bluuebunny/crossref_metadata_2025 huggingface dataset:
Rubber elasticity of branched polyethylenes
Authors: Klein P. G. , Brereton M. G. , Rasburn J. , Ward I. M.
Published: March 2011

Two grades of ethylene/1‐hexene copolymer, containing about 0.4 and 1.3 butyl branches per 1000 carbons, were subjected to electron beam irradiation in vacuum and in an acetylene atmosphere. The resulting networks were characterized by gel fraction determination and melt elasticity behaviour. The rubber elastic force‐extension data were analysed in terms of the Edwards‐Vilgis slip‐link model. This theory provided good fits to the experimental data, and the calculated parameters agreed well with the gel fraction determinations. The results indicate that an increase in branch concentration causes an increased susceptibility to chain scission.

Irradiation in acetylene is shown to enhance greatly the crosslinking process, without affecting the chain scission, leading to a more perfect network.
Mechanochemical energy conversion of neutral polymer gels
Authors: Horkay Ferenc , Zrinyi Miklós
Published: March 2011

Mechanochemical energy conversion exhibited by water‐swollen poly(vinyl alcohol) gels has been studied. The effective mechanical work produced as well as the chemical energy converted were measured simultaneously. It is shown theoretically and experimentally that the mechanical work developed during the swelling of the mechanochemical system increases with increase of the external load (m), the degree of cross‐linking (DC) and the deswelling ratio (ϕ/ϕe, i.e. the ratio of the volume fraction of network polymer (ϕ) to that of the same gel in equilibrium with pure diluent (ϕe)). The chemical energy converted was found to be practically independent of m. The efficiency of energy conversion increased with increase of m and DC, and significantly decreased with increase of ϕ/ϕe. Comparison is made between theoretical predictions and experimental findings.
Mechanism and kinetics of the radical polymerization of acrylamide in inverse micelles
Authors: Candau Françoise
Published: March 2011

A kinetic study of the photoinitiated polymerization of acrylamide in oil/AOT/H2O reverse micelles has been investigated. Determinations of the dependence of the rates of polymerization and the molecular weights of the polymers on initiator and monomer concentrations, as well as the relative light intensity and the identity of the oil employed were performed. Rates of polymerization were measured by dilatometry, and polymer molecular weights were determined by viscometry. The polymerization was shown to be first order in monomer concentration, and the order of the termination step of the polymerization depended strongly upon the oil employed. When the oil was benzene, termination occurred by a biradical process. When benzene was replaced by toluene, a monoradical termination was shown to occur, suggesting that a degradative chain transfer to toluene is occurring in this case. The similarities and differences of polymerization in conventional emulsions and in micelles are discussed on the basis of these results.
Synthesis of block copolymers by heterogeneously initiated emulsion polymerization
Authors: Chrástová V. , Citovický P. , Pristačová J.
Published: March 2011

The contribution refers to the possibility of using emulsion polymerization of styrene, initiated by a heterogeneous initiator Chydroperoxide of isotactic powdered polypropylene) in the presence of a complex type activator, for the synthesis of block copolymers. Vinylmonomers with various water‐solutibility, i.e. methyl methacrylate (MMA), acrylonitrile (AN) and maleic anhydride (MA), were utilized as comonomers of styrene. It was found that at the used conditions, the composition of block copolymers PS‐b‐P(S/AN) and PS‐b‐PCS/MA) can be varied by the time of polymerization of the first or second comonomer. The block copolymers were characterized by their molecular weight, and their thermal stability was also investigated.
Polymer networks via cationic ring‐opening polymerization
Authors: Goethals Eric J. , van Meirvenne Dirk , Trossaert Geert , Deveux Robert
Published: March 2011

Three methods for the formation of polymer networks from bifunctionally growing polymers obtained by cationic ring‐opening polymerization are described. The first method is based on the irreversible inter‐molecular termination reaction of thietane polymerizations. Starting from bifunctionally living poly(THF) a new kind of polymer structure consisting of ABA block copolymers with cross‐linked A‐segments is obtained. The second method is the direct coupling of active species with primary amines or ammonia. The third method consists in transformation of the living end groups of poly(THF) into triethoxysilane end groups, followed by cross‐linking by addition of water and a trace of acid.
Catalyzed silicon‐mediated living polymerizations, structure control, catalyst design and mechanisms
Authors: Sogah D. Y. , Hertler W. R. , Dicker I. B. , Depra P. A. , Butera J. R.
Published: March 2011

Group transfer polymerization (GTP) and the related Aldol‐GTP are new types of living polymerization mediated by silicon for precise control of polymer structure. The two processes are regenerative in that the reactions are accompanied by transfer of silyl group from living end to the incoming monomer and vice versa to produce a reactive functional group as the living end. The reaction can be carried out on solid supports, such as crosslinked polystyrene. Even though the reactions are normally catalyzed, they can be carried out at high pressures without the use of any catalyst. They operate above room temperature, thus enabling one to control molecular weight, polydispersity and monomer sequence under industrially significant conditions. The scope of catalysis is broadened to cover oxyanions.
Recent developments in living carbocationic polymerization of alkenes
Authors: Kennedy Joseph P.
Published: March 2011

The recent discovery of living cationic polymerization of alkenes has been followed up in three areas: 1) Demonstration of the validity of the DPn = [Mo]/[Io] relationship and the synthesis of high molecular weight polyisobutylenes Mn_>100 000) of narrow molecular weight distribution (Mw/Mn ≈︁1.1) 2) Discovery of electrophilic quenching and the use of this method for the preparation of allyl‐telechelic polyisobutylenes by quenching with trimethylallylsilane and 3) Synthesis of novel linear and three‐arm star radial thermoplastic elastomers comprising rubbery polyisobutylene central sequences connected to glassy polystyrene or a polystyrene derivative (i.e., p‐methylstyrene, p‐tert‐butylstyrene, indene) outer sequences. Some physical‐mechanical properties of these materials have been investigated.
Design and initiators of living cationic polymerization of vinyl monomers
Authors: Sawamoto Mitsuo , Higashimura Toshinobu
Published: March 2011

This paper discusses recent developments in living cationic polymerization of vinyl monomers, specifically focusing on (a) new initiating systems, (b) kinetics and mechanism, and (c) controlled polymer synthesis. The new initiating systems were based on nucleophilic stabilization of the growing carbocations, either by counteranions (as in phosphate/ZnI2 and Me3SiI/ZnI2 systems) or by added Lewis bases (as 2,6‐dimethylpyridine for EtAlCl2). The kinetic study included the determination of the lifetime of living cationic polymers. The controlled polymer synthesis by living cationic processes led to not only end‐ and pendant‐functionalized polymers of narrow molecular weight distributions but also star‐shaped polymers and sequence‐regulated vinyl ether oligomers with functional groups.
Kinetics of polymerization by activated monomer mechanism
Authors: Biedron Tadeusz , Szymanski Ryszard , Kubisa Przemyslaw , Penczek Stanislaw
Published: March 2011

Polymerization of cyclic ethers by activated monomer mechanism involves consecutive additions of protonated monomer molecules to the growing macromolecules fitted with hydroxyl groups at their ends. For oxirane itself and symmetrically substituted oxiranes there is only one kind of hydroxyl groups and one, unique way of ring‐opening. Unsymmetrically substituted oxiranes provide however two sites of attack and two different hydroxyls, resulting from these ring‐openings.

Kinetics of polymerization of epichlorohydrin (chloromethyloxirane) has been studied and all four rate constants determined, namely rate constants of the primary and secondary alcoholate chain ends with a protonated monomer, opening in result of the attack on substituted or unsubstituted carbon atom. These rate constants are (in mol−1·1·s−1 at 25°C, in CH2Cl2 solvent): k11 = 0.055, k12 = = 0.41, k22 = 0.135, and k21 = 0.0011 (e.g. k12 is the rate of reaction of the primary alcohol producing the secondary alcohol). Thus, polymerization proceeds almost exclusively on the secondary alcoholate groups, reproducing themselves (k22).
Anionic and pseudoanionic polymerization of lactones ‐ a comparison
Authors: Kricheldorf Hans R. , Kreiser‐Saunders Ingrid , Scharnagl Nico
Published: March 2011

Polymerization via anionic mechanisms or insertion mechanisms (pseudoanionic mechanisms) are compared for β‐lactones and L‐lactide. The following aspects are discussed: initiation and deprotonation of β‐lactones, back‐biting degradation, stereosequences of poly(β‐D,L‐butyrolactone), racemization of L‐lactide, systematic variation of endgroups including synthesis of macromers.
Eval membranes for blood dialysis
Authors: Chen Leo‐Wang , Young Tai Horng
Published: March 2011

Both dry‐ and wet‐process were employed for preparing membrane of ethylene‐vinylalcohol copolymer (EVAL) for blood dialysis.

Asymmetric and symmetric, dense or porous membranes were prepared by the dry‐process. The relationship between the structure of membranes and the experimental variables is explained by using a solubility curve model. This model predicts the membrane structure successfully under various conditions, including the change of temperature of the environment, the solvent system and the temperature of polymer solution. For wet‐processes, the casting solutions were coagulated in a precipitation bath (water). Three different structures were obtained: finger type, sponge type and particle‐bonded type. The cloud point experiment and the polymer segment motion help to understand and control the membrane structure. Some properties of the EVAL membrane for blood dialysis are shown. It is comparable with or better than the commercialized one. This study may prove useful in determing the controlling parameters for the preparation of membranes from other polymers.
Synthesis and evaluation of polyamine graft and block copolymers as novel biomaterials for cell separation
Authors: Tsuruta Teiji
Published: March 2011

Graft copolymer (HA) composed of 2‐hydroxyethyl methacrylate (HEMA) and a polyamine exhibits unique biospecific behavior at the interface with living cells. In the present paper, the writer will discuss on four topics : (i) effective separation of rat lymphocyte subpopulations by using HA copolymer; (ii) surface analysis of HA copolymers by ESCA and streaming potential measurements; (iii) a hybrid field flow fractionation/adhesion chromatography technique; and (iv) specific cellular recognition of poly(HEMA)‐graft‐quaternized polyamine copolymer (HQA)
Proton spin diffusion as a tool for characterizing polymer blends
Authors: VanderHart D. L.
Published: March 2011

Proton spin diffusion studies for characterizing minimum domain dimensions have been carried out on three blends: a 40/60 blend of nylon 6,6 with the aromatic rigid rod polymer poly(benzo[a,d]dithiazol‐2,6‐diyl‐1,4‐phenylene), PBZT, a 47/53 blend of an amorphous nylon with PBZT, and a 50/50 blend of a polyetherimide (PEI) and a polybenzimidazole (PBI). Polarization gradients necessary for these experiments were generated using both chemical shift differences (via multiple pulse techniques) and linewidth differences. Polarization readout techniques included proton lineshape deconvolution, multiple pulse proton lineshapes and 13C CPMAS spectra utilizing short CP times. The two nylon/PBZT blends are expected to phase separate from thermodynamic arguments; however, kinetic considerations, more than thermodynamics, determine domain size. In the 40/60 blend, the minimum domain dimensions of each of the nylon and the PBZT phases were about 4 nm with some scattered larger crystals of nylon. In the 47/53 blend, mixing in some regions indicated domain dimensions similar to the 40/60 blend. In contrast to the 40/60 blend, however, the 47/53 blend was still far from internal spin polarization equilibrium after spin diffusion times of 140 ms. The implication is that the sample‐average composition is not found over dimensions like 40 nm; the problem is that the possible morphological explanations are manifold. By investigating the proton rotating frame relaxation, T1p, the possibility that some of the PBZT domains are isolated from the nylon, in a spin diffusion sense, was eliminated. It is more likely that about half of the nylon protons are isolated by spin diffusion from the PBZT protons on a 140 ms timescale. The PEI/PBI blend is a compatible blend of two aromatic polymers where mixing on a molecular scale is expected. We were interested in a measurement of the lower limit of domain size using proton spin diffusion. This lower limit turned out to be about 2.5 nm based on low temperature T1p measurements as opposed to room temperature multiple pulse methods. The latter measurements monitored the disappearance of a polarization gradient between the PEI methyl protons and all the remaining protons. The superiority of the T1p measurements over the multiple pulse method for establishing the smaller minimum domain dimension is not a general result and reasons are discussed. Finally, some general remarks about characterizing polymer blends by solid state NMR, particularly blends which have undergone spinodal phase separation, are included.
1H spin‐lattice relaxation and observation of interfacial material in solid polyethylenes
Authors: Packer K. J. , Poplett I.J.F. , Taylor M. J. , Vickers M. E. , Whittaker A. K. , Williams K.P.J.
Published: March 2011

The 1H NMR laboratory‐ and rotating‐frame (LF,RF) spin‐lattice relaxation (SLR) behaviour in solid polyethylenes is reviewed in light of the two region spin diffusion coupled model. Highly crystalline high‐density materials show single T1 values indicative of the fast diffusion limit whilst RFSLR is close to the slow diffusion limit, allowing direct determination of the dimensions of the crystalline and disordered regions. The LFSLR and RFSLR of the HDPE's suggest the existence of an interfacial material which the SLR behaviour includes as part of the crystalline region in contrast to XRD and DSC. 13C CPMAS measurements of 1H RFSLR in a LLDPE provide an additional insight into this problem. The 1H RFSLR is best represented by a superposition of two exponentials, measured by either 1H or 13C NMR. The 1H RFSLR, measured at different chemical shifts in the 13C NMR spectrum, provides direct evidence of the interfacial material. The possible use of spin‐locking at angles other than 90° in the rotating frame to scale the spin diffusion rates is reviewed and its possible utility for LLDPE materials explored.
NMR investigations of polymer electrets
Authors: Geschke Dieter , Holstein Peter
Published: March 2011

1H NMR investigations were performed on thin films of poly(vinylidene fluoride) (PVDF) and polyamide 11 (PA 11). The variation of the angle between the static magnetic Bo‐field and preferred directions given by drawing and poling leads to characteristic dependences of T20ff, which can be discussed in terms of Legendre polynomials of the orientational distribution functions of crystallographic c‐ and b‐axis. A good c‐axis alignment can be realized by uniaxial drawing. The tendency for b‐axis to orient towards the direction of the applied electric field via the orientation of the electric dipoles is evident. The b‐axis alignment can be “switched” periodically.
Relaxation spectrometry in solid polymers based on NMR and EPR measurements
Authors: Kashiwabara Hisatsugu , Shimada Shigetaka , Hori Yasurō
Published: March 2011

Wide distribution of relaxation times is taken into consideration in determination of the activation energy of the molecular motion associated with the motional narrowings of line widths of magnetic resonance spectra. The molecular motion of rotational vibration around the chain axis of polyethylene in urea‐polyethylene inclusion complex is examined. Relaxation spectra can be obtained from the data of the motional narrowings of EPR and NMR by assuming the activation energy as a parameter. Also, the representative relaxation times corresponding to EPR and NMR observations can be estimated. These relaxation times give us an activation energy since EPR and NMR observations correspond to different time constants of observations. The activation energy estimated from the data of the representative correlation times is identical with the activation energy obtained as a parameter in determination of the identical relaxation spectrum from the data of motional narrowings of EPR and NMR observations.
The measurement of diffusion and flow in polymer solutions using dynamic NMR microscopy
Authors: Xia Y , Callaghan P T
Published: March 2011

The new method of dynamic NMR microscopy has been used to obtain velocity and diffusion maps for polymer solutions in capillary flow. In particular we observe power law shear‐thinning behaviour in poly(ethylene oxide) (PEO) solutions in the semi‐dilute regime but without slip at the walls. Some evidence is apparent for enhanced solvent diffusion along the shear axis in region of high shear.
ESR and ESE studies on polymer semiconductors of weakly doped poly(tetrathiafulvalene)
Authors: Roth H.‐Klaus , Brunner Winfried , Völkel Georg , Schrödner Mario , Gruber Harald
Published: March 2011

In the studied poly(tetrathiafulvalenes), PTTF, the TTF units are linked via phenyl groups or via tetrahydroanthracene bridges. The PTTF are doped with oxygen and with iodine respectively. The electrical conductivity strongly depends on temperature as it is typical of semiconducting materials.

The existence of various types of paramagnetic centres is confirmed by ESR saturation experiments, by spectra simulation and by electron spin echo (ESE) measurements in the temperature region of 2 K to 400 K. At room temperature the doped PTTF have a dc conductivity between 10−9 Scm−1 and 10−4 Scm−1.

Relations between the concentration of various radicals and the electrical conductivity of the polymers are discussed by means of a model based on mobile and immobile radicals, polarons and bipolarons. There are experimental indications for temperature‐dependent formation and break‐up of bipolarons which are discussed in the paper.
Investigations of anomalous photo‐current in poly(n‐vinylcarbazole)/trinitrofluorenone in regarding dipole relaxation
Authors: Wünsche Peter , Althausen Dietrich
Published: March 2011

Measurements were carried out of the change of polarity of photo‐current after a laser flash on poly(N‐vinylcarbazole) with trinitrofluorenone (PVK/TNF). This experimental results could be interpreted by taking into consideration dipol‐relaxations. A model for estimation is presented.
Vibrational spectra of polyacetylenes
Authors: Dellepiane Giovanna , Piaggio Paolo , Cuniberti Carla , Fuso Silvano , Musso Gianfranco , Rui Marina , Tubino Riccardo
Published: March 2011

A considerable amount of information about optical and electronic properties of polyacetylenes has been obtained during the last decade from vibrational spectroscopy. In this lecture several basic points not yet fully understood will be discussed and a new method for evaluating the vibrational density of states for random defects will be presented.
Electrical properties of poly(tetrathiafulvalenes)
Authors: Gruber Harald , Roth Hans‐Klaus , Patzsch Jörg , Fanghänel Egon
Published: March 2011

Results of conductivity measurements on undoped and iodine or bromine doped poly(tetrathiafulvalenes) are reported. At higher temperatures the temperature dependence of the d.c. conductivity can be best described by σd.c. = °o. exp(T/To)1/4, typical for variable range hopping. The a.c. conductivity follows the general law °(ω) ∼ ω2 for frequencies higher than a critical frequency. A description of the frequency dependent conductivity is given by the extended pair approximation (EPA). At lower temperatures a deviation from linearity of the function in σ versus T−1/4 is observed.
Conditions for the formation of superconductive polymers and possibilities for their realization
Authors: Grigorov L. N.
Published: March 2011

General principles of the creation of superconductivity at the polymers are considered. It is shown that high temperature superconductivity may be produced only at really one‐dimensional conducting materials. It is also shown that conjugated polymers cannot have onedimensional conductivity. The new class of nonconjugated polar elastomers is proposed as a perspective one for the creation of high temperature superconductive structures–superpolarons–which appear as a result of internal selfionization of the polymer matrix and a consequent selforganization of free polarons. The practical methods of the formation of superpolarons are shown for the films of oxidized atactice polypropylene. Evidences are given which show the existence of superconductive structures in oxidized polypropylene at room temperature.
Structure and electronic properties of ladder polymers. A new class of conducting polymers
Authors: Wuckel L. , Lehmann G.
Published: March 2011

Theoretical calculations have been applied to design novel synthetic polymers which show metallic conductivity without doping. Some selected highly conjugated structures were calculated using a HUCKELMO method extended by introducing elastic sigma bonds. A group of highly conjugated aromatic ladder polymers is promising in this context. Another interesting group consists of laddered heteroaromatic structures in which carbon atoms are replaced by nitrogen.

Ionization potentials, electron affinities, band widths, band gaps as well as oxidation and reduction potentials were calculated. Small, band gaps were obtained for polyacene, polyperinaphthalene and polypyridinopyridine. The values are in good aggreement with that obtained on the basis of the VEH method. This paper reports also some efforts to prepare polyacene, polyperinaphthalene and polypyridinopyridine, and to investigate their electronic properties.

Concerning their electrochemical properties high specific capacities and good electrochemical stability has been found in aprotic lithium cells.
Dynamics of uv excimer laser ablation of pmma, caused by mechanical stresses theory and experiment
Authors: Kitai M. S. , Popkov V. L. , Semchishen V. A.
Published: March 2011

A quantitative model of PMMA ablation was developed. Photochemical reactions, heating of the polymer and mechanical stresses were taken into consideration. The increasing of the optical absorption during the photochemical reaction caused by ArF laser radiation was investigated. The developed model allowed to evaluate the ablation parameters.
Structuring of polymer blends in simple shear flow
Authors: Lyngaae‐Jørgensen J. , Valenza A.
Published: March 2011

A simplified model for the formation of steady state structure of discrete domains in polymer blends is established for simple shear flow. It is assumed that the domain size distribution, which results from an equilibrium between breakup processes and coalescence processes, may be divided in small and stable spherical domains and large and unstable ellipsoidal domains. Based on simplified rate balances and an expression for domain deformation rate the volume fraction of large domains and the large and small semiaxes of the ellipsoids are expressed as functions of volume fraction and shear rate/shear stress. The ability of the model to simulate actual behaviour is tested against quantitative data for polystyrene/poly(methyl methacrylate) blends. It is concluded that the Taylor type behaviour is approached at low volume fraction and low shear stress. The aspect ratio, P, shows a maximum in a plot against shear stress with volume fraction as discrete variable. For certain concentrations P seems to approach infinity thus forming infinitely long fibers.
Interpenetrating polymer networks, the state of the art
Authors: Sperling L. H. , Fay J. J. , Murphy C. J. , Thomas D. A.
Published: March 2011

Interpenetrating polymer networks are combinations of two crosslinked polymers. Often, they exhibit dual phase continuity, meaning that both phases extend continuously throughout the sample. Recent research on IPNs has shown that both nucleation and spinodal decomposition mechanisms are important in the kinetics of phase separation.

If the polymers are almost miscible, a microheterogeneous morphology will develop. Under these conditions, the glass transition of the IPN may be very broad, extending the range between the glass transition of the two homopolymers. Such materials are useful for sound and vibration damping. The loss and storage modulus, and tan δ behavior of polymers and IPNs in the glass transition region were evaluated on a quantitative basis, in order to characterize their damping behavior better. Corrections for background in dynamic mechanical spectroscopy studies will be discussed. The storage modulus of polystyrene at 25°C was selected as a standard. The development of a group contribution analysis of the integral area under the linear loss modulus‐temperature curves, the loss area, LA, is reviewed, and applied to a number of acrylic, styrenic, and vinyl statistical copolymers and IPNs. Each moiety in a polymer is shown to contribute to LA on a simple, additive basis.

New research emphasizes the role of morphology and phase continuity in determining LA. The system cross‐poly(vinyl methyl ether)‐inter‐cross‐polystyrene was selected, because its phase diagram in the blend state is well known, and it has become both a model and interesting system to investigate. Midrange IPN compositions exist as two phases at room temperature, as illustrated by dynamic mechanical spectroscopy.
Reactive processing and blending of polymers making use of mechanoradicals
Authors: Geuskens Georges
Published: March 2011

The grafting of various vinyl monomers on polyethylene and on ethylene‐propylene copolymers has been initiated by mechanoradicals in an internal mixer. This is possible if the polymer has been slightly cross‐linked by γ‐radiation before processing or is dynamically cross‐linked by peroxides during processing. Some properties such as adhesion to metals or impact resistance of blends containing the modified polymers are improved.
Controllable specific interactions and miscibility in polymer blends, 2. A brief description of the main results
Authors: Jiang Ming , Cao Xianyi , Chen Wenjie , Xiao Hong , Jin Xiaoling , Yu Tongyin
Published: March 2011

In this paper, we briefly report the main results of our work on the effect of introducing specific interaction on the miscibility of otherwise immiscible polymer blends. A strong proton‐donating unit (CF3)2(OH)C‐ was incorporated into polystyrene (PS(OH)). A series of blends of PS(OH) with one of polyacrylates such as PBA, PMMA, PEMA and PBMA was studied. The infrared spectra of the blends present convincing evidence of the formation of hydrogen bonding. The frequency shift of the OH stretching band due to H‐bonding is independent of the structure and composition of the hydroxyl‐containing polymers, but clearly dependent on those of the counterpolymers. Both excimer and nonradiative energy transfer (NRET) fluorescence techniques have proved effective for monitoring the variation of the degree of molecular interpenetration with the density and strength of the hydrogen bonds in the blends. TEM observations reveal clear and regular variation in the morphology of the blends with the content of hydroxyl‐containing groups. The morphological features of this kind of blends are almost controllable since the structure and/or amount of the introduced groups forming hydrogen bonding are readily adjusted in chemistry. NRET and viscosity measurements of solutions of polyacrylate and PS(OH) with relatively high hydroxyl contents in toluene provide evidence of the intermolecular complexation. In addition, the effect of introducing simultaneously crosslinking and intermolecular hydrogen bonding into blends of PS and PBA on miscibility was studied. It is concluded that single phase IPN can be prepared, but much higher content of the proton donor is needed in comparison with the blends of the corresponding linear polymers. The interlocking structure of the networks appears unfavourable to forming miscible IPN.
Processing and properties of blends with liquid crystal polymers
Authors: La Mantia Francesco Paolo , Valenza Antonino
Published: March 2011

Experimental data on the processing behavior and on the rheological and mechanical properties of blends with a liquid crystal polymer as one component are presented. The blends with low amounts of LCP show easier processability and lower viscosity than the thermoplastic matrix. The elastic modulus is also improved. The reduction of viscosity has been attributed to the lower pressure entry, due to the formation of fibrils and to the immiscibility of the two phases.
Phase behaviour of ordered polymer solutions
Authors: Koningsveld R. , Stockmayer W. H. , Nies E.
Published: March 2011

Rules for equilibrium phase behaviour, laid down long ago on the basis of the two laws of thermodynamics, appear to be valid also for many polymer systems in which aggregates of various topology occur. The phase rule offers a useful tool for the construction and understanding of phase diagrams for systems in which order of some kind is prevalent in certain ranges in the diagram. ‘Double sickle’ type phase diagrams, found for surfactant solutions, microemulsions as well as block‐copolymer solutions can be traced back to the considerable loss of translational entropy which accompanies aggregation.
Phase separation in the poly (γ‐benzyl‐α, l‐glutamate)/benzyl alcohol system
Authors: Horton J. C. , Donald A. M.
Published: March 2011

We describe phase separations seen in the poly (γ‐benzyl α, L‐glutamate) (PBLG)/benzyl alcohol (BA) system. At temperatures below about 60°C, this system gels. Possible explanations of the system's rigidity include both crystallisation and spinodal decomposition. Recent work on atactic polystyrene (a‐PS) gels has suggested these are the result of a phase separation arrested by vitrification. An analogy between a‐PS and PBLG gels is suggested whereby crystallisation (in the latter) plays the rǒle of vitrification in the former.
Ligand‐exchange chemistry of Cr13‐polyacrylamide gels
Authors: Burrafato Giovanni , Albonico Paola , Bucci Silvia , Lockhart Thomas P.
Published: March 2011

Evidence that ligand‐induced de‐gelation of Cr(+3)/polyacrylamide (PAAm) gels involves simple extraction of Cr(+3) from the gel matrix has been obtained from rheological studies. Kinetic experiments provide evidence that de‐gelation involves dissociative ligand exchange at Cr(+3). On the basis of de‐gelation results acetate is suggested to be a poor thermodynamic model for the bonding of PAAm to Cr(+3) and it is hypothesized that Cr(+3)/PAAm complexation may involve bonding to both a polymer carboxylate and a neighboring amide group.
The structure of poly(ethylene oxide)‐poly(dimethyl‐siloxane) triblock copolymers in solution
Authors: Maassen H.‐P. , Yang J. L. , Wegner G.
Published: March 2011

A series of triblock copolymers consisting of oligomeric segments of poly(ethylene oxide)(PEO) and poly(dimethylsiloxane) (PDMS) were synthesized. These amphiphilic polymers have the general structure (PEO)n‐Z‐(PDMS)m‐Z‐(PEO)n or inversely (PDMS)m‐Z–(PEO)n‐Z‐(PDMS)m where “Z” is the group linking the chains of different polarity. n and m varied in the range m, n < 77. These polymers spontaneously form lyotropic mesphases if mixed with water. The phasediagrams and symmetry of the phases were determined. Moreover, photoreactive groups were attached at exactly and only the positions “Z” of the block copolymers. When photocrosslinking was induced in a particular lyotropic mesophase, the arrangement of the molecules in this phase structure was fixed. Although the phase structure collapsed when the systems were freed from water, the structure returned on reswelling. Some rules concerning the tendency of such molecules to self‐organize as a function of the molecular structures are obtained.
Colloid structure in polyethylene‐wax/n‐paraffin mixtures
Authors: Sawodny Michael , Asbach Gerd‐Ingo , Kilian Hanns‐Georg
Published: March 2011

The spherulite structure and its genesis in WAX PE130 are discussed on the basis of DSC, X‐ray small‐angle and raster‐electron‐microscopical measurements. Modifications of this superstructure in the presence of a low‐molecular‐weight solvent are shown. The role of thermodynamics and kinetics is reflected. Conclusions are drawn which imply general aspects that governs the growth of spherulites.
Ion complexation of biopolymers: Macromolecular structure and viscoelastic properties of gels
Authors: Axelos M. A. V.
Published: March 2011

The effect of charge density and solvent conditions have been explored on sodium pectinate–calcium system undergoing gelation. Viscosity and shear modulus were determined respectively before and after the transition. More than 55% of sugar residues need to be charged to build a network. The amount of calcium required increases dramatically with the decrease of pH and ionic strength. Pectins in salt–free solutions are rapidly connected by calcium ions but the crosslink density remains lower than in NaCl‐rich solutions. Small angle X‐ray scattering indicates that the junction zones may be viewed as rod‐like cylinders whose cross–section radius increases from 3 to 6 and 8 Å when the ratio R = 2 (Ca2+)/(COO−) changes from 0 to 0.5 and 0.75.
Monte Carlo calculation of a partial reaction in radical cross‐linking of 1,4‐polybutadiene
Authors: Martl Michael G. , Saf Robert , Hummel Klaus
Published: March 2011

In simulation of radical cross‐linking of 1,4‐polybutadiene the formation of cross‐links is assumed to occur in the following steps: Formation of radicals from a low‐molecular‐weight compound, hydrogen abstraction from the polymer chain resulting in polymer radicals and finally mutual substitution of two polymer chains. The reaction is complicated by a coupled partial double‐bond shift. The frequency distribution of the fraction of C atoms between cross‐links is investigated as a function of the probability of double‐bond shift and the degree of substitution. This distribution depends significantly on the extent of the double‐bond shift. The discussion of network structures considering only physical network theories is therefore insufficient and should also include chemical aspects.
Enhancement of inhomogeneities in gels upon swelling and stretching
Authors: Bastide Jacques , Mendes Eduardo , Boué François , Buzier Martine , Lindner Peter
Published: March 2011

In this paper, it is shown how a percolation process can be used to describe the inhomogeneities of polymer concentration, appearing in gels prepared by random crosslinking of a semi‐dilute solution, and how they are modified by swelling or stretching of the network. Neutron scattering experimental data are compared to the predictions of this model in the isotropic and anisotropic cases. A good agreement is found. In particular, “abnormal” butterfly patterns in the iso‐intensity curves have been detected, as expected from the model.
Chain orientation in deformed networks via NMR
Authors: Poon Chi‐Duen , Samulski Edward T. , Nakatani Alan I.
Published: March 2011

We quantitatively simulate the deuterium NMR linshapes that result when labelled poly(dimethyl siloxane)‐d6 networks are uniaxially strained. The inferred microscopic reorientational processes that the chain segments exercise in (deformed) networks are indicative of dynamic heterogeneity wherein different parts of the network average the residual quadrupolar interaction to different degrees. The higher the molecular weight between crosslinks, the larger the fraction of slow reorienting species suggesting that chain disinterpersion may be the rate‐limiting contribution to segmental motion in long chains. Our depiction of the network at ambient temperature is that of a liquid wherein motionally distinct segmental domains are characterized by different rotational correlation times. However, under uniaxial extention the fluid network is similar to an anisotropic liquid having macroscopically homogeneous (nematic‐like) segmental orientational order that is characterized by a single order parameter. Order parameters extracted from the NMR simulation are discussed in terms of classical descriptions of how macroscopic strain induces microscopic orientational order in Gaussian networks.
Structure of filled and unfilled elastomers: Thermoporometric measurements
Authors: Pouchelon A. , Soria M. , Moll L.
Published: March 2011

The thermoporometry has been applied to the determination of the crosslink density of silicone elastomers. Significant effort was devoted to the choice of the solvent, only the 2‐butanone leads to the desired thermoporometric effect. The problem of the physical state of the polymer at the temperature of the experiment was pointed out. Nevertheless, the obtained results expressed by the distribution of the molecular weigth between crosslinks and their average values are compatible with those of the usual techniques and they well explain the mechanical properties of the elastomers.
Molecular mechanisms contributing to the strength and toughness of glassy polymers
Authors: Kausch H. H.
Published: March 2011

In this short summary reference will be made to some recent molecular level studies of strength. Especially the role of chains and of their entanglements in stress transfer and energy dissipation and the influence of rate of loading will be referenced.
Slow crack growth in polyethylene ‐ a review
Authors: Brown Norman , Lu Xici , Huang Yan‐Ling , Qian Ruzheng
Published: March 2011

Slow crack growth in a wide variety of polyethylenes have been investigated. The quantitative relationship between: (1) the external variables such as stress, temperature, stress intensity and J‐integral; (2) the morphological variable such as density and crystal size and (3) molecular variables such as molecular weight, branch density and branch distribution and the rate and time to failure for slow crack growth will be presented. The kinetics of slow crack growth is correlated with the microstructural changes. A fundamental description of slow crack growth is given in terms of tie molecules and the stress field on the boundary of the craze from which fracture initiates.
Chain relaxation capability and service life of polymeric materials
Authors: Brostow Witold
Published: March 2011

Behavior of polymers in creep, stress relaxation, stress‐strain curve determination, impact tests and under dynamic periodic loads are analyzed. Rapid crack propagation and slow crack propagation are considered in relation to service performance and life time. All essential aspects of mechanical behavior of polymeric materials and components have a common denominator: competition between chain relaxation capability (CRC) and destructive processes. For a given force (magnitude, rate, direction, duration) the outcome of this competition depends largely on the amount of free volume.
The effect of different hardeners on the ageing of crosslinked epoxy resins
Authors: Förster P. , Hauschildt K. R. , Wilhelm D.
Published: March 2011

Polymers based on epoxies are widely used in the industrial production of materials for different applications. The crosslinking is often done with hardeners like aliphatic or aromatic amines, with dicarboxylic acid anhydride or anionically. The resins containing mineral fillers possess similar thermal mechanical properties. On thermal oxidative ageing, however, the systems behave very differently. An account is given of the thermal mechanical behaviour and of the weight loss on ageing above the glass transition temperature. By using semiempirical molecular orbital calculations we have been able to identify a possible reason for the different thermal oxidative stability of epoxy resins crosslinked with different hardeners.
Computer simulations of thin polymer layers
Authors: Khalatur P. G.
Published: March 2011

Molecular dynamics calculations are used to explore the structure of dense monolayers of long‐chain molecules supported on a planar surface. As a model we consider ensembles of flexible chains consisting of N segments (N=32, 64 and 128) in a box with lateral (x, y) periodicity conditions. The effect of surface coverage on the conformational properties of chains is studied. At high coverages, the results of the simulations show that each chain is strongly stretched along the normal to the surface and the mean layer thickness is linear in N. The segment density distribution along the normal is found to be an universal function A2/3 f (zA1/3 N), where A is the surface area per chain. The high‐coverage distribution has a well defined broad plateau, in agreement with the so‐called blob model. In contrast to the predictions of this model, however, we observe that the chains are strongly stretched at all space scales. Differences between the results of simulations and those predicted by the mean‐field theory are also discussed.
Hydrophilic membranes based on poly(vinyl methyl ether‐crosslinked‐polystyrene) semi‐interpenetrating networks
Authors: Felisberti Maria Isabel , Stadler Reimund
Published: March 2011

Microporous membranes were prepared from poly(vinyl methyl ether ‐ crosslinked‐polystyrene) (PVME‐cross‐PS) semi‐IPN's by extraction of poly(vinyl methyl ether) (PVME) with water. Membrane morphology and properties are fixed during the process of swelling, phase separation, PVME extraction and vitrification which occurs upon immersing the samples in water. The membranes are characterized by swelling (water uptake), the relative amounts of free and bound water, and their permselectivity towards KCI solution.
Photoconductivity in polymers. Chemical structures and physical mechanisms
Authors: Strohriegl Peter , Haarer Dietrich
Published: March 2011

Synthesis and photoconductivity measurements are presented for two different types of photoconductors: i) polymers with pendant carbazolyl groups and ii) conjugated polymers. The temperature‐ and field dependence of the effective carrier mobility has been measured in a series of polymethacrylates with pendant carbazolyl groups and is discussed in relation to theoretical models. Time‐of‐flight measurements show that conjugated polymers like poly(methylphenylsilane) and poly(1,4‐phenylenevinylene) exhibit extremely high carrier mobilities.
Ferrocene containing polymers
Authors: Nuyken Oskar , Burkhardt Volker , Pöhlmann Thomas , Herberhold Max
Published: March 2011

Polymers with pendent ferrocene units are synthesized by radical and anionic methods. It has been demonstrated that polymer‐analogous reactions are an attractive alternative to prepare those polymers. Polymers with ferrocene units in the main chain are available from interfacial condensation reaction between ferrocene‐1,1′‐dicarbonic acid dichloride with α, ω‐diamines. Addition of ferrocene‐1,1′‐dithiol onto norbornadiene yields a polymer with repeating units from ferrocene disulfide and norbornene and nortricyclane end‐groups. End‐capping reactions of α, ω‐dimercapto‐telechelics with vinylferrocene yield polymers with ferrocene end‐groups.
Synthesis and investigation of new organometallic polymers on the basis of polyacrylonitrile
Authors: Valetsky P. M. , Bronstein L. M. , Loginova T. P.
Published: March 2011

The regularities of complex formation of PAN nitrile groups with hexacarbonyls of VIB group metals were studied. PAN metal carbonyl complexes with various degrees of complexation were synthesized. Thermal transformations of PAN metal carbonyls were investigated. It was shown that the thermal changes of PAN chromium carbonyls are anomalous, but this does not prevent from the formation of polyconjugated areas and the enchancement of conductivity.
Theory of steric stabilization of colloid systems by grafted polymers
Authors: Ekaterina B.Zhulina , Oleg V.Borisov
Published: March 2011

An analytical mean‐field theory of steric stabilization of dispersions by non‐charged polymer chains grafted at one end onto the surface of colloid particles has been developed. The chains were assumed to be grafted densly, so that the neighboring coils overlap and form a single stabilizing layer. In the case of low‐molecular‐weight dispersing medium and relatively loose stabilizing layers the shape of the potential curve of interparticle interaction is determined by the value of magnified image is the Hamaker constant and Γ is the surface concentration of stabilizing polymer) and the quality of the dispersing medium as a solvent for polymer chains. Depending on the value of γ the system may exhibit the stability of both thermodynamic ( α<1 ) and kinetic ( α> 1 ) character. When the molecules of the dispersing medium are short polymer chains the increase in their length leads to a drastic decrease in the stability range of the system and to its destabilization.
Growth process of polymers near the gelation threshold
Authors: Adam M.
Published: March 2011

We will review experimental results obtained recently on the determination of the laws governing the growth process of polymer clusters as the gel point is approached. The exponent γ which characterizes the increase of the mean weight‐average molecular weight Mw as the gel point is approached and the exponent τ which characterizes the mass distribution were measured on different chemical systems. They were found to be independent of the chemical system (within experimental error) and very close to exponent values calculated by computer simulations following the percolation model. Therefore, the sol‐gel transition is a critical phenomenon of connectivity belonging to the same class of universality as percolation.
The evolution of viscoelasticity near the gel point of end‐linking poly(dimethylsiloxane)s
Authors: Scanlan James C. , Winter H. Henning
Published: March 2011

The linear viscoelasticity of polymers near the gel point can be described by two scaling laws. The material at the gel point has a power‐law linear viscoelastic relaxation modulus, and the relaxation exponent has been found to vary with the composition of the precursor materials, i.e., it is not universal for gelation. A second scaling law describes the evolution of the linear viscoelastic properties through the gel point. The rate of change of the dynamic mechanical modulus/viscosity is observed to scale as a power‐law function of frequency. This power‐law function defines a dynamic critical exponent, and this has been found to be independent of precursor composition for end‐linking poly(dimethylsiloxane) polymers and equal to κ = 0.21 ± 0.02. This exponent may be a universal measure of gelation. The technique of Time Resolved Mechanical Spectroscopy is used to observe the evolution of linear viscoelastic properties of crosslinking polymers in situ in the rheometer. A stretched exponential relaxation modulus describes the evolution of mechanical properties in the vicinity of the gel point very well. The exponents which characterize the divergence of the zero‐shear viscosity and the equilibrium modulus are not universal, since they are related to the relaxation exponent and the dynamic critical exponent.