bluuebunny/crossref_metadata_2025 huggingface dataset:
Polymerization and molecular recognition in the monolayers of the surface‐active derivatives of crown‐ethers
Authors: Zaitsev Sergei Yu. , Vereschetin Vadim P. , Zubov Vitalj P.
Published: March 2011

The four surface‐active derivatives of crown‐ethers with a variety of fatty alkyl chains were synthesized and studied in monolayers at various conditions. The areas per crown‐ether molecule in monolayers are increasing significantly in the presence of various alkali metal cations in the aqueous subphase. These effects can be explained as complex formation between crown‐ethers in the monolayers and cations from aqueous subphase, causing a change in the conformation of the polyether ring of the molecule at the interface. This is accompanied with the change in the cation selectivity (Na+ > Li+ > K+ > Cs+) as compared with the series in volume (K+ > Cs+ > Na+ > Li+). Polymerization of the crown‐ether monolayer allows to stabilize the conformation of the molecule at the interface as if tuned to the definite cation.
Self‐assembly phenomena in multicomponent systems composed of polyelectrolytes and ionic surfactants
Authors: Zezin Alexander B. , Izumrudov Vladimir A. , Kabanov Victor A.
Published: March 2011

The ability of anionic surfactants to expel fluorescencetagged poly(methacrylate) polyanion (PMA*) from nonstoichiometric water‐soluble interpolyelectrolyte complex (NIPEC) formed by PMA* and polycation‐quencher poly(N‐alkyl‐4‐vinylpyridinium) (PAlkVP) and to form polyelectrolyte‐surfactant complex (PESC): NIPEC(PMA*‐PAlkVP)+surfactant ⇔ PESC(PAlkVP‐surfactant)+PMA* was revealed and studied by fluorescence quenching technique and high‐speed sedimentation. It was found that the transfer of poly(N‐ethyl‐4‐vinylpyridinium) from NIPEC to PESC proceeded up to complete conversion providing a self‐assembly of both PESC and NIPEC particles in the course of the reaction. The concentration of the surfactant and the “tail” length of the surfactant molecule, as well as the structure of Alk groups, temperature, pH, ionic strength, and the nature of added low‐molecular‐weight electrolyte proved to be the factors of the reaction equilibrium control.
Hierarchical structures in natural and synthetic polymer science
Authors: Baer Eric , Hiltner Anne
Published: March 2011

The founders of our dynamic field uncovered the wonders of both natural and synthetic polymers by using relatively primitive instruments and techniques. They developed the foundations on which we now build complex materials systems. By using the lessons from macromolecular systems in biology, our scientific community is now designing synthetic polymers that mimic natural materials (1, 2). This paper is divided into two parts.

1. Hierarchical structure‐property relationships in connective tissues‐lessons from biology

2. Micro‐ and nano‐ layered polymeric systems
Self‐assembling with formation of mesogenic polymer structures in non‐mesogenic species
Authors: Plate' N. A. , Talroze R. V.
Published: March 2011

The trivial statement that liquid crystals are formed on the base of either mesogenic organic molecules or molecules with amphiphilic structure may be applied to polymers as well. But at the same time it became clear that polymer LC world in certain sense is richer than the low‐molecular one and more and more one finds mesophase and LC polymers based on non‐mesogenic macromolecules. Linear polyphosphazenes, polysiloxanes, some ladder polymers etc. exhibit mesophase behavior in absence of any mesogenic groups in their structure.
Selectivity as a measure of “livingness” of the polymerization of cyclic esters
Authors: Penczek Stanislaw , Duda Andrzej
Published: March 2011

The selectivity parameter, defined as the ratio of the rate constant of desired elementary reaction (i.e. initiation or propagation) to the rate constant of the competing side reaction, should be used as a quantitative measure of the livingness of polymerization. The most important side reactions in the anionic and pseudoanionic polymerization of cyclic esters are presented and the importance of selectivity in initiation and propagation is discussed, taking into account the relation between selectivity and the structure of monomers, initiators, and active species. Reasons for the low selectivity of ions and the high selectivity of aluminium‐based initiators, namely dialkylaluminium alkoxides (R2AlOR') and aluminium trialkoxides (Al(OR)3) are given. The relatively low reactivity and steric hindrance, created by the presence of bulky substituents at the Al atom, are responsible for the enhanced selectivity. Thus, Al(OR)3 found recently to carry three chains, provides particularly crowded and therefore selective active species. The structure of the aluminium alkoxide active species is described, as established on the basis of 1H NMR, 27Al NMR, and molecular weight measurements by Multi Angle Laser Light Scattering (MALLS) of the living polymers.
Cationic polymerization with titanium(iv) compounds: Living polymerization and possibility of stereoregulation
Authors: Sawamoto Mitsuo , Kamigaito Masami
Published: March 2011

This paper deals with the development of living cationic polymerizations and the possibility of stereoregulation therein based on the modulation of the Lewis acid activators by their ligands. For this, titanium(IV) chlorides [TiCl4‐n(OR)n] with various alkoxy or aryloxy groups were synthesized and employed for the cationic polymerizations of isobutyl vinyl ether (IBVE) in conjunction with HCl‐IBVE adduct. Living polymerizations were feasible with the titanium chlorides [TiCl2(OR)2] disubstituted with isopropoxy or phenoxy groups in CH2Cl2 at −15°C. The meso (isotactic) contents of the polymers obtained with TiCl2(OR)2 at −78°C became larger (up to 86%) with bulkier o‐substituents of phenoxy groups on the titanium compounds.
Synthetic applications of non‐polymerizable monomers in living carbocationic polymerization; recent developments
Authors: Hadjikyriacou S. , Li D. , Bae Y. C. , Faust R.
Published: March 2011

Recent developments using non‐(homo)polymerizable monomers, for the synthesis of functional polymers and block copolymers by living cationic polymerization are discussed. The preparation of block copolymers based on IB and αMeSt or IBVE are reported using DPE capping followed by Lewis acidity moderation. The use of non‐polymerizable diolefins such as bis (diphenylethylenes) for in situ coupling of living chains is also discussed. Depending on the structure of the diolefin mono‐ or diaddition is observed.
Liquid crystalline block copolymers by sequential cationic or promoted cationic and free‐radical polymerizations
Authors: Galli Giancarlo , Chiellini Emo , Yagci Yusuf , Serhatli Ersin I. , Laus Michele , Angeloni Annino Sante
Published: March 2011

The scope for the study of the synthesis and properties of liquid crystalline (LC) block copolymers is briefly outlined. While there are many approaches to the synthesis of LC block copolymers, the use of azo macroinitiators is very versatile and allows one to produce diverse block copolymer architectures. Azo macroinitiators are prepared by cationic or promoted cationic polymerization of tetrahydrofuran (1) or cyclohexene oxide (2), and are then used to initiate the free‐radical polymerization of various methacrylates 3,4 or acrylates 5–9 containing mesogenic azobenzene or biphenyl units thereby yielding block copolymers. The AB or ABA block copolymers are microphase‐separated and form smectic and/or nematic mesophases similar to the respective LC homopolymers.
New materials from telechelic polyacetals
Authors: Goethals Eric J. , Walraedt Saskia R. , Han Xinghua , Trossaert Geert G. , Hartmann Patrick J.
Published: March 2011

Telechelic polyacetals, obtained by cationic ring‐opening polymerization of 1,3‐dioxolane (DXL) and 1,3‐dioxepane (DXP), have been used as building blocks for polymer materials. In the first part of this paper, the synthesis and the properties of networks based on polyDXL α,ω‐bis(methacrylates) are discussed. The second part deals with the synthesis and the properties of polyacetal polyurethanes. A thermoplastic polyurethane was prepared with poly(DXL‐co‐DXP) α,ω‐diol as soft segment and the combination butane‐1,4‐diol and hexamethylene diisocyanate as hard segment. Polyurethane networks were obtained from polyacetal polyols and diphenylmethane diisocyanate (MDI). Some physical properties of these new materials are reported.
Kinetic and thermodynamic control in the cationic copolymerization of cyclic ethers
Authors: Bednarek Melania , Kubisa PrzemysłAw , Penczek StanisłAw
Published: March 2011

Cationic copolymerization of tetrahydrofuran with ethylene oxide in the presence of diols proceeds, at the properly chosen conditions, with complete conversion of both comonomers and leads to telechelic oligodiols. These conditions are based on the simultaneous kinetic and thermodynamic control for two operating mechanisms namely active chain end and activated monomer mechanism. Kinetics of copolymerization and model reactions were studied. The ratios of rate constants of competing reactions, governing the copolymer composition, were determined and it was found, that the microstructure of the copolymer can be controlled at low conversion while at higher conversion the kinetics of the competing parallel reactions is not favourable for the formation of a regular copolymer, in contrast to the previously studied copolymerization of tetrahydrofuran with epichlorohydrin.
Anionic and coordination polymerization of 3‐butyrolactone
Authors: Lenz Robert W. , Jedlinski Zbigniew
Published: March 2011

Aluminoxane catalysts and anionic initiators can polymerize 3‐butyrolactone, 3‐BL, to high molecular weight stereoregular polymers. With the racemic monomer, [R,S]‐3‐BL, anionic polymerization with alkali metal complexes can form syndiotactic polymers and aluminoxane catalysts can form either highly isotactic, syndiotactic, or atactic poly‐3‐butyrolactone, P‐3‐BL, depending on the composition and method of preparation of the aluminoxane and the conditions of polymerization.
Effect of bulkiness and lewis acidity of aluminium compounds on the anionic polymerization of methyl methacrylate in toluene
Authors: Schlaad Helmut , Müller Axel H. E.
Published: March 2011

The bulkiness and the Lewis acidity of added aluminium compounds strongly affect the polymerization of methyl methacrylate in toluene at −78°C. The polymerization strongly deviates from ‘ideal’ first‐order kinetics, i.e. the first‐order time‐conversion plots are kinked at low monomer conversions. Additionally, for the more bulky and more Lewis‐acid aluminium alkyls, the time‐conversion plots show a further downward curvature. This curvature is not the result of a termination reaction because the polymers are free of side products like β‐ketoesters or vinyl ketone units. The molecular weight distributions and tacticities of the resulting polymers are also affected. Dependent on the aluminium compound used, molecular weight distributions are in the range of 1.2 < Mw/Mn < 7, and the triad tacticity of the polymer can change from highly syndiotactic over atactic or heterotactic to highly isotactic.
Synthetic approaches towards new polymer systems by the combination of living carbocationic and anionic polymerizations
Authors: Feldthusen Jesper , Iván Béla , Müller Axel H. E. , Kops Jørgen
Published: March 2011

This study summarizes recent efforts to obtain by combination of living carbocationic and anionic polymerizations block copolymers which are potential precursors for building new well‐defined polymeric architectures with microphase separated morphology. Living carbocationic polymerization (LCCP) yields telechelic polyisobutylene (PIB) chains with a variety of useful endgroups, such as tert‐chlorine, isopropenyl, primary hydroxyl, tolyl etc. When tolyl‐ended PIB was used as precursor for macroinitiator of living anionic polymerization of 2‐(tert‐butyldimethylsilyloxy)ethyl methacrylate (tBuMe2SiOEMA), mixtures of homopolymers and block copolymers were formed due to incomplete lithiation of this chain end. In another approach a new functionalization method was developed by end‐quenching living PIB chains with 1,1‐diphenylethylene (DPE). In the presence of BCl3 a new telechelic PIB with 2,2‐diphenylvinyl (DPV) endgroups was formed. A corresponding DPV model compound was synthesized from 2‐chloro‐2,4,4‐trimethylpentane (TMPCl). Because of steric hindrance less than quantitative lithiation of this material occurred. Controlled deprotection of PtBuMe2SiOEMA obtained by living anionic polymerization (LAP) was utilized to prepare a precursor network composed of partially deprotected PtBuM2SiOEMA and hydroxyl‐telechelic PIB by using a diisocyanate crosslinker. After network formation deprotection with HCl was completed and a new amphiphilic network (APN) containing PIB and poly(2‐hydroxyethyl) methacrylate) (PHEMA) segments crosslinked by urethane linkages was obtained.
Synthesis of triblock copolymers made of a fluorinated central block and two outside poly(1,3‐dioxolane) blocks
Authors: Djebar Abdelkader , Reibel Léonard , Franta Emile
Published: March 2011

Conditions are given that allow the preparation of highly amphiphilic triblock copolymers where the central block is a perfluoropolyether (number average molar mass equal to 2000) only soluble in freon‐type solvents, and the outside blocks are made of water soluble poly(1,3‐dioxolane) whose molar mass can be controled by the amount of 1,3‐dioxolane consumed. Two methods are described: it is possible either to use CH2Cl2 as a solvent (but only one of the two phases yields the expected product) or to recourse to a Fomblin‐rich fraction prepared previously as the initial diol (but the product of the reaction can be heterogeneous and separation has to be performed).
Novel supramolecular catalysis in the controlled synthesis of polymers and block copolymers
Authors: Jedliński Zbigniew
Published: March 2011

Novel carbanionic polymerization of vinyl monomers as styrene, methyl methacrylate, as well as ring opening polymerization of oxiranes and lactones mediated by supramolecular complexes of alkali metals is demonstrated.
Stopped‐flow investigation of the cationic oligomerization of trans‐1,3‐diphenyl‐1‐butene initiated by trifluoromethanesulfonic acid in dichloromethane
Authors: Vairon Jean‐Pierre , Charleux Bernadette , Rives Alain
Published: March 2011

Reaction of trans 1,3‐diphenyl‐1‐butene (D), the trans ethylenic dimer of styrene, with trifluoromethanesulfonic acid in dichloromethane has been performed at temperatures lower than room temperature using a stopped‐flow technique with real time UV‐visible spectroscopic detection. The main product of the reaction was the indanic dimer of D. A transient absorption at 340 nm has een assigned to 1,3‐diphenylbutylium, a model for the polystyryl cation. Other absorptions at 349 nm and 505 nm have also been observed and were assigned to an allylic cation, 1,3‐diphenyl‐1‐buten‐3‐ylium, resulting from hydride abstraction from D. This species was very stable at temperatures lower than −30°C. A general mechanism was proposed based on a kinetic study of the involved reactions.
Physical aging phenomena in silica and glass beads filled elastomers (EPDM)
Authors: Haidar B. , Salah Deradji H. , Vidal A. , Papirer E.
Published: March 2011

The physical aging concept is generally used to explain the typical behavior of amorphous glassy materials such as amorphous polymers. It can be easily evidenced by measuring the effect of a static deformation on the dynamic mechanical properties. In this paper, an attempt is made to determine the “glassy” behavior of elastomeric EPDM chains when they are confined in the vicinity of the filler (glass beads, silicas) surface. It is demonstrated that glassy behavior and physical aging phenomena are detected even with a filled elastomer. Furthermore, the influence of the filler volume fraction, the filler nature and of filler surface treatments with silanes were studied. Finally, an original attempt is made to explain filler‐rubber reinforcement by a kind of bimodal network created from linkages between a densely packed interfacial region and the outer loose matrix.
Failure mechanics in thermoplastics filled with inorganic filler and elastomer inclusions: Experiments and modeling
Authors: Jancar J.
Published: March 2011

Elastic and viscoelastic moduli, yielding and failure of ternary composites of thermoplastic matrix filled with particulate fillers and elastomer inclusions are discussed. Modeling of the role of elastomer interphase in elastic response and in failure processes, based on the combination of numerical method (Finite Element Analysis) and percolation concept, is presented for PP/EPR/filler systems. Proposed expressions for Young modulus, yield strength and critical strain energy release rate are used to predict the lower and upper limiting values of these properties in the case of the two limiting morphologies. Good agreement is found between theoretical predictions and experimental data.
The application of hydrated mineral fillers as fire retardant and smoke suppressing additives for polymers
Authors: Hornsby Peter R.
Published: March 2011

The characteristics of hydrated mineral fillers are discussed with reference to their use as fire retardant additives for polymers. Particular consideration is given to their mode of action and criteria which influence their performance, both in reducing polymer flammability and in suppressing smoke evolution during combustion. Methods for reducing their adverse effect on mechanical properties of the host polymer are also highlighted.
Production of carbonates and hydrates and their use as flame retardant fillers
Authors: Rothon Roger N.
Published: March 2011

Flame retardant fillers are of growing importance as they do not give the high smoke and corrosive gas emissions associated with some other flame retardants The basic characteristics of a flame retardant filler are described, together with the manufacture of the principal commercial types. Experimental results are presented to demonstrate that their flame retardant effect is more complex than predicted by a simple endothermic decomposition model.
Fatigue behaviour of filled polymers
Authors: Trotignon Jean Pierre , Tcharkhtchi Abbas
Published: March 2011

The fatigue resistance of any material is the combined resistance to crack initiation and then to crack propagation.

1) In most of the cases, fillers act as strong cracks initiators. The Fatigue Crack Propagation can, under certain conditions, be improved (glass beads in epoxy) and this can be attributed to the crack front pinning mechanism. This mechanism is mainly governed by interparticle distances.

2) The number of particles per volume unit and thus the interparticles distance seems to be a key factor for endurance resistance. Thus, for a given number of particles per volume unit, the fatigue lifetimes are in good correlation with the FCP data.

3) A very rigid bounding between fillers and matrix is not necessarily good in terms of fatigue lifetime. A rubbery interphase can accommodate the deformation around the particle and thus can avoid a crack nucleation.
Hydrophobized polysaccharide macrogel formed by addition of surfactants
Authors: Deguchi Shigeru , Akiyoshi Kazunari , Lindman Björn , Sunamoto Junzo
Published: March 2011

Solution properties of an aqueous mixture of cholesterol‐bearing pullulan (CHP) and an ionic surfactant, sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium chloride (DoTAC), were studied. The mixture forms gel or sol depending on the polymer‐surfactant composition. Because the unmodified pullulan/surfactant/water mixture does not show any gel formation at all over the composition range studied, the hydrophobic cholesterol moieties play an essential and important role in the gel formation. The phase behavior could be interpreted by formation of mixed micelles between cholesterol moieties of CHP and the surfactants. This was supported also by SAXS studies in the sol region. Rheological measurements of the gel showed that viscoelastic response of the CHP/SDS gel was controlled by at least two different processes with shorter and longer relaxation times. This was different from previously reported results for a system such as hydrophobically modified (hydroxyethyl)cellulose (HMHEC) and SDS.
Amphoteric poly(vinyl alcohol) gel as a force generator: Observation of microporous gel formation with cryo‐SEM
Authors: Suzuki Makoto , Tateishi Tetsuya , Matsuzawa Masahiko , Saito Masakatsu
Published: March 2011

Amphoteric PVA hydrogels were made from mixed aqueous solutions of poly(acrylic acid), poly(allylamine) hydrochloride and poly(vinyl alcohol) by repetitive freezing and thawing. The hydrogen bond induced gelation produced an elastic and tough microporous hydrogel which generated tension as high as 0.3MPa corresponding to the solvent exchange from water to acetone. In this paper we show the microscopic structure of hydrogels determined by means of cryo‐SEM technique and X‐ray analysis.
Polysaccharide gels for colon targeting
Authors: Brøndsted Helle , Hovgaard Lars
Published: March 2011

Polysaccharides appear to have a potential as drug carriers for site‐specific drug delivery to the colon due to the well‐known fermentation of polysaccharides by the anaerobic microflora in the colon. This paper gives a short presentation of the rationale of colon‐specific drug delivery and briefly describes various in vitro and in vivo methods for testing of polysaccharide gels for colonic drug delivery. The application of dextran hydrogels is used as an illustrative example of a polysaccharide based colonic drug delivery system.
Gelation and aggregation of mucin in relation to the stomach's protective barrier
Authors: Bansil Rama , Cao Xingxiang , Bhaskar K. Ramakrishnan , Lamont J. Thomas
Published: March 2011

Dynamic light scattering was applied to study the effects of pH and concentration on pig gastric mucin. At low concentration (C = 2.0 mg/ml), the distribution of diffusion constants is independent of pH, with an average diffusion constant D = 4 × 10−8 cm2/s. At pH2, very large aggregates with 100‐time slower D (2 × 10−8cm2/s) are seen. Depolarized DLS can be observed at pH2 even at low concentration (C = 5.0 mg/ml). The rotational and translational diffusion constants were analyzed using the Kirkwood‐Riseman model for rods and show that at pH2 mucin is a rod‐like molecule of length 390 nm, diameter 55 nm, with an axial ratio (length/diameter) of 7. However, at pH7, no significant depolarized signals could be detected at any of the concentrations examined in the study. These results suggest that the mucin monomer undergoes a conformational change from a flexible to a rod‐like conformation upon lowering pH from 7 (neutral) to 2 (acidic). Such conformational change and aggregation of the gastric mucin molecule at acidic pH may provide a mechanism by which the gastric mucin layer prevents the stomach from digesting itself, since the back diffusion of acid from the lumen to the gastric epithelium is retarded by the gel layer.
Hydrogels and vascular grafts‐state of the art and beyond
Authors: Zdrahala Richard J.
Published: March 2011

Vascular grafts represent significant part of implantable medical devices. While the autologous grafts utilizing saphenous veins are used exclusively in cardiac artery bypass graft (CABG) procedures and in peripheral indications, polymer‐based grafts are widely used to replace diseased vasculature with internal diameter above 6 mm. The PET yarn is either knitted or woven into tubes of controlled patterns and porosity. The PTFE tubes are expanded into porous conduits (ePTFE) and the polyurethanes are spun, wound, dipped and foamed to produce porosities most suited for the healing. This porosity causes the blood to leak through the graft wall or at anastomosis through the suture holes. Both the wall leakage and suture hole bleeding remain rather serious drawbacks. Currently, collagen, gelatin, albumin and their derivatives are used as sealants. Various modes of application and degree of crosslinking are utilized to control in vivo degradation and graft healing. Enhancement of graft patency via improvement of initial hemocompatibility could be achieved by application of bioactive coatings. Heparinized systems seem to dominate in this field but many new concepts are being investigated. Intraluminal endothelization via endothelial cells seeding and mediating biologicals will open significant potential for synthetic grafts with ID well below 6 mm. Porous biodegradable tubes could be used as temporary scaffold to attract and promote cell propagation and ingrowth, the true angiogenesis. High‐swelling hydrogels could play a significant role both as sealants and modifiers of graft bioperformance. This paper discusses concepts and potentials needed for patent “small caliber” graft.
Interaction of cells with polymers
Authors: Smetana Karel , Vacík Jiří , Dvořánková Barbora
Published: March 2011

This paper summarizes the results of our experiments studying the effect of functional chemical groups of synthetic hydrophilic polymers on the recognition of these materials by macrophages in in vivo experiments. The interaction of keratinocytes with synthetic hydrophilic polymers in vitro is also demonstrated. The implants containing anionic groups (carboxylates) were shown to be better tolerated by nonspecific immunity. The keratinocytes are able to grow on hydrophilic polymer supports and migrate to surfaces with improved adhesivity (in vitro). The clinical applications of these experiments are demonstrated.
Thermally reversible polymer gels for biohybrid artificial pancreas
Authors: Vernon Brent , Gutowska Anna , Wan Kim Sung , Han Bae You
Published: March 2011

As an approach to replacing islets of Langerhans in an implanted biohybrid artificial pancreas, thermally reversible polymers based on N‐isopropylacrylamide were synthesized and then evaluated as an extracellular matrix for islets in an immunoprotecting membrane pouch. A high molecular weight poly(N‐isopropylacrylamide‐co‐acrylic acid (2 mole % in feed)) demonstrated gelation at 37°C and became a solution below 30°C. This polymer exhibited minimum syneresis (water separation) upon gelation from a solution state when the temperature was raised from room temperature to 37°C, while poly(N‐isopropylacrylamide) exhibited considerable syneresis under the same conditions. These properties influence the efficiency of islet entrapment. The copolymer was able to entrap rat islets almost 100%, but the homopolymer entrapped less than 50%. The static insulin secretion of the islets in the copolymer matrix at high glucose concentration (16.5 mM) was comparable to that of control islets, however, the entrapped islets showed prolonged viability in vitro. These results indicate the potential of developing a rechargeable biohybrid pancreas using thermally reversible polymer gels.
Collapse in responsive hydrogels
Authors: ilavský Michal
Published: March 2011

The swelling and mechanical behaviour of ionic poly(acrylamide) networks formed using both positively and negatively charged crosslinkers or acrylamide quaternary ammonium salt of various alkyl lengths as comonomers is reviewed. The effect of the charge concentration, its polarity, crosslinking density and the strength of hydrophobic interactions (proportional to the alkyl length) on the occurrence and the extent of the first‐order phase transition is discussed. The results are compared with the theory describing the swelling equilibria in polyelectrolyte networks.
Surface reorientation of hydrogels based on methacrylate copolymers
Authors: Lukáš Jaromír , Sodhi Rana N.S. , Sefton Michael V.
Published: March 2011

Surface molecular structures of two statistical copolymers, poly(2‐hydroxyethyl methacrylate‐co‐butyl methacrylate) (HEMA‐co‐BMA) and poly[2‐(2‐ethoxyethoxy)ethyl methacrylate‐co‐butyl methacrylate] (EOEOEMA‐co‐BMA), were studied by X‐ray photoelectron spectroscopy (XPS). Besides the classical “dry” XPS technique, where the polymer samples were air‐dried, also “deep‐freezing” technique was used, where the samples were investigated in deep‐frozen hydrated state. The differences in results obtained by the two techniques are discussed from the point of view of the polymer surface chain reorientation in response to various environment. The reverse polymer chain reorientation from the hydrated towards dry state was also followed.
Liquid chromatography of macromolecules at the point of exclusion — Adsorption transition. Principle, experimental procedures and queries concerning feasibility of method
Authors: Berek D.
Published: March 2011

Liquid Chromatography of macromolecules at the Point of Exclusion‐Adsorption Transition (LC PEAT) called also liquid chromatography under critical conditions of adsorption or liquid chromatography at the critical point of adsorption is a new and rapidly developing technique that ‐ in combination with some other LC separation procedures ‐ allows separation and molecular characterization of many complex polymer systems as polymer blends, interpolymers or functionalized oligomers. In this critical discussion review, the principles of LC PEAT are briefly elucidated and the nomenclature of some terms connected with the technique is proposed. The most important experimental procedures as eluent and column packing selection are described in detail. The weakpoints of method are discussed in terms of the sensitivity of results towards minute eluent composition, temperature and pressure changes, as well as towards both chemical and physical structure of separated macromolecules and column packing used. The peak broadening, skewing and splitting that often accompany the LC PEAT experiments are also outlined. Above ‐ mentioned, so far mostly overlooked problems may lead to limited repeatability of results and to low sample recovery, especially at higher polymer molar mass values, thus causing queries concerning the broader applicability and experimental feasibility of method, on the other hand these problems can also be regarded as a challenge to both theoreticians and experimentalists who can substantially contribute to the improvement of this powerful method ‐ and thus to its widespread application.
Compositional characterization of styrene copolymers by non‐exclusion liquid chromatography
Authors: Mori Sadao
Published: March 2011

Recent advances in high‐performance liquid chromatography enable us to separate synthetic copolymers according to composition. Several techniques for non‐exclusion liquid chromatography (NELC) for polymers and copolymers are reviewed, focusing on the technique developed in our laboratory. Size exclusion chromatography in combination with NELC makes possible the accurate determination of both molecular weight distribution and chemical composition distribution of copolymers at the same time.
Separation of copolymers by adsorption liquid chromatography
Authors: Sato Hisaya , Ogino Kenji , Darwint Tri , Kiyokawa Iwao
Published: March 2011

Binary random copolymers of styrene with butadiene, methyl methacrylate, and t‐butyl methacrylate, and styrene‐methyl methacrylate‐acrylonitrile random terpolymers were separated by adsorption chromatography. The HPLC conditions required for the sample to adsorb to the stationary phase are discussed. Sequence length as well as composition affected the elution volume of block and graft copolymers of styrene and butadiene. A mixture of terpolymers having different composition was separated to each component by cross‐fractionation using two types of adsorption chromatography.
Control of polymer structure by chain transfer processes
Authors: Rizzardo Ezio , Chong Y. K. , Evans Richard A. , And Graeme Moad , Thang San H.
Published: March 2011

Chain transfer can be performed effectively by a mechanism of addition‐fragmentation with appropriately substituted allylic compounds, vinyl ethers and thionoesters. Selection of substituents allows the optimization of chain transfer activity and the preparation of macromonomers and other end‐functional polymers from acrylates, methacrylates, styrene and vinyl acetate. The addition‐fragmentation concept has been extended to the free radical ring‐opening polymerization of cyclic allylic sulfides.
The importance of exchange reactions in controlled/living radical polymerization in the presence of alkoxyamines and transition metals
Authors: Matyjaszewski Krzysztof
Published: March 2011

The role of exchange reactions in controlled/living radical polymerizations is analyzed. Styrene polymerization in the presence TEMPO and atom transfer radical polymerization (ATRP) catalyzed by transition metals (CuIIX2/2Bipy complex) are compared. ATRP proceeds approximately one order of magnitude faster than TEMPO‐moderated polymerization due to a higher stationary concentration of radicals and an equilibrium more shifted to the side of radicals. ATRP can provide better defined polymers with polydispersities down to Mw/Mn≈1.05. This fact can be ascribed to a faster deactivation process and a smaller contribution of side reactions. The polydispersities in both systems are defined by the relative rates of the deactivation and propagation processes. The rate constant of deactivation of growing polystyryl radicals by TEMPO is in the range of kd≈108 mol−1·L·s−1, which is substantially higher than the previously reported value.
Initiation of free radical polymerization by thermal cleavage of carbon‐carbon bonds
Authors: Braun Dietrich
Published: March 2011

Free carbon radicals for initiation of polymerization processes can be generated either by light‐induced fragmentation or by homolytic thermal dissociation of suitable compounds. For thermal initiation of polymerization processes beside azo, peroxy and some other thermolabile compounds also alkanes with highly substituted carbon‐carbon bonds are capable. The reason why this interesting class of initiators, even more than 100 years after their discovery, has found only limited applications in radical polymerization is caused by their special mechanism of chain reaction initiation. The formed and in most cases highly resonance‐stabilized substituted alkyl radicals are not very reactive against monomers like methyl methacrylate or styrene but more against growing macroradicals. Therefore, during the initiation step at rather high primary radical concentrations only low‐molecular oligomers with two alkane end groups are formed. Under special conditions this process is reversible, whereas in some other cases the reaction can be described as a “dead end” polymerization. The oligomers which were formed e.g. in the case of methyl methacrylate polymerization with tetraaryl butane dinitriles are able to re‐initiate the polymerization process similar as in a living polymerization which can be used for the synthesis of block copolymers. Mechanism, kinetics and possible applications of such alkane‐initiated polymerizations are discussed.
Free‐radical polymerization in micellar media: Effect of microenvironment
Authors: Candau Françoise , Volpert Edgar , Lacik Igor , Selb Joseph
Published: March 2011

A micellar polymerization process has been used to prepare polyacrylamide or poly(acrylic acid) hydrophobically modified with low amounts (1–5 mol%) of an N‐alkyl‐ or N‐alkylarylacrylamide. The effect of the initial monomer segregation on the copolymer microstructure and the copolymerization mechanism has been investigated. This method leads generally to multiblock copolymers in which the number and length of the hydrophobic blocks vary with the initial number of hydrophobes per micelle. Interestingly, the copolymerization of acrylamide with disubstituted acrylamides leads to homogeneous samples with an average copolymer composition independent of the degree of conversion, in contrast to what is observed with monosubstituted acrylamides for which a drift in composition is observed. The difference in polarity between the bulk phase and the micellar phase is responsible for this behavior. This microenvironment effect modifies the reactivity ratios of those hydrophobes capable of forming hydrogen bonds, whereas the reactivity of the other hydrophobes remains unaffected.
Polymerization of water soluble cationic vinyl monomers
Authors: Jaeger Werner , Hahn Mathias , Lieske Antje , Zimmermann Arvid , Brand Fabien
Published: March 2011

This paper summarizes investigations on the radical polymerization of cationic vinyl monomers with respect to the peculiarities of the reaction in aqueous solution, the synthesis of model polymers and polyelectrolytes with regular structure as well as to a new process of stabilized precipitation polymerization. The rate of polymerization depends on the ionic strength of the solution. Random copolymers of diallyldimethylammonium chloride and acrylamide with variable charge density but equal molecular weight were synthesized by a feeding technique. Block copolymers consisting of charged and uncharged monomelic units with different hydrophilicity are available using macroazoinitiators. The novel polymers are powerful stabilizers in the precipitation polymerization of water soluble cationic vinyl monomers in aqueous salt solution leading to a dispersion of fine polymer particles. Polyampholytes with alternating positively and negatively charged monomelic units in the backbone were obtained by cyclocopolymerization of diallylanmine compounds and derivatives of maleic acid.
Recent developments in miniemulsion polymerization
Authors: Aizpurua Imanol , Amalvy Javier , Barandiaran Maria J. , De La Cal José C. , Asua José M.
Published: March 2011

Some developments in miniemulsion polymerization aiming at taking advantage of its unique mechanisms minimizing the drawbacks of this technique are discussed. The discussion includes preparation of highly concentrated latexes, miniemulsion polymerization in continuous stirred tank reactors (CSTRs), and elimination of the low‐molecular‐weight hydrophobe.
Reactivity in radical polymerisation: An improved method for the prediction of monomer reactivity ratios and transfer constants
Authors: Jenkins Aubrey D. , Jenkins Jitka
Published: March 2011

Half a century after the Q‐e scheme was promulgated, a substantially improved method for predicting monomer reactivity ratios and transfer constants has been developed from the Patterns of Reactivity scheme. It is based on the same premise as its predecessors, that reactivity is controlled partly by thermodynamic and partly by polar factors, but the new treatment yields values much closer, on average, to the reported experimental data.
Stationary and non‐stationary processes in non‐classical radical polymerization with size dependent termination
Authors: Bamford Clement Henry
Published: March 2011

Kinetic analysis of non‐classical radical polymerization is discussed in terms of the Group‐Termination Procedure on the basis of the geometric mean approximation. Expressions for important kinetic functions of stationary reactions, with or without chain‐transfer, are listed and compared with their classical counterparts. In the treatment of non‐stationary reactions (with or without transfer) special attention is paid to the calculation of pre‐ and after‐effects and their applications in the evaluation of absolute rate coefficients.

Nomenclature: I = rate of chain initiation. R·r = concentration of radicals of size r. R· = total concentration of radicals = ΣR· r̄ = number‐average radical size.

v = mean kinetic chain‐length

τ = mean lifetime of a kinetic chain.

ω = rate of polymerization (‐dM/dt).

Subscripts 1,2 applied to the above signify values at the beginning or end, respectively, of a non‐stationary period.

kfL = rate coefficient for chain‐transfer to species L l = kfLL/kpM

V = j/kpM + lR

a = (jk)½/(kpM); b = a/(1+l).

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To simplify the presentation concentration brackets are omitted. Conventional mol, dm3, s units are assumed throughout.
Kinetics of long‐chain branching in emulsion polymerization
Authors: Mazzotti Marco , Fiorentino Stefano , Ghielmi Alessandro , Morbidelli Massimo , Storti Giuseppe
Published: March 2011

A kinetic model suitable to deal with the case of branched polymers produced in emulsion both in the case of chain transfer to polymer and propagation to terminal double bond is briefly presented and numerically solved through the method of the moments. Thanks to the “numerical fractionation” approach, the whole molecular weight distribution of the polymer is evaluated while accounting for the compartmentalized nature of the system. The results of some illustrative calculations concerning the effects upon the molecular properties of the final polymer of starved semibatch monomer feed policies, addition of a chain transfer agent and propagation to terminal double bond are discussed.
Free‐radical polymerization kinetics in extended ranges of temperature, pressure and monomer conversion
Authors: Buback Michael
Published: March 2011

Free‐radical polymerizations have been studied within extended ranges of pressure, temperature, and monomer conversion, including reactions in supercritical phase, where polymerization rate and polymer properties may be continuously tuned. The methods by which propagation (kp) and termination (kt) rate coefficients of homopolymerizations may be determined as a function of P and T, partly up to 3000 bar and 250 °C, are based on using pulse lasers for inducing polymerization (PLP) either in conjunction with size exclusion chromatography (SEC), for kp measurement, or in conjunction with online spectroscopic analysis of monomer conversion, for kt/kp measurement. With kp from PLP‐SEC, the kt/kp data allow to deduce also individual rate coefficients for the termination step. kp primarily depends on temperature and pressure with the values being close to each other within a monomer family, such as the acrylic ester or the methacrylic ester family. Termination rate, which refers to a radical‐radical process, depends on P, T, monomer conversion, solvent type, and on chain length. The major changes of kt with conversion are illustrated using a model that takes segmental diffusion, translational diffusion, and reaction diffusion into account.
The importance of accurate and precise molecular weight measurement in pulsed‐laser polymerization
Authors: Davis Thomas P. , Zammit Michael D.
Published: March 2011

Molecular weight distributions generated by pulsed‐laser polymerization have been determined experimentally using multi‐detector size exclusion chromatography (SEC). The conditions for accurate and precise SEC have been defined. The importance of the inter‐detector delay (IDD) is stressed and two different methods of defining IDD are compared. In addition this work highlights the problems associated with the use of Mark‐Houwink constants in constructing a universal calibration curve. Some preliminary results obtained from matrix‐assisted‐laser‐desorption‐ionisation mass spectrometry are also presented.
Polymeric photoinitiators as a tool for clarifying mechanistic aspects of free‐radical polymerization
Authors: Carlini Carlo , Angiolini Luigi , Caretti Daniele , Corelli Elena
Published: March 2011

Polymeric photoinitiators, based on side‐chain benzoin methyl ether moieties differently anchored to the backbone, have been designed and applied to the UV cure of acrylic formulations for clarifying the role played by benzoyl and α‐alkoxybenzyl primary radicals in the polymerization process. Kinetic data on the photocuring processes, in the presence of the above polymeric systems, as compared with those obtained by using the corresponding low‐molecular‐weight structural models, are presented and interpreted in terms of different reactivity of the two types of primary radicals towards initiation and termination steps of the polymerization process.
Applications of the study of end‐groups. A new approach to the determination of transfer constants
Authors: Bevington John C. , Hunt Barry J. , Barson C. Anthony
Published: March 2011

A summary is given of established procedures depending on analyses of polymers for initiator fragments incorporated as end‐groups; attention is paid to determinations of kinetic chain lengths and rates of initiation in polymerizations and also of the relative importances of combination and disproportionation during termination. Recent developments allow determination of transfer constants from information on the average number of initiator fragments in a molecule of a polymer, even in some cases where the transfer is degradative. Their applications are discussed for various transfer agents including iodoform and derivatives of propene from which allylic radicals could be produced. There is consideration of the possibilities of applying analyses for initiator fragments to study of transfer initiator, transfer to polymer and primary radical transfer.
The reactor polymer alloys: The shifting of the frontier of polymer research
Authors: Galli Paolo
Published: March 2011

The discovery (1968) of the high yield Ziegler‐Natta catalysts based on active MgCl2 was the beginning of a scientific and industrial revolution that has brought about the creation of superactive, isospecific, spheriform fourth generation catalytic systems. The rationalization of the polymer/catalyst replication phenomenon and the understanding of the catalyst “architecture” effects on polymer shape and morphology has led to the exploitation of the “Reactor Granule Technology”. This has made the generation of a broad range of homo, copolymers and multiphase alloys (Catalloy) possible by synthesis, most of which having a previously unobtainable spectrum of performance (Refs. 1,2,3). The reactor granule technology concept has also been the basis for the achievement of a family of polyolefin/non polyolefin alloys with engineering properties.

More recently, the reactor granule approach has been extended so as to couple the advantages of both heterogeneous and homogeneous metallocene catalysts (mixed catalysis), thus allowing the synthesis of a very new family of “in situ” polyolefin alloys.
Application of equation of state theories to poly(styrene‐Co‐acrylonitrile)/poly(methyl methacrylate) blends
Authors: Rudolf Bernd , Ougizawa Toshiaki , Shimomai Ken , Higashida Noboru , Inoue Takashi , Kressler Jörg
Published: March 2011

The miscibility behavior of poly(styrene‐co‐acrylonitrile)/poly(methyl methacrylate) blends was described by using the equation of state theory of Flory et al. and the lattice fluid theory. The ‘surface area effect’ inherently included in the latter theory was neglected. For that case it is found that the description of the phase behavior of that theory is similar then to that obtained by using the theory of Flory et al. Without neglecting this surface area effect, however, it is not possible to describe the observed behavior with the lattice fluid theory. Moreover, for both theories it is necessary to include both, interactional and free volume effects, though the observed LSCT behavior is not solely due to free volume effects.
Calculation of miscibility behavior of multinary polymer blends
Authors: Horst Roland , Wolf B. A.
Published: March 2011

A method for the calculation of phase diagrams (tie lines and binodal, spinodal, critical points and their stability) based exclusively on the Gibbs energy of mixing, δG, is presented which does not require the calculation of the derivatives with respect to the composition. The method is demonstrated for ternary mixtures of two homopolymers and the corresponding copolymer, and for quaternary and quinternary blends of five polymers exhibiting a closed miscibility gap. The advantages of the presented method become most obvious in the mathematical description of measured phase diagrams, where complex composition dependencies of the interaction parameter are observed.
Phase separation in thermoplastic ‐ thermoset polymer blends
Authors: Elliniadis Stavros , Higgins Julia S. , Choudhery Riaz A. , Jenkins Stephen D.
Published: March 2011

The effect of composition, curing temperature and curing agent on the phase separation of a blend containing poly‐ethylene‐terephalate and diglycidyl‐ether of bisphenol A was studied using a small angle light scattering(SALS) technique. The results show a wide compositional range for the spinodal decomposition mechanism and the potential for greater morphology control in this type of blends.