bluuebunny/crossref_metadata_2025 huggingface dataset:
Polymer membranes in medicine
Authors: Hugl Herbert , Dhein Rolf
Published: March 2011

Mass 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

An 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

Monte 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

The 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

Examples 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

Capability 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

A 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

The 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

A 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

Bifunctional 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

L‐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

Two 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

The 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

A 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

The 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

The 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.
Some aspects of polymer pyrolysis
Authors: Zaikov G. E. , Aseeva R. M.
Published: March 2011

Pyrolysis is the important stage of polymer combustion. This process depends on molecular and submolecular structure of polymer as well as conditions of heat affect. It may be realized through the formation of nonvolatile carbonized product. The basic conception of the present work consists in the transformation of macromolecules into carbonized structure which realises by means of formation of the thermodynamically‐advantageous intermediate compounds with a system of π‐conjugated unsaturated carbon bonds (acyclic or aromatic nature) and by their following conversion into condensed aromatic structures.

It has been examined the correlation between the structure and properties of carbonized products and the flammability of polymers.
Flame retardant chemical mechanisms of flame retardant viscose fibres and blends with polyester
Authors: Nousiainen Pertti , Heidari Shahram
Published: March 2011

A systematic investigation of structurally identical flame retardant viscose, modal and polyester blended fabrics and fibres was carried out in order to develop a chemical basis for more effective products based on organic and inorganic flame retardants. The oxygen indices and chemical compositions of phosphorus‐nitrogen flame retardants (P‐N) were used in efficiency and synergy evaluations. A new flame retardant viscose fibre containing silicid acid was included in the comparative evaluation procedure. Thermal gravimetry and X‐ray diffractometry were used for determine physical factors during pyrolyzing of fibres. Charred residues were analyzed by applying elementary and solid 13‐C NMR (CPMAS) spectrometry. The pyrolysis gas‐liquid chromatographer connected with a gas phase FT infrared spectrometer was applied to identify the decomposition products of P‐N‐containing fabrics.
Mechanistic aspects of intumescent fire retardant systems
Authors: Camino G. , Costa L. , Luda M. P.
Published: March 2011

The mechanism of intumescence is studied in mixtures of ammonium polyphosphate (APP) with several polycondensates as a part of a systematic study of intumescent fire retardants. It is shown that APP reacts on heating with the polycondensate to form a precursor of the intumescent char which is obtained on further heating. The introduction of the intumescent system in polypropylene does not modify the structure of the char formed on heating. However, the polymer modifies the foaming behaviour of the system. The thermal decomposition of the char occurs with volatilisation of phosphorus moieties and formation of a relatively thermally stable residue. Effects of the thermal behaviour of the char, on fire retardance, are discussed.
Thermoanalytical studies of intumescent systems
Authors: P. Taylor Andrew , R. Sale Frank
Published: March 2011

Fire retardant intumescent coatings which produce a swollen char on heating are being frequently used to protect buildings containing structural steel from the effects of exposure to high temperatures caused by fire. This paper contains details of a study carried out using thermal analysis techniques to elucidate the mechanisms of the development of intumescent chars during the heating of an intumescent coating system based on ammonium polyphosphate, pentaerythritol and melamine. In particular, the role of melamine as the spumific agent has been studied. The melamine is shown to react chemically with the ammonium polyphosphate in addition to carrying out its role as the spumific, or blowing agent.
The use of thermographic technique in the evaluation of polymers combustion and fire retardants performance
Authors: Bertelli G. , Benassi R. , Marchini R. , Camino G. , Costa L. , Luda M. P.
Published: March 2011

The combustion behaviour of polymeric materials either fire retarded or not, burning in the Glow Wire and UL 94 tests, was characterised by means of thermography. It is shown that the distribution of temperatures in the gas and condensed phase of the burning specimen thus recorded, supplies fundamental complementary information for the characterisation of the combustion process.
The chemistry of smoke suppression in polyurethane foams using thermogravimetry‐infrared residue analysis
Authors: Anthony Geoffrey M.
Published: March 2011

The analysis of TG residues using FT‐IR has shown that at 270°C. pyromellitate esters can react with aromatic amines formed from polyurethane foam degradation to form a pyromellitimide structure. This stabilises the main smoke and toxic gas precursors formed during combustion.
Practical aspects of modeling ignition and burning of organic polymers 1. The case of PE loaded with mixtures of Al (OH)3 and Hg(OH)2 or MgCO3
Authors: Rychlý Jozef , Búcsi Alexander , Csomorová Katar ína , Rychlá Lyda , Šimúnková Dagmar
Published: March 2011

A correlation has been found between limiting oxygen index and tendency towards decomposition into volatiles as determined from nonisothermal thermogravimetry for polyethylene charged with the mixtures of Al(OH)3 and Mg(OH)2 or MgCO3. An interpretation based on the model of ignition and burning of polymers has been put forward and a dependence of heat transfer coefficient on temperature of ignition and initial mass of sample was found.
Fire retardants and fire safety how can tests reflect reality?
Authors: Becker Wolfram
Published: March 2011

In the standard test methods, the thermal action proceeds even today in most cases under the conditions of the well ventilated fire. The intensity of the thermal action varies widely, however, depending on the designed safety level. In the last few years, the outstanding purpose was to test the behaviour of products under the action of fire, in particular the time to the flash‐over. The intensity of the fire action rises accordingly, despite the possibility of further free ventilation, to such a degree that the test conditions in laboratory processes can reflect reality only under certain conditions.

This philosophy is drawn from the results of statistical investigations in the U.S. is that the time to the flash‐over in a room is equal to the time to untenability, because most of the victims of the fire were not present in the room where the fire broke out. Test methods on a real scale that serve this designed safety level will therefore have to work with the high fire action on the products to be tested.

In contrast, however, in some European countries the philosophy underlying the adoption of designed safety levels is that the main purpose is to protect human beings who are present in the room where the fire breaks out. According to this philosophy, a fire development that threatens to become dangerous must always be prevented. Consequently, interest is focused mainly on restricting the spread of fire and thus preventing a flash‐over. The test methods to be designed with this purpose in view should, therefore, simulate the conditions of the starting fire or the developing fire. The efficiency of a fire retardant can then be evaluated according to whether the fire spread is restricted or not. Under these conditions, the question of the time to be flash‐over is of no significance.

With standard tests, it is impossible to make a statement as to how far the fire safety of products can be improved by the use of fire retardants unless the safety‐relevant range of application for the test method has been defined.
Thermal and flammability behaviour of copolymers of N‐(2, 4, 6‐tribromophenyl)maleimide with some acrylates
Authors: Janović Zvonimir , Malavašić Tatjana , Sarić Karla
Published: March 2011

The copolymers of N‐(2, 4, 6‐tribromophenyl)maleimide (TBPMI) with methyl acrylate, methyl methacrylate and acrylonitrile of different composition were prepared by free radical polymerization at low conversion. Their thermal behaviour was established by TGA measurements in helium atmosphere and flammability properties were determined by limiting oxygen index method. The higher TBPMI content in the copolymer led to a higher thermal stability and lower flammability particularly when Sb2O3 was used as a synergist.
The use of fluorinated additives in fire retardance of polymers
Authors: Roma P. , Luda M. P. , Camino G.
Published: March 2011

Polytetrafluoroethylene (PTFE) is shown to improve fire retardance characteristics of brominated compounds/antimony trioxide systems added to polymers burning with or without dripping, as for example high‐impact polystyrene or acrylonitrilebutadiene‐styrene terpolymer, respectively. The action of PTFE seems to be the reduction of intrinsic flammability of the material as shown by parallel improvement of Underwriters Laboratories (UL94) tests and oxygen index parameters. A mechanistic interpretation is tentatively proposed which takes into account the very high effectiveness of PTFE.
Mechanisms of fire retardance in glass fibre polymer composites
Authors: Casu A. , Camino G. , Luda M. P. , De Giorgi M.
Published: March 2011

It is shown that the introduction of glass fibres in the poly(butylene terephthalate) (PBT) matrix, increases its flammability. The mechanism of action of a typical fire retardant for PBT which is a mixture of a brominated organic compound and antimony trioxide, seems to involve both the condensed and the gas phase.
Opportunities and threats in polymer based materials science and technology
Authors: Clark David T.
Published: March 2011

Despite the fact that materials research has completed an innovative and exciting decade from a fundamental science perspective, the fact remains that at the exploitation stage commercial returns on the R&T Investment made by large companies has been poor. In this article we look at one such company's experience; at the general challenge of maintaining a strategic research capability in the face of drastic business reorganisation and address some of the interesting challenges and threats for the polymer community (in academe and industry) over the next decade.
Surface phenomena at polymers
Authors: Jacobasch Hans‐Jörg
Published: March 2011

Polymers with advanced properties can be achieved among other measures by reinforcing with fibrous materials, by polymer blending and surface modification. Using the surface treatment of PP‐EPDM injection moulding specimens (washing, flaming, plasma‐treatment) an overview on progress in surface analytics is given. It is shown that XPS, contact angle and zeta‐potential measurements give corresponding results concerning the composition of the surface region.

Additional to the kind of interaction forces at interfaces the mechanical properties of reinforced polymers are governed by sorption layers and electrical phenomena at interfaces. Corresponding results were obtained at chalk filled PE‐HD and glass fibre reinforced polyamide.
Specialty and advanced polymers by carbocationic macromolecular engineering
Authors: Iván Béla
Published: March 2011

This study briefly surveys a variety of new advanced polymeric materials and controlled synthetic processes available by carbocationic macromolecular engineering techniques and having potential commercial interest. These recent developments, mainly by living carbocationic polymerization, have led to new opportunities in polymerization process control, and in designing microstructure, functionality, molecular weight and molecular weight distribution (MWD) and thus properties of a wide variety of unique polymer systems. The fundamentals of these new emerging technologies and the novel materials offered by them, such as macromonomers, telechelics, polymers with pendant functional groups (liquid crystalline homo‐ and co‐polymers, non‐linear optical materials etc.), star‐shaped macromolecules, block and graft copolymers, high temperature polymers, and specialty networks (amphiphilic networks and rubber toughened bone cements) as potential biomaterials will be overviewed.
Synthesis of copolyesters via interchange reactions with polypivalolactone
Authors: Tijsma Edze Jan , van Der Does Leen , Bantjes Adriaan , Vulić Ivan , Buning Gerard Hidde Werumeus
Published: March 2011

The synthesis of copolyesters via interchange reactions of polypivalolactone (PPVL) with bisphenol‐A polycarbonate (PC) and dimethyl terephthalate (DMT) was studied. Random copolyesters with high thermal stability were obtained by heating PPVL with PC and DMT in the melt at 280 °C in the presence of tetrabutylorthotitanate (TnBT) as a catalyst. Results from SEC measurements showed that the values for Mn of these copolyesters ranged from 7,000 to 16,000. The process for preparing these copolyesters was studied in detail and based on the results of these studies, the reactions occurring during copolyester synthesis were discussed. It was found that in the early stages of the process mainly interchange reactions occurred between PPVL and PC chains, whereas the amount of terephthalate units increased only after longer reaction times.
Reactive blending of polypivalolactone with polycarbonate
Authors: Tijsma Edze Jan , van Der Does Leen , Bantjes Adriaan , Vulić Ivan , Buning Gerard Hidde Werumeus
Published: March 2011

Blends of polypivalolactone (PPVL) with bisphenol‐A polycarbonate (PC) were studied. Physical PPVL/PC blends showed one Tg close to the Tg of 145 °C for PC, indicating immiscibility. Reactive blending of PPVL and PC with 0.5 wt.‐% tetrabutylorthotitanate was performed in diphenyl ether (260 °C) and in a twin screw extruder (TSE) at 280 °C. Based on the results from NMR, FT‐IR and thermal analysis, it was concluded that interchange reactions had occurred. The thermal properties indicated that, due to these interchange reactions, PPVL/PC blends had become more miscible. Although blending in a TSE was more efficient with respect to interchange reactions compared with blending in diphenyl ether, complete randomization was not observed.
Polyacrylamide–graft–poly(ethylene oxide)
Authors: De Vos S. C. , Möller M.
Published: March 2011

Water‐soluble graft copolymers were synthesized by copolymerization of acrylamide with mono‐methoxy‐poly(ethylene oxide)‐methacrylates (Me‐PEO‐MA). The Me‐PEO‐MA macromers were synthesized by a catalytic esterification of methacrylic acid with mono‐methoxy‐poly(ethylene glycol)s with different molecular weights. The graft copolymers obtained were characterized by 1H‐NMR spectroscopy, gel permeation chromatography (GPC) and Ubbelohde viscosimetry. The rheological behaviour of aqueous polymer solutions, which are expected to show hydrophobic association at elevated temperatures, was studied with a cone and plate‐rheometer.
A program generator for describing copolymerization and network formation in step reactions
Authors: Tiemersma‐Thoone G.P.J.M. , Scholtens B. J. R. , Braam A. W. M.
Published: March 2011

A multi‐purpose computer program has been developed for describing copolymerization and network formation in step reactions. It operates at two hierarchical levels: a generation level and an application level. At the generation level, the class of problems is defined and prepared, and this information is used to generate automatically a problem‐specific program based on generalized concepts of the branching theory. At the application level, the problem‐specific program can be used for model calculations with all possible variations in recipes and kinetic parameters within the boundaries of the specific class of processes concerned.
Mechanical and stress‐optical properties of strongly swollen hydrogels
Authors: Schröder U. P. , Oppermann W.
Published: March 2011

Crosslinked polyelectrolytes exhibit extreme swelling in aqueous systems; fluid uptake usually amounts to 100 to 1000 times of their dry volume. The mechanical and stress‐optical properties of such highly swollen gels show some peculiarities because the network chains are stretched far beyond the Gaussian limit. The shear modulus increases markedly at high degrees of swelling, and the stress‐optical coefficient decreases.

A quantitative treatment has to be based on non‐Gaussian chain statistics. In order to provide experimental data, stress‐optical and modulus measurements were carried out on hydrogels made from partially hydrolyzed poly‐(acrylamide) and other polyelectrolytes. The degree of swelling was adjusted by using aqueous NaCl‐solutions of different concentration as the swelling medium. Using a description based on the inverse Langevin function, the course of the shear modulus on the degree of swelling can be fitted to the experimental data. The optical modulus, n/(λ2‐λ−1), is predicted with somewhat less agreement. However, a different set of parameters has to be used for the mechanical and optical properties. This shows that the treatment is not fully consistent.
The viscoelastic behaviour of elastin in aqueous ethylene glycol
Authors: Lillie M. A. , Gosline J. M.
Published: March 2011

The viscoelastic behaviour of arterial elastin in aqueous ethylene glycol has been studied to compare the effects of two solvents of differing polarity. The behaviour of elastin in low concentrations of ethylene glycol was similar to that of elastin that had been indirectly dehydrated using polyethylene glycol as an osmotic agent. That is, at low concentrations the dominant effect of ethylene glycol was to reduce the activity of the water molecules. However, at high concentrations, ethylene glycol appeared to interact directly with the elastin, altering both the swelling and the viscoelastic behaviour of the network.
Circular dichroism of aqueous solutions and gels of partial benzyl esters of the polysaccharide gellan
Authors: Crescenzi Vittorio , Dentini Mariella , Maschio Sergio , Segatori Maurizio
Published: March 2011

Three partial benzyl esters of gellan have been studied by means of circular dichroism spectroscopy in aqueous tetramethylammonium chloride solution and in the gel state (aqueous NaCl). Thermal stability of the solution ordered chain states as well as of the gels, maximal in the case of gellan, markedly decreases with increasing degree of esterification.
Contribution of entanglements to the modulus of end‐linked poly(ethylene oxide) networks
Authors: Larsson Iben , Kramer Ole
Published: March 2011

Poly(ethylene oxide) networks were made at 75 °C by end‐linking of short linear chains with an excess of Tolonate HDT, a tri‐functional aliphatic isocyanate. Molecular weights of poly(ethylene oxide)were 4000, 6000 and 12000. The observed elastic moduli were much higher than predicted from affine theory, indicating a large contribution from entanglements in contrast to the findings of previous studies. With increasing excess of cross‐linker, the contribution from entanglements levels off at a value of approximately 5 MPa which is in good agreement with the rubber plateau modulus of pure poly(ethylene oxide).
Studies on the solution behaviour of self‐assembling polymeric systems
Authors: Stock Jochen , Stadler Reimund
Published: March 2011

Functional groups were attached to styrene‐butadiene copolymers with different polymeric architectures and a low molecular weight compound. These polar stickers form binary, chelate‐like contacts or extended juntion zones depending on their chemical nature. The solution properties of these amphiphilic species in toluene were studied by static light scattering.
Structure of filled rubbers and mechanism of reinforcement
Authors: Strauß Michael , Pieper Thomas , Peng Weiguo , Kilian Hanns‐Georg
Published: March 2011

It will be shown that a consequent modelling of filler‐to‐filler and filler‐to‐matrix contacts and of individual slippage processes allows to describe the mechanical deformation behaviour of rubbers filled with rigid filler particles. The phenomenon of reinforcement turns out to be due to non‐Gaussian rubber elasticity (van der Waals network). Surprisingly, there are universal aspects which characterize the fractal structure in the composite as well as the processes under large strain. Moreover it is possible to deduce the atomic distance distribution in the adhesional layers from WAXS‐measurements. Together with a description of the WAXS‐pattern of pure graphitized and degraphitized carbon blacks some new aspects of the conditions to maximize the filler‐to‐matrix adhesion will be discussed.
Dielectric cure characterization of model elastomers
Authors: Xu Xiaofeng , Galiatsatos Vassilios
Published: March 2011

Isothermal dielectric properties of poly(dimethylsiloxane) (PDMS) networks during cure were studied at room temperature with emphasis on the effect of catalyst concentration. The frequency range employed was 10−1 to 105 Hz. The dielectric response is sensitive to a change in catalyst levels as this was evidenced by the change in the values of the logarithm of the loss factor log ϵ”. We attribute these changes to dipolar and ionic contributions. A profile of the cure reaction of model elastomers may readily be obtained by using a combination of microsensors and time‐domain dielectric spectroscopy. The results obtained show that the catalyst concentration affects both crosslinking and chain extension reactions. However, for the typical catalyst concentration at which typical networks are prepared, the crosslinking reaction is the dominant effect.
Quasi‐elastic neutron scattering in gels and solutions
Authors: Geissler Erik , Hecht Anne‐Marie , Guillermo Armel , Horkay Ferenc , Legrand Jean François , Mallam Simon
Published: March 2011

Measurements of swelling pressure, neutron spin‐echo scattering, and dynamic light scattering were made in an end‐linked poly(dimethylsiloxane) (PDMS) gel swollen to equilibrium in a good solvent (toluene) and also in the equivalent solution. The macroscopic osmotic modulus is depressed in the gel. Neutron spin echo observations at intermediate and high values of the scattering vector Q reveal that the mobility of the monomers is unaffected by cross‐linking. Elastic neutron scattering at small Q detects non‐uniformities in the polymer concentration distribution, which are absent from the solution. These non‐uniformities play a major role in the dynamic response of the system at lower Q, and and appear to be the cause of the observed reduction in osmotic pressure.
Chemical pattern formation in gels
Authors: Kárpáti‐Smidróczki éva , Büki András , Zrínyi Miklós
Published: March 2011

Precipitate forming chemical reactions have been studied in chemically crosslinked poly(vinyl alcohol) gel medium. One of the reactive components was incorporated into the gel, the other was allowed to diffuse into the swollen network. This reaction‐diffusion process often results in pattern formation which can occur intermittently in terms of time and space or both. Experiments were carried out in order to investigate the effect of various factors (crosslinking density, swelling degree as well as the concentrations of the outer and inner electrolyte). The following precipitates were intensively studied: Mg(OH)2, Cr(OH)3, PbCl2. Three basically different morphologies (Liesegang band formation, moving bands and tree‐like structure) have been observed and investigated. One‐ and twodimensional computer simulations were carried out in order to establish the influence of various factors on the precipitation.
Stress‐optical properties of bimodal polymer networks
Authors: Subramanian P. R. , Galiatsatos V.
Published: March 2011

The optical properties of bimodal poly(dimethylsiloxane) (PDMS) networks were studied with special emphasis on the non‐linear stress optical properties exhibited by these materials. In particular the effect of chain length, and junction functionality on the strain induced birefringence was investigated. It is shown that for the non‐linear properties to clearly manifest themselves a critical concentration of short chains is essential and that the junctions are tetra‐functional. However, all bimodal compositions studied were found to exhibit a non‐linear variation of birefringence with strain irrespective of the junction functionality. The optical properties of the unimodal networks were found to vary linearly with stress and strain as expected. The transition from non‐linear to linear optical behavior on increasing the molecular weight of the short chains is also established.
A rheological study of latex polystyrene‐based model systems
Authors: Nemirovski Naum , Narkis Moshe
Published: March 2011

Latex two‐phased polystyrene blends have been produced by three different mixing routes. Polystyrene (PS) and lightly crosslinked polystyrene (XPS) latices were either mixed, or else used as seeds in two‐stage polymerizations. This resulted in different microstructures by each of the procedures, leading to different rheological behaviors. Latex PS/XPS systems flow at every composition studied. Activation energies are independent of XPS content, and of the same order of magnitude as PS. Power‐law relaxation has been observed for the physically blended system in the terminal region. This has been attributed to the formation of a “continuous” XPS network in the range 60–100% XPS.
The elasticity of nematic networks
Authors: Bladon P. , Warner M.
Published: March 2011

Nematic rubbers are composed of crosslinked polymer chains with stiff rods either incorporated into their backbones or pendant as side chains. When nematic effects axe strong, such rubbers exhibit discontinuous stress‐strain relationships and spontaneous shape changes. We model such a rubber using Gaussian elasticity theory, including the nematic interaction via a mean field. Results are presented for the cases of uniaxial extension and compression. Under uniaxial extension the rubber can undergo a first order phase transition to a uniaxial nematic phase. Under uniaxial compression first or second order transitions are possible to genuinely biaxial nematic states with biaxial strains. When nematic effects are very small (i.e. T >> Tc where Tc is the nematic‐isotropic phase transition temperature of the rubber) we postulate that the model is a good approximation to a conventional, non‐nematic elastomer, and fit our model to data from an isoprene rubber.
Dendritic analogues of engineering plastics ‐ a general one‐step synthesis of dendritic polyaryl ethers
Authors: Miller Timothy M. , Neenan Thomas X. , Kwock Elizabeth W. , Stein Susan M.
Published: March 2011

The first general single‐step route to dendritic or cascade polyaryl ethers analogous to common linear polyaryl ethers is described. The sodium salts of four AB2 monomers each containing a single phenolic hydroxyl group and two aryl fluorides activated toward nucleophilic substitution by carbonyl, sulphonyl, or tetrafluorophenyl moieties are shown to polymerize in hot N, N‐dimethylacetamide. The products are high molecular weight polymers (7000 < Mn < 36000), have narrow polydispersities (1.50 < Mw/Mn < 4.50), and are highly soluble in organic solvents. The molecular weights of two of the polymers increase with monomer concentration. The polymers are thermally stable (500 °C under N2) and have glass transition temperatures ranging from 135 to 231 °C.
Structural rigidity control in arborescent graft polymers
Authors: Gauthier Mario , Möller Martin , Burchard Walther
Published: March 2011

Successive chloromethylation‐anionic grafting sequences on polystyrene have led to well‐defined hyperbranched macromolecules. Polymers with branching functionalities f > 5000 and molar masses over 107 g/mol were thus prepared while maintaining a ratio of mass‐ to number‐average molar masses Mw/Mn = 1,1‐1,3. Three series of styrene polymers were prepared by varying the density of grafting sites along the chain, resulting in controllable stiffening of the molecular structure. Characterization of the branched molecules by size‐exclusion chromatography/low‐angle laser light scattering and light scattering confirmed a geometric increase in molar mass for successive generations, and a low ratio of mass‐ to number‐average molar masses. Static and dynamic light scattering experiments showed that the molecules behave like hard spheres in dilute solutions. Measurements in the semidilute range, however, showed a progressive structural stiffening effect as the branching density increases.
Large‐scale production of polypropylenimine dendrimers
Authors: De Brabander‐Van Den Berg E.M.M. , Nijenhuis A. , Mure M. , Keulen J. , Reintjens R. , Vandenbooren F. , Bosnian B. , De Raat R. , Frijns T. , v.D. Wal S. , Castelijns M. , Put J. , Meijer E. W.
Published: March 2011

The synthesis and characterization of a new series of polypropylenimine dendrimers is reported. Using a repetition of the sequence of a Michael addition to a primary amine, followed by a heterogeneously catalyzed hydrogenation, ultra‐pure polypropylenimine macromolecules with molecular weights up to 6912 are synthesized. The reaction sequence allows the preparation of these dendrimers at very large scales, whilst the availability of a simple purification in the sequence affords ultra‐pure samples. The polypropylenimine dendrimers are fully characterized; apart from the first 0.5 generation they are all oils, possess a Tg in the range from −90 to −40 °C, are unexpectedly stable, and their intrinsic viscosity drops after generation 4.
Towards the self‐assembly of polyrotaxanes
Authors: Sun Xiaoqiang , Amabilino David B. , Ashton Peter R. , Parsons Ian W. , Fraser Stoddart J. , Tolley Malcolm S.
Published: March 2011

The self‐assembly of a number of rotaxanes, pseudorotaxanes, and a pseudopolyrotaxane based on the π‐electron deficient cyclobis(paraquat‐p‐phenylene)d̊ and threads and dumbbell components composed of π‐electron rich hydroquinone rings incorporated symmetrically within polyether chains terminated in the case of the rotaxanes by adamantoyl stoppers.
Supramolecular self‐assembly based on directed hydrogen bonding
Authors: Fan Erkang , Yang Ji , Geib Steven J. , Vicent Cristina , Garcia‐Tellado Fernando , Tecilla Paolo , Hamilton Andrew D.
Published: March 2011

A series of hydrogen‐bonding monomers has been constructed and shown to form discrete aggregates both in solution and in the solid state.
Towards tobacco mosaic virus‐like self‐assembled supramolecular architectures
Authors: Percec V. , Heck J. , Johansson G. , Tomazos D. , Ungar G.
Published: March 2011

This paper discusses the molecular design of selected examples of structural units containing taper shaped exo‐receptors and various crown ether, oligooxyethylenic, and H‐bonding based endo‐receptors, which self‐assemble into cylindrical channel‐like architectures via principles resembling those of tobacco mosaic virus (TMV). The ability of these structural units to self‐ assemble via a delicate combination of exo‐and endo‐recognition processes will be presented. A comparison between various supramolecular (generated via H‐bonding, ionic, and electrostatic interactions) and molecular “polymer backbones” will be made. The present limitations concerning the ability to engineer the structural parameters of these supramolecular channel‐like architectures and some possible novel material functions derived from them will be briefly mentioned.