bluuebunny/crossref_metadata_2025 huggingface dataset:
Swelling and scattering investigations on chemically cross‐linked poly(vinyl alcohol) hydrogels
Authors: Horkay Ferenc , Burchard Walther , Geissler Erik , Hecht Anne‐Marie , Zrinyi Miklós
Published: March 2011

Swelling and scattering measurements are reported from chemically cross‐linked polyvinyl alcohol) hydrogels and the corresponding semi‐dilute polymer solutions. The mixing free energy in the swollen network is found to be significantly smaller than that of the corresponding polymer solution at identical concentration. Static light scattering and small‐angle neutron scattering measurements indicate the presence of large‐scale static structures in the solution. Reasonable agreement is found between the osmotic moduli obtained from light scattering measurements and macroscopic osmotic observations.
On the scattering by polymers and copolymers at high angles
Authors: Benoît H.
Published: March 2011

In this paper we discuss the interpretation of the large angle scattering for chains, either being rod like, rigid or presenting excluded volume effect. It is shown that on highly branched polymers one can obtain a parameter which depends on the functionality of the crosslinks and on the average length of the blocks in the chain. One shows also how this type of analysis allows the interpretation of neutron results during transesterification.
Dynamic and static light scattering by weakly ionized gels and solutions
Authors: Candau Sauveur J. , Moussaïd Abdellatif , Joosten Jacques G. H.
Published: March 2011

Dynamic light scattering (DLS) and static light scattering (SLS) experiments have been performed on partially neutralized poly(acrylic acid) and poly(methacrylic acid) solutions and gels. The gels exhibit a non‐ergodic behavior, much less marked however than that observed in neutral systems. By combining DLS and SLS, the fluctuating part of the light scattered from PAA gel was separated from the total scattered intensity and found to be almost equal to the intensity scattered by the solution. Also the diffusion coefficient associated with the dynamic fluctuation was found to be the same in the PAA gel and the PAA solution.
Dynamic viscoelastic comparison of chemical and physical gels
Authors: Yu Qun , Amis Eric J.
Published: March 2011

The dynamic viscoelastic behavior of TEOS (tetraethoxysilane) and gelatin during the sol‐gel transition is compared. Different profiles of dynamic storage modulus G″ and loss modulus G″ with time are seen. Gelation time tgel is determined from the frequency independent tan δ = G″/G' for both systems. During the period following the gelation point, a transition in the scaling exponent of G' with (t ‐ tgel) is seen. For TEOS, the exponent changes from 0.494 to 5.24; for gelatin, from 0.24 to 2.11. The percolation model is used to qualitatively explain the differences in different networks.
Computer simulation of the formation of polymer networks
Authors: Akgiray Omer
Published: March 2011

Complex crosslinked polymer structures can be quite easily modeled with the aid of computers. BTOSYM's implementation of an algorithm that has been developed by Eichinger and his co‐workers over the last few years is described. This algorithm allows us to model both random (as in sulfur‐cured rubber) and site‐specific (as in end‐linked silicones) crosslinking reactions. The simulation method provides detailed information on gel points, cycle rank, modulus of elasticity and other characteristics of the networks as they are formed. Illustrative results obtained with the program are presented.
A nuclear magnetic resonance study of molecular anisotropy in strained networks and network blends
Authors: Brereton M. G.
Published: March 2011

The splitting of the nuclear magnetic resonance line, seen in strained networks, is shown to originate from the anisotropic screening of the excluded volume interaction by density fluctuations. In a blend concentration fluctuations also contribute to the screening and are greatly enhanced if the phase separation point is approached. The effect on the line shape has been calculated and is shown to be sensitive to the thermodynamics of the phase separation.
Inhomogeneous biopolymer gels
Authors: Stading Mats , Langton Maud , Hermansson Anne‐Marie
Published: March 2011

The microstructure and rheological behaviour of inhomogeneous biopolymer gels was studied using a model system of β‐lactoglobulin. It can form both fine‐stranded and particulate gels which can be homogeneous or inhomogeneous depending on pH and heating rate. The dense and loose regions of the fine‐stranded gels had different relaxation times which significantly influenced the mechanical spectrum. The particulate gels showed coarser inhomogeneities influencing the fracture properties of the gels.
Synthesis and properties of aramid dendrimers
Authors: Backson S. C. E. , Bayliff P. M. , Feast W. J. , Kenwright A. M. , Parker D. , Richards R. W.
Published: March 2011

The synthesis, characterisation and properties of simple low molecular weight aromatic amide dendrimers is described. The insights into the problems inherent in the synthesis of such systems provided by molecular modelling studies are discussed along with possible strategies for circumventing them. Preliminary results concerning blends of aramid dendrimers with poly(hexamethyleneadipamide) are presented.
Highly branched aromatic polymers prepared by single step syntheses
Authors: Kim Young H.
Published: March 2011

Highly branched polyphenylenes, polyphenylene ethers, aromatic polyesters and polyamides synthesized from AB2 type monomers are reviewed. Polyphenylenes were obtained by aryl‐aryl coupling reactions of 3,5‐dihalo‐phenyl organometallic reagents. 13C NMR indicates about 70% branching efficiency. A Tgat 236°C was observed, but the polymer did not form films. Polyethers were prepared by oxidative coupling of 2,4,6‐tribromophenol and 2,4‐dibromophenol. The former monomer gave high molecular weight polymers but the latter monomer did not polymerize well. Condensation of 3,5‐diaminobenzoic acid (I) and 3‐aminoisophthalic acid derivatives in an amide solvent gave lyotropic hyperbranched aromatic polyamides. The GPC indicated a large degree of polymer aggregation in the amide solvent in the absence of a complexing salt.
Metallo‐ and metalloido‐micellane™derivatives: Incorporation of metals and nonmetals within unimolecular superstructures
Authors: Newkome George R. , Moorefield Charles N.
Published: March 2011

Cascade polymeric architecture possessing internal functionalities was employed for the preparation of metallo‐ and nonmetallo‐MicellaneTM derivatives. Specifically, tetra‐ and dodeca‐o‐carborane superclusters, were obtained via treatment of the corresponding 1st and 2nd generation tetra‐ and dodeca‐alkyne, hydrocarbon cascade (MicellaneTM) derivatives with decaborane. Reaction of the same polyalkyne dendritic precursors with Co2(CO)8 afforded the benzyl protected, CobaltomicellanesTM possessing 12 and 24 internal metal centers, respectively. Control of amide‐based, carboxylic acid terminated macromolecular hydrodynamic radius via changes in solution pH was demonstrated. Heterocascade syntheses employing amide and metalligand monomer connectivity were accomplished. The relation of interior cascade reactivity to macromolecular “void volume” was examined.
New comb‐like polymers: Synthesis, structures and reactivity
Authors: Ritter Helmut
Published: March 2011

Comb‐like polymers have been widely investigated mainly to correlate their structures with the thermal behaviour. Our interests are directed on the synthesis of new types of comb‐like polymers bearing reactive groups in the side chains, main chain or as end groups. One part of the investigations deals with the behaviour of photosensible polymers containing azobenzene, cinnamic acid and mesoionic moieties. The use of enzymes as catalysts for the synthesis of new methacrylic derivatives and for the modification of polymers illustrates a fascinating contribution to polymer chemistry. The classical Diels‐Alder addition was also used for the synthesis and modification of polymers. Finally, the construction of polymers containing rotaxanes in the side chains is presented.
Polysilanes with various architectures
Authors: Maxka Jim , Chrusciel Jerzy , Sasaki Manabu , Matyjaszewski Krzysztof
Published: March 2011

Copolymers and homopolymers containing silicon atoms connected to three and four other silicon atoms have been prepared and characterized. We report the first evidence of dendritic polymers with silicon backbones. Copolymers made from RSiCl3 and R1R2SiCl2 resemble hybrid materials of polysilyne and polysilanes. Polymers, which contain tetrasilyl‐substituted Si atoms, [(SiMe2)4Si]n and (Si)m(Me2Si)n, have also been synthesized. These molecules appear to be the first hyperbranched polymers, which have applications based on their electronic properties. The properties of these molecules fit into the hierarchy of 1‐D to 3‐D topologies known for Si materials.
Synthesis and characterization of macrocyclic polystyrene block‐copolymers
Authors: Gan Yao‐Dong , Zöller Joachim , Yin Rui , Hogen‐Esch Thieo E.
Published: March 2011

The synthesis of macrocyclic polystyrene‐ block‐poly(2‐vinylpyridine) and macrocyclic polystyrene‐ block‐poly(dimethylsiloxane) was carried out by initiation of 2‐vinylpyridine (2VP) and hexamethyl‐cyclotrisiloxane (D3) by difunctional living polystyryllithium followed by coupling with 1,4‐bis(bromethyl)benzene (1,4‐DBX) and dichloro‐dimethylsilane (Cl2SiMe2), respectively. A small portion of the living ABA precursors were protonated to serve as isobaric linear precursors. The linear and macrocyclic block copolymers were characterized by size‐exclusion chromatography (SEC). The ratios of apparent cyclic/linear SEC molecular‐weight maxima versus degree of polymerization (DP) show increases with decreasing DP varying from 0.70 ± 0.03 at high DP ≤ 200 to 0.78 ± 0.044 at low DP (≥60) whereas that of the linear ABA block copolymers decreased. Increases in glass transition temperature (Tg) were also observed for the cyclic PS‐b‐PDMS copolymers with respect to the isobaric linear precursors. The macrocycles were characterized by 1H and 13C NMR and in the case of macrocyclic PS‐b‐PDMS by 29Si NMR as well. Broadening in the NMR absorptions of the macrocyclic block copolymers is general and is similar to that observed for the homopolymers. Differemtial scanning calorimetry (DSC) analysis of the PS‐b‐P2VP macrocycles shows increases in Tg at lower molecular weight as was observed for the PS and P2VP macrocycles.
Macro‐cyclic aramids (2n‐AZA[2n]paracyclophane‐2n‐ones):new intermediates for the synthesis of p‐aramids
Authors: Memeger Wesley , Lazar Joseph , Ovenall Derick , Arduengo Anthony J. , Leach Roger A.
Published: March 2011

An easy route to a new class of n‐azapara[2n] cyclophane‐n‐ones, N‐substituted p‐oriented cyclic aromatic amide (cycloaramid) oligomers, is described. The bulky diamine, N, N′‐di‐sec‐butyl‐p‐phenylenediamine is condensed with terephthaloyl dichloride at elevated temperature in o‐dichlorobenzene to provide a high yield of N, N′‐di‐sec‐butyl‐p‐phenyleneterephthalamide cyclic oligomers (from dimer to tridecamer). The cyclization is favored by the cis conformation of the N‐substituted amide bonds present in the growing chain. Ring opening polymerization of these new cycloaramids to high molecular weight linear polymers can be effected in the melt phase with highly nucleophilic catalysts, such as 1,3‐dialkylimidazole‐2‐thiones especially when an acid cocatalyst is employed. The N‐substituted polymers yield crystalline films and fibers with an axial repeat length which can only be explained by an unexpected trans conformation of the amide bonds. The facile synthesis of other macrocyclic amides by the steric control of macrocyclization by N‐substitution of the amide bond is also described.
Synthesis and hydrophobic binding studies on a water‐ soluble tritriptycene
Authors: Webster Owen W.
Published: March 2011

The water soluble tritriptycene 1 was synthesized starting with triptycene trisquinone and anthracene. The hydrophobic binding of substrates to the benzene‐walled cavities in 1 was studied by noting the up‐field shift of substrate protons in the NMR of the substrate in the presence of aqueous 1. Small substrates, negatively charged substrates or substrates larger than the cavities do not bind as strongly as substrates about the same size as the cavities or those bearing a positive charge. Based on differences in AHz'S, the bound substrates position themselves in the cavities so that polar groups are at the water interface.
Recognition and assembly using protein “building blocks”
Authors: McGrath Kevin P. , Kaplan David L.
Published: March 2011

A new approach to materials design is presented, utilizing specific recognition and assembly of proteins at the molecular level. The approach exploits the control over polymer chain microstructure afforded by biosynthesis to produce protein‐based materials with precisely defined physical properties. Incorporated into these materials are recognition elements that stringently control the placement and organization of each chain within higher order superstructures. The proteins, designated Recognin A2 through Recognin E2, are recombinant polypeptides designed de novo from both natural consensus sequences and an appreciation of the physical principles governing biological recognition. The synthesis and characterization of the protein recognition elements is briefly described and initial studies on self‐assembly‐recognition patterns using surface plasmon resonance and circular dichroism are presented. A subset of these materials are programmed to spontaneously assembly into complex, multicomponent structures and represent a first step in a rational approach to nanometer‐scale structural design.
Supramolecular architectures from phthalocyanine building blocks
Authors: van Nostrum C. F. , Nolte R.J.M.
Published: March 2011

Different procedures for preparing columnar stacks and layered structures from phthalocyanine molecules are presented and discussed, including organization of the molecules by one of the following means: (i) with the help of liquid crystallinity, (ii) by using crown ether rings attached to the phthalocyanine core, (iii) by polymerization, and (iv) by Langmuir‐Blodgett film formation.
Helix reversals as bad neighbors to liquid crystal organizations in cholesteric states and thermally reversible gels of poly(ALKYL isocyanates)
Authors: Green Mark M. , Khatri Chetan , Mark Herman F.
Published: March 2011

While the temperature dependence of the lyotropic cholesteric pitch of the single helical sense poly ((R)‐2,6‐dimethylheptyl isocyanate) is in line with theory, comparable data on this state produced by chiral doping of the lyotropic nematic state of poly(n‐hexyl isocyanate) could suggest an interplay between the supramolecular chirality of the liquid crystal and the dynamic equilibrium of the left and right hand helical blocks in this otherwise racemic polyisocyanate. The exclusion of helix reversals, as undersireable kinks in the liquid crystal organization, could play a role in this effect. Such helix reversal exclusions can also explain the peculiar chiral optical changes associated with the thermally reversible gelation of poly(n‐hexyl isocyanate) copolymers in hydrocarbon solvents. These gels likely arise by entering the broad biphasic region of the Flory phase diagram leading to the formation of liquid crystal aggregates.
Synthesis and physical properties of poly(aryl ether)s containing diphenylacetylene moieties
Authors: Strukelj Marko , Paventi Martino , Hay Allan S.
Published: March 2011

Poly(aryl ether)s containing diphenylacetylene moieties in the backbone have been synthesized. When the polymers are heated an exothermic reaction, resulting from reaction of the acetylene units, occurs in the range 380‐ 434°C and the polymers undergo a cross‐linking reaction. Polymers cross‐linked at 340°C exhibit Tg increases from 2°C to complete disappearance of the Tg depending on the concentration of the diphenylacetylene group which has been incorporated into the polymer. In most cases films of the cross‐linked polymers are still flexible and exhibit Young's moduli in the range 1.2‐2.1 GPa at 200°C. The solubility or the amount of swelling of these cross‐linked polymers in solvents depends on the mol % of diphenylacetylene groups incorporated in the polymer backbone. Copolymers have also been synthesized.
Living bimetallic initiators for the preparation of triblock copolymers
Authors: Novak Bruce M. , Deming Timothy J.
Published: March 2011

The compound [(η‐C3H5)Ni(OC(O)CF3)]2 (I), which has been used extensively as a butadiene polymerization catalyst and more recently as an isocyanide polymerization catalyst, has been successfully used in the preparation of polyisocyanide ‐ polybutadiene block copolymers. Since both monomer polymerizations are living, this block copolymer synthesis is highly versatile with respect to polymer segment chain lengths and the types of monomers used. Because non‐reciprocal end‐group activities prevent the preparation of triblock copolymers of the type polyisocyanide‐butadiene‐polyisocyanide, bimetallic initiators possessing two allylnickel moieties linked through a central core have been prepared and used to synthesize these desirable triblock copolymers. These materials have been characterized by using gel‐permeation chromatography, differential scanning calorimetry, 13C NMR and scanning electron microscopy.
Towards a molecular theory of polymer blends
Authors: Freed Karl F. , Dudowicz Jacek
Published: March 2011

The importance of including specific monomer structures, local correlations, and “equation of state effects” into the statistical thermodynamics of polymer blends is accomplished by developing and applying the lattice cluster theory. This new theory provides systematic corrections to Flory‐Huggins theory from local correlations and describes polymers as containing structured monomers that extend over several lattice sites.
Association of macromolecules and its influence on polymer miscibility
Authors: Kuleznev Valery N.
Published: March 2011

Experimental data are shown which confirm the existence of increased macromolecules association in a polymer mixture. The increase of association is revealed in the increase of light scattering intensity and the increase of density (local ordering increase). The grown up association degree determines the peculiarities of network formation through cross‐links in the solution of polymer mixtures. Macromolecules associates degrade under mechanical stresses or after addition of slight amounts of substances which are able to interact intensively intermolecularly (solvating) with macromolecules of one of the polymer components in the mixture. Representation of associates formation and degradation in polymer mixture help to explain many experimental data on thermodynamics, structure and properties of polymer mixtures.
Non‐equilibrium thermodynamical description of heterogeneous polymer systems (viii): New concept for understanding brittle‐to‐tough transition in polymer blends
Authors: Wessling Bernhard
Published: March 2011

A new model for impact modification in polymer blends is being presented. The new model is derived from the new non‐equilibrium thermodynamical description of heterogeneous polymer systems and is interpreting crazing fracture energy dissipation and fracture mechanism in a new way: on the basis of dissipative structures in polymer blends and their dynamics.
Interface formation between compatible polymers as determined by neutron reflectometry: PMMA and PVC
Authors: Kunz Klaus , Stamm Manfred
Published: March 2011

Initial stages of interdiffusion at the interface between two films of poly(methylmethacrylate) (PMMA) and poly(vinyl chloride) (PVC) have been determined by neutron reflectometry. Experiments are performed at temperatures between the glass transition temperatures of the homopolymers. PMMA chains are thus not mobile, but are dissolving in PVC. The growth of the interface width with time follows a power law, which depends on temperature, and the position of the interface moves in the direction of the immobile component. With a PVC film on top, the enrichment of PMMA at the free surface is observed at later times.
Phase diagram and thermal and mechanical properties of isotactic polypropylene/hydrogenated oligo(cyclopentadiene) blends
Authors: Cimmino Sossio , Martuscelli Ezio , Silvestre Clara
Published: March 2011

The system formed by isotactic polypropylene (iPP) and hydrogenated oligo(cyclopentadiene) (HOCP) is investigated in order to study the influence of the composition and thermal history on the morphology, phase structure, miscibility and thermal and mechanical properties of the blends. A phase diagram presenting both the lower and the upper cloud point curves is proposed. It is shown that these blends assume different morphologies and consequently present diverse thermal and dynamic‐mechanical behaviours depending on quenching processes from one‐phase region or two‐phase region. From the analyses of the results of optical microscopy, WAXS, DSC and DMTA techniques it is found that: blend films, quenched from the melt of one‐phase region to room temperature, contain one amorphous phase and iPP in smectic form; moreover they are transparent and possess a reduced permeability to oxygen and aroma; conversely when the samples are quenched from the melt of two‐amorphous phase region there is the formation of two amorphous phases (the iPP‐rich phase and the HOCP‐rich phase) and at room temperature the iPP crystallizes in the monoclinic α form.
Surface studies of polymer blends
Authors: Occhiello E. , Garbassi F.
Published: March 2011

An outlook of the literature concerning surface studies of polymer blends is given. Attention is focused on both theoretical and experimental aspects, with emphasis on the importance of sample preparation procedures.
Polyolefins ‐ poly(ethylene oxide) blends: Structure and properties
Authors: Kryszewski Marian , Morawiec Jerzy , Pluta Miroslaw , Uznański Pawel
Published: March 2011

Structure and properties of polyolefins‐poly(ethylene oxide) (PEO) blends were studied by combination of thermal analysis, light microscopy and fluorescence probe technique. Mixing and preparation conditions influence the calorimetric behavior, changing heat and temperature of melting and crystallinity degree of blended polymers. Values of the static mechanical parameters as well as flow characteristic parameters of the blends are lower for the higher PEO fraction in the samples. Fluorescence investigation of pyrene (changes in the vibrational fine structure) showed a nonhomogeneous distribution of the probe molecules between polyolefin and PEO environment. From these data the partition coefficient between polyolefin and PEO phase can be calculated and correlated with the crystallinity changes of the mixture composition.
Dynamic‐mechanical behaviour in the molten state of iPP/HOCP blends
Authors: Demma Giovanbattista , Acierno Domenico , Martuscelli Ezio
Published: March 2011

Dynamic‐mechanical data at various temperatures and for different blend compositions are presented for the system iPP/HOCP. The data, in all cases corresponding to the molten state, are relevant not only in view of the processing but especially because they allow some considerations on the blend structure. The data, looked at in different ways (namely the complex viscosity as a function both of frequency and temperature and in the form of Cole‐Cole plots), seem to indicate that the system is always in a single phase. This appears somehow in contrast to some microscopic observations recently reported in literature: the discrepancy may be, however, also due to changes in the miscibility due to the applied stress.
In situ polyolefin alloys
Authors: Cecchin Giuliano
Published: March 2011

through sequential copolymerization of appropriate ethylene‐propene mixtures into a preformed polypropene, or sligthly modified polypropene matrix (PP), it was possible to achieve and optimize some important property balances of the resulting multiphase copolymers, by finely tuning both the nature of the various phases and their volume and viscosity ratios. Thus, optimum stiffness/impact strength was achieved acting on the stereoregularity and molar mass distribution (MMD) of the polypropene matrix; transparency/impact strength by adjusting heterophase to matrix viscosity or density ratios and, finally, softness/transparency by generating large concentrations of highly amorphous ethylene‐propene bipolymers (EPM).
Blends of the β‐modification of polypropylene
Authors: Varga József , Schulek‐Tóth Ferenc , Mudra István
Published: March 2011

Preparation, crystallization and melting characteristics of blends of β‐nucleated isotactic polypropylene with different elastomers and polyethylenes were studied. Blends of β‐polypropylene can be prepared if the polymer additive is amorphous or has negligible α‐nucleating effect during the crystallization of polypropylene.
New polyamide ‐ based blends
Authors: Speroni Franco
Published: March 2011

Among polyamide based blends, PA/PP alloys show interesting technological properties due to low moisture absorption. A model class of PA6/PP homopolymer blends, compatibilized through the addition of PP‐g‐MA is described in the present work; the experimentally obtained morphologies are related to predictive equations for co‐continuity, at given rheological conditions. PP/compatibilizer ratio = 4/1 is found to impart an optimum level of phase dispersion. Moisture absorption, dimensional stability, mechanical properties and morphology are related with blend composition.
Specialties production by an innovative extrusion system
Authors: Addeo A. , Morandi C. , Vezzoli A.
Published: March 2011

The role of reactive extrusion (REX) appears more and more important in the future industry of polymeric materials. This process involves the design of special equipments and sofisticated process monitoring systems to allow complex chemical reactions and diversificated additivation at same time. In this paper, after a description of a specialized equipment designed for REX processing, some examples of experimental studies carried out using this line, are shortly addressed.
Controlled swelling of polymer brushes
Authors: Brochard‐Wyart F. , De Gennes P. G.
Published: March 2011

Very long chains with molecular weights up to 600000 can be grafted on a solid surface. We discuss here some specific features of these grafted systems: a) the climbing of a liquid along a vertical plane covered with long grafted polymer chains: because of a minute difference in chemical potential, the brushes can show color variations over an altitude ∼ 1 cm! b) swelling of brushes by elongated solvent molecules: this type of solvent can induce swelling in the isotropic phase, but when they become cooperatively ordered (nematic) we usually expect a collapse of the brush.
Brownian dynamics in strongly scattering porous media ‐ dynamic light scattering with single‐mode matching
Authors: Rička Jaroslav
Published: March 2011

Brownian motions in porous media represent a challenging problem not only from a theoretical but also from an experimental point of view. A very powerful technique for the measurement of Brownian motions is Dynamic Light Scattering (DLS). For our problem, however, the classic version of DLS is useless because the porous matrix scatters very strongly and the particles to be measured are completely masked. Sometimes it is possible to suppress the background scattering by matching the refractive indices of the matrix and the confined liquid, but this restricts the applicability to a handful of suitable model systems. We have introduced a new technique which overcomes this difficulty: The keyword issingle‐mode matchingand the idea is to select from the complicated random light field generated by the strongly scattering medium only a single mode so that the contribution from the matrix to the selected mode vanishes because of destructive interference. The first experimental results on the dynamics of latex particles in aqueous suspensions confined in a packing of glass beads are very promising. Their quantitative analysis demonstrates clearly the feasibility of measuring the diffusion coefficient within an opaque strongly scattering porous medium.
Static and dynamic light scattering of a random coil polymer in rodlike polymer solution
Authors: Jamil T. , Russo P. S. , Daly W. H. , Negulescu I.
Published: March 2011

We have studied ternary solutions of rodlike and random coil polymers in a common solvent. In these solutions, the rods scatter weakly, and almost all scattering comes from the coil component. From light scattering measurements, we gained information about the thermodynamic and hydrodynamic properties of the coil in rodlike polymer solutions.
Diffusion, rheology, and flow birefringence in block copolymer liquids near the ordering transition
Authors: Lodge T. P. , Xu X. , Jin X. , Dalvi M. C.
Published: March 2011

Measurements of the diffusion and relaxation of block copolymer chains near the order‐disorder transition (ODT) are reported. Forced Rayleigh scattering has been used to determine the diffusivities parallel and perpendicular to the lamellar planes, for poly(ethylene‐propylene)‐poly(ethylethylene) (PEP‐PEE) melts. The anisotropy is relatively weak (i.e., less than a factor of 4), but increases steadily as temperature is decreased. Rheology and flow birefringence have been employed to examine the conformational dynamics in block copolymer solutions. For PEP‐PEE in squalane, the stress‐optic relation is approximately valid, but the stress‐optic coefficient increases in the ordered state. The location of the ODT is consistent with the dilution approximation. For polystyrene‐polyisoprene (PS‐PI) diblock and triblock copolymers, the stress‐optic relation fails completely. There is evidence that the fluctuation regime (i.e., in the disordered state but near the ODT) may be considerably broader in block copolymer solutions than in melts. Furthermore, the onset of structure in the solution is accompanied by substantial form birefringence. In general, the optical signals are more complicated than the Theological ones, but also much more sensitive to small changes in temperature or concentration.
Dielectric studies on the dynamics of polymer chains in various environments
Authors: Kotaka Tadao , Adachi Keiichiro
Published: March 2011

Stockmayer's type‐A chain such as cis‐polyisoprene (PI) having dipole moments aligned parallel to the chain contour exhibits slow dielectric response, reflecting fluctuation of the end‐to‐end vector of the chain (dielectric normal modes). This article intends to review our own work on dielectric spectroscopy using PI as a probe for studying dynamics of large scale motion of the probe chain in binary blends with polybutadiene (PB) and in block copolymers with PB or with polystyrene. Through such studies we were able to see the features of polymer chain dynamics in various environments: Rouse‐Zimm‐like dynamics in overlapping‐but‐unentangled regimes, reptation with and without accompanying constraint release, behaviour of a subchain incorporated into block copolymers with miscible segments, and dynamics of polymer brushes in strongly segregating block copolymers in bulk and in solutions.
Synthesis and structure of metal complexes with organic polymers or inorganic supports
Authors: Ciardelli Francesco , Altomare Angelina , Conti Giuseppe , Arribas Guillermo , Mendez Bernardo , Ismayel Alida
Published: March 2011

Macromolecular ligands have been widely used in the past two decades with the objective of preparing structurally defined heterogeneous catalysts from soluble organometallic complexes. This activity has been largely reconsidered and focused on few specific systems. In this connection the present paper reviews recent data concerning the preparation of macromolecular metal complexes derived from transition metals which can produce active catalytic complexes for olefin polymerization and oligomerization and comparison is made about the suitability of both organic resins (crosslinked polystyrene) and inorganic materials (silica, alumina and zeolites).
Conduction in polymeric macrocyclic complexes
Authors: Hanack Michael
Published: March 2011

Bridged macrocyclic transition metal complexes using phthalocyanine and naphthalocyanine macrocycles e.g. [PcM(L)]n with M = Fe, Ru, Co and L = e.g. pyz, dib, tz, SCN−, CN− have been synthesized and their electrical properties studied in detail. Regardless of the bridging ligand stable semiconducting compounds are formed after doping with iodine. Some of these e.g. [PcM(tz)]n, M = Fe, Ru or e.g. [PcM(L)]n, M = Fe, Co; L = CN−, SCN− exhibit good semiconducting properties without additional doping. Substituted phthalocyanines (R4PcM where R = t‐Bu, Et, CH2OC12H25, C5H11‐C8H17) were also synthesized and were found to be more soluble in organic solvents. The characterization of the phthalocyanines prepared were carried out by IR, UV, 1H‐NMR and Mößbauer (Fe) spectroscopy.
Polymer‐supported pd(II) wacker‐type catalysts
Authors: Sherrington David C. , Tang Hui‐Gong
Published: March 2011

Seven polymer‐supported Pd(II) catalysts have been prepared employing polymers carrying nitrile (cyanomethyl) ligands. Five of these involve polybenzimidazole backbones, one a polystyrene skeleton and the last a polyacrylonitrile backbone. The supported complexes have been used with CuCl2 co‐catalyst to oxidise dec‐1‐ene primarily to the methylketone under normal Wacker oxidation conditions. In some instances the supported complexes are more active than the (CH3CN)2PdCl2 model. The most active species is a highly rigid ‐ cyanomethylated polybenzimidazole and at least some of these metal centres may be coordinatively unsaturated. This catalyst also displays remarkable thermo‐oxidative stability up to ∼400°C. The effect of solvent, temperature and co‐catalyst ratio have been examined. The polymer‐supported species remain very active at high temperature (∼120°C) and require addition of no hydrochloric acid to avoid irreversible precipitation of Pd(O) species. This is a complete contrast to homogeneous PdCl2 which is rapidly deactivated under similar conditions with copious Pd black formation. Pd(O) complexes immobilised on the polymer seem to be “site isolated” and unable to aggregate. Re‐oxidation therefore remains facile. The polymer‐supported species have been recycled seven times. An initial fall in activity levels after 3 cycles and thereafter remains essentially constant. Appreciable Pd leaching also occurs in the first reaction but is rapidly arrested. After ∼6 cycles Pd loss is only ∼1 ppm per cycle. Following use of CuCl2 co‐catalyst in the first cycle, no additional Cu(II) needs to be added, and sufficient co‐catalyst appears to be carried through with the isolated polymer‐supported Pd(II) species.

Starting with alk‐1‐enes isomerisation to the more thermodynamically stable internal alkenes is very much faster than oxidation. Indeed after only a short time no alk‐1‐ene is detectable e.g. by nuclear magnetic resonance analysis. Almost certainly, however, traces of the alk‐1‐ene do exist in equilibrium. Irrespective of whether the starting alkene is oct‐1‐ene, t‐oct‐2‐ene or t‐oct‐4‐ene the same three products are obtained: octan‐2‐one, ‐3‐one and ‐4‐one. In the case of oct‐1‐ene and t‐oct‐2‐ene the composition of the ketone product mixture is very similar, although with t‐oct‐4‐ene a significant increase in the proportion of the 4‐one is observed. The major product in all cases however in the 2‐one. The latter almost certainly arises from rapid oxidation of a small stationary concentration of alk‐1‐ene, with shift of the alkene equilibria maintaining the latter. Direct oxidation of the higher alkenes to the higher ketones occurs more slowly, but contrary to other reports in the literature this is significant.
Polymer‐bound bulky‐phosphite modified rhodium hydroformylation catalysts
Authors: van Leeuwen Piet W.N.M. , Jongsma Tjeerd , Challa Ger
Published: March 2011

Attachment of phosphites to styrene copolymers is described which are used as rhodium hydroformylation catalysts. The influence of the chain loading on the activity and complex formation of three types of copolymer‐bound rhodium hydroformylation catalysts in comparison with their low molecular weight analogues has been studied. The catalytic activity of the polystyrene‐bound system with the most bulky phosphite, the first system studied, is identical to that of the low molecular weight analogue. The catalysts show a high activity towards the hydroformylation of the otherwise unreactive cyclooctene. It was found that only one phosphite is coordinated to the rhodium complex in its active form. An equilibrium between this complex and an inactive complex without phosphite ligands prohibits its use in continuous flow reactors.

Secondly, as polymer support a perfectly random copolymer of styrene and less bulky 3,3′,5,5′‐tetra‐tert‐butylbiphenyl‐2,2′‐diyl p‐vinylphenylphosphite was used. The chain loading α of this copolymer with phosphite ligands has a large influence on the complex formation of the catalyst. With high chain loadings moderately active bis‐phosphite catalysts are formed. Low chain loadings give active, easily accessible, monophosphite complexes. The active species in the hydroformylation of sterically hindered alkenes is a mono‐phosphite rhodium complex. The activity of the copolymer‐bound catalyst towards the hydroformylation of cyclooctene is found to be as high as the activity of its low molecular weight analogue. For styrene, this polymer catalyst yields a slower catalyst than the low‐molecular weight analogue.

The third part demonstrates that silica‐grafted polymer‐bound phosphite modified rhodium complexes can be used in continuous flow reactors. The hydroformylation of styrene was carried out at moderate pressure (pCO/H2 = 3 MPa) and temperature (T = 100°C), yielding constant conversions over a period of at least ten days. These positive results were obtained in benzene as a solvent and for a ligand to rhodium ratio of only four.
Complexing polymer sorbents and metal polymer complex catalysts with specially designed structure of active centres
Authors: Efendiev A. A.
Published: March 2011

A new approach to a problem of preparation, regulation of properties and formation of three‐dimensional structure of complexing polymer sorbents and metal polymer complex catalysts with specially designed structure of active centres has been developed. The main principle is based on the use of “memory” of polymer composition and consists in prearrangement of macromolecules of initial complexing polymer or metal polymer complex catalyst to sorbing metal or hydrocarbon substrate followed by fixation of optimum for particular substrate conformation by intermolecular crosslinking. Using this principle a number of crosslinked complexing polymer sorbents and metal polymer complex catalysts containing phosphorylic, carboxylic, pyridine, amine and imine functional groups have been prepared. It has been shown that prearrangement leads to essential improvement of basic sorption and catalytic properties of the crosslinked complexing polymers ‐ sorption capacity, the rate of uptake, selectivity and catalytic activity.
Electrochemical quartz crystal microbalance studies of redox polymer films
Authors: Robert Hillman A. , Loveday David C. , Glidle Andrew , Vos Johannes G. , Clarke Alan P. , Kelly David , Bruckenstein Stanley
Published: March 2011

Electrochemical quartz crystal microbalance measurements are reported for redox switching of thin films of three macromolecule‐metal complexes: poly(vinylferrocene) (PVF), 10% osmium‐functionalized poly(vinylpyridine) (Os‐PVP), and 10% osmium functionalized poly(vinylpyridine‐co‐styrene) (Os‐PVP‐co‐PS). The data provide insight into the ion and solvent transfer processes associated with electron transfer between the electrode and the electroactive film. Four important parameters are identified: electrolyte composition, (co)polymer composition, prior film history and experimental time scale.
Electrochemistry and electrochromic properties of phenanthroline‐iron(II/III) complex films
Authors: Oyama Noboru , Kitagawa Mako , Inaba Hiroshi , Kawase Kazuya
Published: March 2011

New films of the iron complexes with bis((2‐hydroxyphenyl)methylaminosulfonyl)bathophenanthroline(HPBP) and bis((2‐aminophenyl)methylaminosulfonyl)bathophenanthroline(APBP) ligands are prepared on the electrode surfaces by electrochemical polymerization. The resulting film‐coated electrode shows a well‐defined reversible voltammogram corresponding to the redox reaction of the Fe(II/III) complexes and an electrochromic change from red(absorption maximum: 540 nm) to colorless. The response rate of the color change to a potential step was found to be correlated to the apparent diffusion coefficient(Dapp) for the homogeneous charge‐transport process within the film. The Dapp values estimated are (3‐4) × 10−9cm2s−1 for the [Fe(APBP)3] film and(1‐2) × 10−8cm2s−2 for the [Fe(HPBP)3] film, respectively, by potential‐step chronoamperometric and chronocoulometric methods. The result of electrochemical quartz crystal microbalance(EQCM) measurements4) and dependence of the formal potential of the metal complex of the Fe(II/III) redox couple with activity of the supporting electrolyte anion in NaClO4 aqueous solution showed that anion, cation, and solvent move simultaneously across the polymer film/solution interface during the redox reaction. A piezoelectric admittance measurement4) of the poly[Fe(APBP)3] coated quartz crystal electrode showed that the viscosity of the film is affected by the oxidation state of iron.
Theory of polymer melts and applications
Authors: Des Cloizeaux J.
Published: March 2011

The theory of polymer melts is founded on the process of double reptation for high masses and long times, and on simple Rouse relaxation for low maases and short times. In order to describe the intermediate region, these two different principles have to be combined, and we show how this can be done. However, pure reptation is modified under the influence of an effect which cannot be reduced to the Rouse elasticity of polymers, and this effect could be calculated by mode‐mode coupling.
Equilibrium and dynamical properties of gaussian stiff chain molecules
Authors: Winkler Roland G. , Harnau Ludger , Reineker Peter
Published: March 2011

We present a novel analytically tractable model for stiff chain molecules. The equilibrium distribution function of the chain is derived using the maximum‐entropy principle. For that purpose, we first formulate a discrete chain model, where the connections of the points and the restriction on bending are taken into account via constraints. We then perform the limit to a continuous chain and show that the mean‐square end‐to‐end distance and the radius of gyration of the continuous chain are identical with the same quantities of the Kratky‐Porod wormlike chain. The dynamics of our chain is investigated in dilute solution without hydrodynamic interactions. The linear dynamical equation is solved by a normal mode analysis. We discuss the dependence of the relaxation times on the single parameter of the model, the persistence length. For small persistence lengths we obtain the well known relaxation times of the Rouse model. In the stiff‐chain limit, we find the pure bending relaxation times and, in addition, the rotational relaxation time.
Dynamics of star polymers
Authors: Guenza Marina , Perico Angelo
Published: March 2011

Static and dynamic properties of star polymers in theta solutions are derived for semiflexible and the partially stretched (PS) arm models. The extension of the Optimized Rouse‐Zimm approach to describe the local dynamics (ORZLD) of star polymers is presented, together with some results for static and dynamic structure factors.
Molecular dynamics simulation studies of a complex fluid ‐solid interface ‐ the benzene‐alkane‐graphite system
Authors: Hentschke Reinhard , Kotelyanskii Michael J. , Winkler Roland G.
Published: March 2011

Interfaces between solid surfaces and solutions are of considerable scientific as well as technological interest, in particular in the context of the adsorption and the formation and organization of molecular films. The realistic modeling of such complex interfaces on the molecular scale is an important testing ground for simulation techniques. Here we focus on the benzene‐alkane‐graphite interface as an example of the above class of systems, including surface induced segregation, adsorption, and structural aspects of the graphite‐solution interface.
Polymer crystallization: Simulation with entropic barrier model and application to specific polymers
Authors: Goldbeck‐Wood Gerhard
Published: March 2011

The growth of polymer single crystals has been simulated on the basis of a simple two‐dimensional ‘entropic barrier’ model. The chain is described by a sequence of growth units. Their additions and removals are determined by rate constants obeying detailed balance. The crystallization is then simulated by a kinetic Monte Carlo algorithm. An application of the model to specific crystallizable polymers (polyethylene, isotactic polystyrene, isotactic polypropylene, polyhydroxybuterate and polypivalolactone) is presented. Input parameter values for the model are derived from the respective surface free energies, bulk enthalpies, melting points and crystallographic repeat lengths. The only free parameter is the length of a polymer growth unit. This is set to half the lamellar crystal thickness at large undercooling. The lamellar thicknesses calculated on this basis are in good agreement with experimental data. An analysis of the growth unit lengths of the different polymers indicates a scaling with the chain persistence length in the melt.
Models for cracking of polymer coatings
Authors: Sokolov Igor M. , Morgenstern Olaf , Blumen Alexander
Published: March 2011

We investigate the dynamics of cracking of a brittle coating covering an elastically stretched substrate. We consider here a scalar model (an electrical analogue) in order to describe fractures in thin and in thick films. The model captures the essential features of the fragmentation of coatings and allows us to classify different temporal regimes in the cracking process and to obtain several basic patterns of the cracks' morphology.
Prediction of polymer miscibility from molecular mechanics calculations
Authors: Gorella Boris , Tiller Andrew R.
Published: March 2011

A new computational method is presented for the rapid estimation of polymer miscibility. The algorithm (coined FLEXIBLEND) uses molecular mechanics calculations on a pair of polymer segments and takes into account the effects of local chain flexibility to estimate heats of mixing. This paper shows miscibility predictions in agreement with experiment for blends of poly(ethyleneoxide) (PEO) with isotactic poly(propylene) (PP) as an immiscible system and of PEO with poly(acrylic acid) (PAA) as a miscible system.
Simulation study of poly(γ‐benzyl‐l‐glutamate) in dimethylformamide
Authors: Helfrich Jürgen , Hentschke Reinhard , Apel Ute
Published: March 2011

We perform atomistic Molecular Dynamics simulations of Poly(γ‐Benzyl‐L‐Glutamate) (PBLG) in Dimethylformamide (DMF) to study the structure and some dynamic aspects of the complex side chain ‐ solvent interface. In addition, we investigate the elastic behavior of PBLG with the emphasis on the determination of the persistence length.