits this approach and leads to some new rheological consequences such as change in the rate of viscosity growth (in some cases viscosity can even decrease in the course of polymerization). Shearing influences temperature of a phase transition and kinetics of chemical reaction if it proceeds in heterogeneous conditions. The same phenomena were also observed for oligomer curing which can occur in heterogeneous manner with microgelation and formation of colloid particles of a new phase before the gelation of a system as a whole.
Phase behavior and structure in mesogen containing polyurethanes
Authors: Macknight W.J. , Papadimitrakopoulos F. 
Published: March 2011

AbstractThe mesophase to crystal phase transition observed upon heating the monotropic liquid crystal polyurethane (2,6‐LCPU‐6), based on the mesogenic biphenol 4,4′‐bis(6‐hydroxyhexoxy)biphenyl (BHHBP) and 2,6‐toluenediisocyanate (2,6‐TDI), has been investigated by differential scanning calorimetry (DSC), wide angle x‐ray scattering (WAXS) and infrared (IR) spectroscopy. Hexafluoroisopropanol (HFIP) fast solvent‐evaporation casting resulted in 2,6‐LCPU‐6 thin films with a glassy mesophase morphology. The mesophase to crystal exothermic transition has been observed by DSC between 130 and 140°C, depending on sample preparation. It is accompanied by a substantial increase of H‐bonding between urethane C=O and N‐H, as observed by IR. Curve fitting analysis of the conformationally sensitive amide I region revealed three bands; ordered H‐bonded carbonyl groups, disordered H‐bonded carbonyl groups, and “free” carbonyl groups. The prime feature of the 130°C transition is the substantial increase of ordered H‐bonded carbonyl groups at the expense of disordered H‐bonded carbonyl groups. Crystal melting occurs between 180 and 210°C and is accompanied by the complete disappearance of the ordered H‐bonded peak along with substantial changes in the frequency and width at half‐height of the disordered H‐bonded peak
Relaxation processes in oriented liquid crystalline polymers
Authors: Ward I.M. 
Published: March 2011

AbstractA review is presented of research on oriented thermotropic liquid crystalline polymers undertaken at Leeds University. A range of main‐chain polyesters has been studied based on 1,4‐hydroxybenzoic acid and 2,6‐hydroxynaphthoic acid as the primary monomers. By using a combination of dynamic mechanical, dielectric and NMR measurements insight has been gained into the molecular motions associated with the three principal relaxation processes. The behaviour in tension, for stresses parallel and perpendicular to the principal orientation direction, has been related to that in shear by use of mechanical models.
Fast switching ferroelectric liquid‐crystalline polymers
Authors: Scherowsky Günter 
Published: March 2011

AbstractThe principles of ferroelectricity, especially in liquid crystals (FLC) and polymers, are briefly presented. In a liquid‐crystalline side chain polyacrylate electro‐optical switching with response times of 200–400 μs was measured. Besides the ferroelectric switching an even shorter electroclinic switching process was detected.The influence of the spacer length and the molecular weight on the ferroelectric properties is discussed. The kind and number of chiral centers and their location in the side group strongly affects the electrooptical properties. In one polymer a change of the optical contrast caused by a sign reversal of the spontaneous polarization was found. In another FLC polymer three switching states (antiferroelectric behaviour) were detected. With coloured and fluorescent FLC polymers, obtained by mixing or by copolymerization new promising applications in electrooptical devices are expected.
Morphology control in polymeric multiphase systems with block copolymers and structured latexes
Authors: Riess Gérard 
Published: March 2011

AbstractSome application possibilities of block copolymers for the morphology control in polymeric multiphase systems are reviewed. The microdomain formation of block copolymers in the solid state is illustrated in the case of functionalized block copolymers and for interpolymer complexes. The preparation of “hairy latex” by emulsion polymerization in the presence of hydrophilic‐hydrophobic block copolymers is shown in connection with their applications in the controlled agglomeration process of latexes and for the preparation of polymer particles having microvoids. The surface activity of block copolymers in polymeric oil‐in‐oil systems is illustrated for silicone oil filled polymers. These materials have a low kinetic friction coefficient and act as reservoir systems with the lubricant incorporated in the polymer matrix.
Microscopic structures in phase inversion membranes: The use of polymer blends for membrane formation by immersion precipitation
Authors: Boom R.M. , Rolevink H.W.W. , Boomgaard Th. van den , Smolders C.A. 
Published: March 2011

AbstractMembrane formation by immersion precipitation has been investigated for two different polymer blends: poly(ether sulfone) / poly(vinyl pyrrolidone), a common blend for obtaining high performance UF or MF membranes, and poly(ether sulfone) / poly(styrene). The latter blend contains a polymer as additive that is not soluble in the precipitant used. It yields structures that confirm the fundamental basis of a model describing the formation of membranes from polymer blends. It appears that the membrane formation is dominated by the diffusional behaviour of the polymers relative to each other.A general classification of membrane structures from a polymer blend is presented; it is established that spinodal decomposition may well be responsible for the open porous structures usually found when using a polymer blend such as poly(ether sulfone) and poly(vinyl pyrrolidone).
Polymer membranes in medicine
Authors: Hugl Herbert , Dhein Rolf 
Published: March 2011

AbstractMass transfer within the human body primarily occurs across biological membranes. Medicine mimics nature and uses synthetic membranes for therapeutic purposes. The state of the art of polymer membrane applications in medicine is reviewed. The target for membrane material developments is mainly the improvement of the patients' safety and convenience. To provide optimal blood compatibility a new biocompatible polymer for hemodialysis membranes has been developed in our group: a polycarbonate with polyether blocks. The copolymer is suitable for production of membranes with excellent performance. In addition to therapeutic purposes polymer membranes can provide diagnostic functions. Recently a blood glucose test strip based on a synthetic membrane has been developed. The membrane separates off the erythrocytes and contains enzymes and reagents. It enables the diabetic a precise and convenient measurement.
Nonlinear optical properties of polymers and thin polymer films
Authors: S'Heeren G. , Derhaeg L. , Verbiest T. , Samyn C. , Persoons A. 
Published: March 2011

AbstractAn introduction to nonlinear optics (NLO) and the major challenges in the field of NLO‐properties of polymeric materials, is given in this paper. Methods for the investigation of nonlinear optical properties of [4‐(2‐methacryloxyethyl)methylamino]‐4′‐cyanoazobenzene copolymers with methyl methacrylate (MMA) are demonstrated: Electric Field Induced Second Harmonic Generation (EFISHG), Hyper Rayleigh Scattering (HRS), Second Harmonic Generation (SHG) in floating monolayers and SHG in poled polymer films. An example of phase‐transition analysis by SHG is given.
Monte Carlo simulation of polymeric materials: Recent progress
Authors: Binder K. 
Published: March 2011

AbstractMonte Carlo simulations are presented, dealing with phase diagrams of block copolymer melts and polymer blends, including the unmixing kinetics of the latter systems. The theoretical background is briefly reviewed: Ginzburg‐type criteria reveal that in mixtures of long flexible polymers a “crossover” occurs from mean‐field behavior (as described by Flory‐Huggins theory) to nonclassical Ising‐type behavior, and spinodal curves can be unusually sharp. This crossover is demonstrated by large scale simulations of the bond fluctuation model, and it is also shown that for symmetric mixtures the critical temperature scales with chain length as Tc α N. The prefactor in this relation is distinctly smaller than predicted by Flory‐Huggins, but the Curro‐Schweizer integral equation theory prediction Tc α √N is clearly ruled out. Tests of the Cahn theory on the initial stages of spinodal decomposition of polymer blends will also be reported.To conclude, the mesophase formation in block copolymers is discussed, and it is shown that the simulations agree very well with experiment. The pronounced chain stretching that already occurs in the disordered phase is compelling evidence against the validity of simple random phase approximation concepts for these systems. This shows how Monte Carlo simulations can assist in better understanding large classes of polymeric materials.
Modelling of solid polymers in chemical detail ‐ gases in amorphous polymers
Authors: Gusev Andrei A. , Suter Ulrich W. 
Published: March 2011

AbstractThe diffusion of gases in dense polymers, above and below the glass‐transition temperature, is described with a new Transition State Theory model that is based on the concept that the dynamics of small molecules dissolved in dense polymers is separated from the structural relaxation of the dense polymers. The model is used to study the dynamics of rare gases dissolved in atomistic micro‐structures of four polymers at 300 K: poly(dimethylsiloxane), poly(isobutylene), atactic poly(vinylchloride) and the polycarbonate of 4,4′‐isopropylidenediphenol (bisphenol‐A). Short‐time‐scale MD runs (5 ps) are used to characterize the elastic thermal motion of the host matrix; this information on mobility is then used for a stochastic simulation of solute dynamics up to ca. 1ms. All dissolved molecules show similar behavior by displaying three time regimes: a short‐time, high‐mobility domain, an intermediate time domain of anomalous diffusion, and a diffusive regime at long times. From the long‐time data diffusion coefficients are estimated; comparison with experimental data results in good agreement.
Molecular mechanics and the polymerization mechanism of homogeneous and heterogeneous Ziegler‐Natta catalysts
Authors: Guerra Gaetano , Cavallo Luigi , Venditto Vincenzo , Vacatello Michele , Corradini Paolo 
Published: March 2011

AbstractExamples of the application of simple molecular mechanics techniques to the study of the polymerization mechanism of various types of Ziegler‐Natta catalysts are reported. Details are given on the new mechanism of enantioselectivity suggested by molecular mechanics studies. The validity of the latter, involving a “chiral orientation of the growing chain” which had never been suspected before, has been experimentally proved both for homogeneous and heterogeneous catalysis.
Broad line NMR study of molecular motion in uniaxially stretched polymers
Authors: Egorov E. A. , Zhizhenkov V. V. , Zakrevskii V. A. , Ioffe A. F. 
Published: March 2011

AbstractCapability of NMR technique to study fracture and elementary destruction acts in polymers is discussed. Tensile stress influences macromolecular mobility As a rule mobility of macromolecules decreases under deformation. So far deformation remains reversible, this effect is reversible, too. As a result of chain micro‐Brownian motion hindering under stress the amorphous layers can pass from high‐elastic to solid state even at temperatures rather higher than Tg measured under initial conditions. It is mechanical vitrification (not structure changes) that is regarded as the general causes of draw process interruption (destruction of polymer).Deformation‐induced electron emission was detected. It is caused by ionization of stressed chains and tunnel transitions of electrons into deep traps. Influence of molecular mobility on the traps and their destroying under stress are considered.
Relaxation spectroscopy of LC main chain polymers: Experimental and theoretical investigations
Authors: Borisova Tamara , Fridrikh Sergey , Gotlib Yuli , Medvedev Grigoriy , Nikonorova Natalja , Skorokhodov Sergey , Zuev Vjacheslav 
Published: March 2011

AbstractA series of thermotropic main chain polymers with extended dimethylsiloxane segments was investigated. The study of dielectric properties of polymers revealed the relationship between their ability to form a mesophase and their molecular mobility. The peculiar behaviour of dielectric α‐relaxation parameters during the transition from mesomorphic to isotropic members of this polymeric series was shown. The theoretical approaches were developed for understanding macrochain dynamics of liquid crystalline polymers. The theoretical and experimental results are in good agreement.
Structure, dynamics and interactions in polymer systems as studied by NMR spectroscopy
Authors: Spĕvác̆ek Jir̆í , Straka Jaroslav 
Published: March 2011

AbstractThe possibilities of NMR spectroscopy in studies of interactions in polymer systems are demonstrated on the example of two types of macromolecular complexes: (i) By measuring 1H NMR high resolution line intensities, the formation of ordered associated structures of syndiotactic (s) poly(methyl methacrylate)(PMMA) in mixed solvents was quantitatively characterized. The obtained results permit us to assume that the mechanism by which the solvent affects self‐association of s‐PMMA involves specific interactions of the solvent molecules with PMMA units. Solid state high resolution 13C NMR spectra of associated s‐PMMA gels were also measured and compared with the spectra of a solid s‐PMMA sample. (ii) By using 13C solid state NMR spectroscopy, the differences in the structure of the amorphous and crystalline phases in pure poly(ethylene oxide) and its complexes with p‐dichlorobenzene or p‐nitrophenol were characterized. Prounounced differences also in the dynamic structure of the crystalline phase in these systems are indicated by the relaxation times T1(C), T1ρ(C) and T1ρ(H).
Stereoregular polymerization of β‐butyrolactone by aluminoxane catalysts
Authors: Pajerski Anthony D. , Lenz Robert W. 
Published: March 2011

AbstractA study was conducted on the application of aluminoxane catalysts to the polymerization of β‐butyrolactone, including the effects of polymerization solvent, temperature, type of aluminoxane, aluminoxane preparation, aluminoxane concentration, and modifications of the aluminoxane on the yield and tacticity of the polymer obtained. Optimal conditions for the synthesis of high molecular weight, highly isotactic poly‐β‐butyrolactone, PBL, were determined. Quantitative yields of crude PBL could be obtained, but removal of aluminum residues from the crude PBL by treatment with acetylactone resulted in large polymer losses. The polymer lost had a low molecular weight and an atactic stereochemistry. The purified PBL was of high molecular weight and high isotacticity.
Ring‐opening oligomerization reactions using aluminium complexes of schiff's bases as initiators
Authors: Le Borgne Alain , Vincens Valérie , Jouglard Muriel , Spassky Nicolas 
Published: March 2011

AbstractBifunctional telechelics with defined structure can be prepared by oligomerization of oxiranes, β‐butyrolactone and L‐lactide using aluminium Schiff's base complexes as initiators. Chiral initiator (SALCENAlCl) shows a stereoelective character leading to preferential oligomerization of one enantiomer from a racemic monomer mixture. The reaction with β‐butyrolactone proceeds through O‐alkyl cleavage. Alkoxy Schiff's bases aluminium complexes are used for oligomerization of L‐lactide. All the prepared oligomers were fully characterized by IR, elemental analysis, 1H and 13C NMR and GPC.
Polylactones 27. Anionic polymerization of L‐lactide. Variation of endgroups and synthesis of block copolymers with poly(ethylene oxide)
Authors: Kricheldorf Hans R. , Boettcher Caroline 
Published: March 2011

AbstractL‐Lactide was polymerized in toluene with various alkoxide initiators. These initiators were prepared in situ from potassium t.‐butoxide and primary or secondary alcohols such as tetradecanol, diethylene glycol butyl ether, menthol or testosteron. All these alcohols were incorporated as ester endgroups into the polylactide chain. However 1H‐NMR spectroscopy proves the existence of more OH‐endgroup than ester endgroups. This finding and 10–20% racemization observed for all anionic polymerizations suggest that chain‐transfer reactions with the monomer via deprotonation take place. When poly(ethylene glycol) monomethyl ether in combination with KOtBu was used as initiator, twoblock copolymers were obtained. With poly(ethylene glycol) A‐B‐A‐triblock copolymers could be synthesized. The quantitative reaction of the poly(ethylene glycol)s with L‐lactide could be proven by both 1H NMR spectroscopy and gelpermeation chromatography. DSC‐measurements show that depending on their lengths either the polylactide or the poly(ethylene oxide)blocks can crystallize. Due to partial racemization the melting temperatures (Tm) of the poly(L‐lactide) blocks did not exceed 155°C.
Branched polymers by cationic ring‐opening polymerization
Authors: Goethals E.J. , Trossaert G.G. , Hartmann P.J. , Engelen K. 
Published: March 2011

AbstractTwo methods for the synthesis of branched (co)polymers by cationic ring‐opening polymerization are presented. The first method is based on the spontaneous intermolecular termination that is observed in the polymerization of the four‐membered cyclic sulfides (thietanes). The branching points in these polymers are sulfonium ions. This method has been extended to polyether ‐ polysulfide block copolymers obtained by sequential polymerization of THF and a thietane. In the thus obtained AB block polymers, the branching points are concentrated in the sulfide segments only. By similar techniques, ABA types of block copolymer networks have been obtained making use of bifunctional initiators.The second method consists of copolymerizing a cyclic acetal such as 1,3‐dioxolane (DXL), with a “monofer”, which is a monomer that contains also a chain‐transfer function. As monofers for the DXL polymerization glycidol and glycerol formal were used. The end products are polyacetal‐polyols which contain a hydroxyl group at each of the chain ends. Reaction of these polyols with di‐isocyanates leads to the corresponding polyacetal polyurethanes.
Ring‐opening‐closing alternating copolymerization via zwitterion intermediates
Authors: Kobayashi Shiro , Lundmark Stefan , Kadokawa Jun‐Ichi , Uyama Hiroshi , Shoda Shin‐Ichiro 
Published: March 2011

AbstractThe present paper describes comprehensive results based on a new concept, i.e., ring‐opening‐closing alternating copolymerization. The copolymerization is given by combinations of ring‐opening of a cyclic monomer (A) and ring‐closing of a non‐cyclic monomer (B). The cyclic monomers used are five‐, six‐, and seven‐membered cyclic phosphonites and 2‐methyl‐2‐oxazoline. As a monomer (B), muconic acid, dialdehydes, di(meth)acrylic anhydrides, and N‐methyldiacrylamide are used. A 1:1 mixture of these monomers produced an alternating copolymer having a ring‐opened and a ring‐closed structural unit. A mechanism involving zwitterion intermediates is considered in all copolymerizations.
Mechanism of formation of cyclic species in cationic ring‐opening polymerization of cyclodimethylsiloxanes
Authors: Sigwalt P. , Masure M. , Moreau M. , Bischoff R. 
Published: March 2011

AbstractA general feature of the cationic polymerization of all cyclodimethylsiloxanes is the formation of various cyclic products (cyclics) together with that of a linear high polymer. However, the types of cyclics as well as their rate of formation may vary considerably according to the number x of D units ((CH3)2SiO units) in the monomer. The case of initiation by trifluoromethanesulfonic (triflic) acid in methylene chloride solution at 20°C has been particularly studied.With D4, D5, D6 and D7, for which the polymerization rate increases with the size of the ring, all types of cycles Dx are formed in relative amount decreasing with their size ([D7] < [D6] < [D5] < [D4]). The high polymer final concentration and molecular weight are independent from triflic acid concentration. This may result from a polymerization‐depolymerization reaction, involving all the cyclics formed by back‐biting reactions occurring with silyl triflates activated by the acid, and leading finally to an equilibrium.The situation with D3 is completely different. The high polymer (HP) and the cyclics (D3x multiples of D3 like D6, D9, …) are formed simultaneously under kinetic control. The yields of the various cyclics (formed in amount often larger than that of the HP) are proportional to that of the linear HP. The latter is formed from the beginning of the reaction with a molecular weight proportional to HP yield and inversely proportional to the acid concentration.The opposite role of added water on the polymerization is discussed: an activating effect for D3, and a desactivating one for D4, D5 and D6. “Copolymerization” experiments between D3 (or D4) and tetramethyldisiloxane diol confirmed the effect of water and gave new informations about the occurrence ‐ or absence ‐ of condensation reactions in the mechanism of the growth of the polymer chains.A discussion leads to the conclusion that while the cationic polymerization of D4 by triflic acid is propagated by activated triflic esters, that of D3 may also involve the monomer activated by the higher hydrates of the acid and linear oligomeric silanol esters. The latter, formed continuously, may also give the D3x cyclics by intramolecular heterocondensation.
Fire retardant polymers in the future: Safety by tests or engineering?
Authors: Woolley David 
Published: March 2011

AbstractThe selection and control of fire retardant polymers for most current applications is made by a prescriptive approach supported by standard tests. There is now much international interest and commitment to new fire safety strategies based on fire safety engineering. This paper outlines some of the issues which need to be addressed over the next decade, if the full benefits of fire retardant polymers are to be recognised in total fire safety designs.
The relationship between thermal degradation and flammability
Authors: McNeill Ian C. 
Published: March 2011

AbstractThe relationship between flammability and thermal degradation is the consequence of the burning cycle needed to sustain fire. Thermal degradation behaviour of polymers is discussed in relation to generation of fuel and other products, including flame quenchers, and the production of char. The thermal degradation behaviour of the main classes of fire retardant is considered and illustrated by examples of the ways in which specific fire retardants exert their effect on a particular polymer.