bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of pseudostationary radical polymerization, 3. Periodic modulation of the termination process for termination by disproportionation
Authors: Zifferer Gerhard , Olaj Oskar Friedrich
Published: April 2003

A procedure is developed that allows the calculation of chain‐length distributions of polymers prepared by periodic modulation of the termination rate constant, considering termination by disproportionation. Applying some (hypothetical) field which suppresses — or at least diminishes — the termination rate constant periodically, results in step‐function‐like chain‐length distributions. In principle, the same information may be obtained as in the case of periodical variation of the rate of initiation.
Molecular weight distribution of a living polymer generated from a bifunctional initiator with non‐equal initiation rate constants
Authors: Dong Hai , Yan Deyue
Published: April 2003

This work deals with the kinetics of the living polymerization initiated by a bifunctional initiator with different rate constants of the first and the second step of initiation. The expressions of the molecular weight distribution (MWD) function, the number‐ and weight‐average degrees of polymerization and the polydispersity index were derived rigorously. Numerical results show that the nonequal initiation rate constants often lead to a bimodal MWD except the ratio of ki to ki′ being very large (>500, for instance) or relatively small (<1, for example). The MWD of the resultant polymer is rather narrow even in the presence of double peaks. With decreasing initiator concentration, the MWD at full conversion becomes narrower, and the shoulder peak of the MWD curve declines.
Simultaneous determination of free‐radical propagation and transfer rates from a novel type of PLP‐SEC experiment
Authors: Buback Michael , Laemmel Ralf A.
Published: April 2003

A novel type of pulsed laser polymerization (PLP)‐size exclusion chromatography (SEC) experiment is presented in which laser pulse sequences are applied at considerable dark time intervals between each pulse package. The pulse sequences give rise to the characteristically structured molecular weight distribution (MWD) from which kp may be derived. Polymer produced during the extended dark time intervals determines the MWD at high molecular weights and allows for the measurement of chain transfer rates. The method by which propagation and transfer rates are accessible from one experiment is illustrated by simulations using the program package PREDICI.
Application of a tie molecule model to the postyielding deformation of crystalline polymers
Authors: Takayanagi Motowo , Nitta Koh‐hei
Published: April 2003

Our past paper reported that the postyielding deformation of crystalline polymers such as polyethylene (PE), poly(oxymethylene) (POM), poly(propylene) (PP) and nylon 6 (Ny 6) was expressed by master curves with a characteristic constant for each polymer when normalized true stress and true strain are plotted in both logarithmic graphs and suitably shifted. For a molecular understanding of the postyielding process, we present a tie molecule model which assumes that the tie molecules are pulled out from the lamellar fragment at a constant number of tie molecules. The limit in applicability of the model is in the final stage of fiber formation. Fundamental equations of the model are solved to give a critical point at which all the molecular parameters can be uniquely determined from the characteristic constant for each polymer. At the critical point, the tie molecule length monotonously increases at a fixed number of tie molecules. The limit of the tie molecule length increases in the order of PE, POM, PP and Ny 6. By using an empirical relationship between the area fraction of tie molecules and the degree of crystallinity of these polymers, it is found that the order of area fraction of the tie molecules in Ny 6, PP, POM and PE is entirely reversed to the order of weight fraction of the tie molecules of the above polymers.
Spatial extension of the bipolaronic defect in highly conducting polymers based on five‐membered aromatic rings
Authors: Alemán Carlos
Published: April 2003

The molecular geometries of neutral and dicationic oligomers comprising 7, 10, 13 and 16 rings of thiophene, furan and pyrrole were determined using quantum mechanical calculations. The usual benzenoid structure was characterized for neutral oligomers, whereas a quinoid structural defect which extends over six rings was found for dications. Analysis of the transition region, where the quinoid structure changes to the benzenoid one, revealed structural differences between thiophene, furan and pyrrole derivatives.
Strain‐dependent dynamic properties of filled rubber network systems, 2: The physical meaning of parameters in the L‐N‐B model and their applicability
Authors: Lin Chen‐Ron , Lee Yu‐Der
Published: April 2003

In Part 1 of this series, the strain‐dependent dynamic properties of filler loaded rubber systems were modelled with a newly derived L‐N‐B (links‐nodes‐blobs) model. In this paper, the physical meaning and significance of parameters of the L‐N‐B model are described and compared with experimental results. Furthermore, with the combination of a van der Waals force model, these parameters can be described in terms of basic physical material properties of filler and rubber matrix. The temperature dependence of dynamic properties of filled rubbers is successfully described in terms of the series combination of the angular deformation element \documentclass{article}\pagestyle{empty}\begin{document}$\frac{{2d\bar G}}{{mL_1 a^2 }}$\end{document} in series with the tension element \documentclass{article}\pagestyle{empty}\begin{document}$\frac{{dQ}}{{L_1 a^2 }}$\end{document}. Moreover, the normalized storage modulus can be expressed as a master curve \documentclass{article}\pagestyle{empty}\begin{document}$Z_{L - N - B} = {\rm Ei}\left[ {\frac{{ - a_2 mQ\varepsilon _b }}{{2d\bar G}} \bullet L_1 } \right]/{\rm Ei}\left[ {\frac{{ - a_2 mQ\varepsilon _b }}{{2d\bar G}}} \right]$\end{document}. The parameter \documentclass{article}\pagestyle{empty}\begin{document}$\frac{{ - a_2 mQ\varepsilon _b }}{{2d\bar G}}$\end{document} is almost a constant for different carbon black filled systems. The distributions of blob and link in a L‐N‐B model are similar for carbon black filled rubber systems. The applicability and the limitation of the L‐N‐B model are also discussed and illustrated with experimental results. Beside carbon black filled rubber systems, silica filled rubber and filler‐in‐oil systems are discussed.
Intramolecularly ordered globules and the collapse of short chains
Authors: Ganazzoli Fabio
Published: April 2003

We investigate the poor‐solvent collapse of short chains having different stiffness through self‐consistent minimization of the intramolecular free energy under the constraint of fixed segment lengths between adjacent beads. At first the chains form the Random Gaussian Globule, where the beads are distributed at random at the same average distance from the centre of mass, while the segments show very little correlation. At a larger attractive potential, this collapsed globule undergoes a transition to one or more ordered compact states, depending on the chain stiffness. Under very strong contraction, all chains are described as a Compact Ordered Globule: the beads are again at a constant average distance from the centre of mass, while the segments jump back and forth at the globule's wall with a very large correlation. At intermediate contraction, the thinner and stiffer chains form the Oscillating Ordered Globule wherein the beads are alternatively distributed on two concentric on two concentric shells. In this case, we also find metastable states with nonsymmetrical conformations of the chain with respect to its ends. We also briefly discuss the thermodynamics of the coil‐globule and globule‐globule transitions, showing that in long polymer chains these ordered conformations cannot involve the whole chain. However, we suggest that they might still be found as local globules that form for kinetic reasons.
Stereoselectivity of an early propagation step in the anionic polymerization of methyl methacrylate – ab initio SCF, MNDO and AM1 study
Authors: Dybal Jiří , Kříž Jaroslav
Published: April 2003

On the basis of previous experimental and theoretical studies of low‐molecular models of living poly(methyl methacrylate) and their coordination interactions, molecular states preceding and involving the propagation step of the anionic polymerization of methyl methacrylate (MMA) were investigated. Previously published structures of the intracoordinated form of the model dimer dimethyl 2‐lithio‐2,4,4‐trimethylglutarate (DMMALi) and its free anion (DMMA) optimized using ab initio SCF 3‐21G were reinspected and a new, similar but more stable, geometry was found. AM1 and ab initio 3‐21G calculations of the addition of MMA to the anion derived from methyl isobutyrate were used to explore the applicability of semiempirical methods to the present problem. Intermediate complexes and transition states of the iso‐ and syndiotactic addition of MMA to DMMA and DMMALi were simulated using MNDO and AM1. The activation energy of MMA addition to DMMA is predicted to be substantially lower for the syndiotactic transition state. In contrast, only isotactic MMA addition is possible to the energetically favored intra‐coordinated form of DMMALi (c‐DMMALi). Syndiotactic addition to the uncoordinated form of DMMALi is apparently possible according to MNDO. Considering the earlier finding that c‐DMMALi is favored by dilution and lower temperature in solvating media such as tetrahydrofuran, the differences in stereoregularity of the anionic polymerization of MMA caused by concentration, temperature or solvent polarity can be plausibly explained.
Statistical branching of heterochains
Authors: Tobita Hidetaka
Published: April 2003

A general theory for the statistical branching of heterochains is proposed on the basis of the random sampling technique. Consider a polymer mixture that consists of N types of chains whose weight fractions are wi (i = 1, 2, …, N), and number‐ and weight‐average chain lengths are P̄np,i and P̄wp,i, respectively. Suppose the transition probability that a branch point on a chain of type i is connected to a chain end of a type j chain is given by pij. When the branching density of chains of type i is ρi, the weight‐average chain length is given by \documentclass{article}\pagestyle{empty}\begin{document}$\bar P_w = W\sum\nolimits_{m = 0}^\infty T ^m \sum\nolimits_{n = 0}^\infty {SU} ^n 1$\end{document}, where S is the diagonal matrix whose elements are \documentclass{article}\pagestyle{empty}\begin{document}$S_{ii} = \bar P_{wp,i}$\end{document}, 1 is the column vector whose elements are all unity, U is the transition matrix whose elements are given by \documentclass{article}\pagestyle{empty}\begin{document}$u_{ij} = \rho _i p_{ij} P_{np,j} ,T$\end{document} is another transition matrix whose elements are given by tij = (wj/wi)Uji, and W is the row vector whose elements are wi. Simpler expressions of P̄w are presented for binary systems. In addition to the multicomponent systems, the present equation could also be used such as for free‐radical polymerization with long‐chain branching, by considering primary chains formed at different times as different types of polymer chains. For the prediction of the full molecular weight distribution, a Monte Carlo simulation method is used to illustrate the resulting distribution profiles.
Geometric properties of micelles formed by triblock copolymers and solubilizates in dilute solutions
Authors: Xing Li , Mattice Wayne L.
Published: April 2003

In this work we study the geometric properties of the triblock copolymer micelles with solubilized low‐mass molecules in a selective solvent using the Monte Carlo technique on a cubic lattice. The triblock copolymers are of the ABA type, with the two insoluble blocks at the ends. The size of the micelles is characterized by the squared radius of gyration of the micellar core, Rg2, while the shape is treated by the asphericity b and the acylindricity c, which are defined in terms of the principal moments of the radius of gyration tensor. The parameters varied are the amount of solubilizate molecules, the polymer concentration, the interaction parameters between A and B, A and solvent, solute and solvent, solute and B block, and the A and B block length. The micelle size, characterized by Rg2, grows with increasing concentration of the solubilizates and/or the polymer, and stronger interactions between the incompatible species. The A block length is found not to modify Rg2 monotonously, while an increase in B block length results in a decrease in Rg2 at high concentrations. As the size expands, the micellar shape becomes less spherical but retains its cylindricity. In addition to an increase in the averaged Rg2, the distribution of Rg2 becomes broader and the system less homogeneous.
Atomistic monte carlo simulations of polymethylene fluids
Authors: Vacatello Michele
Published: April 2003

Atomistic Monte Carlo simulations of polymethylene fluids in various environments have been of great importance for improving our understanding of the molecular arrangements and conformations in systems of chain molecules. This paper describes models, calculations and principal results of a number of simulations performed in the last two decades for liquid alkanes in bulk and in the proximity of solid surfaces, and for systems of long chain amphiphilic molecules in monolayers, double layers, micelles and droplets.
Chain‐length dependent termination in pulsed‐laser polymerization, 1. Interaction with propagation
Authors: Olaj Oskar Friedrich , Kornherr Andreas , Zifferer Gerhard
Published: April 2003

Using a new simulation procedure in which each individual propagation step is subjected to a Poisson process it was proved that in case of chain‐length dependent termination the apparent rate of propagation no longer coincides with the true one. This is caused by the polydispersity of the chain‐length distribution of the growing chains: shorter chains are removed preferentially. This effect is comparatively small although significant. The consequences for the determination of the rate constant of chain propagation kp are nearly negligible.
A fast way of solving Jonah and coworkers' equations to evaluate anisotropic‐isotropic transition temperatures of semirigid polymers
Authors: Figari Giuseppe , Costa Camilla
Published: April 2003

A fast and simple method has been found to solve the set of equations recently proposed by Jonah, Brostow and Hess [Macromolecules 26, 76 (1993)], allowing the evaluation of the anisotropic‐isotropic transition temperature for a semirigid liquid polymer. Starting with given values of η (average length of the rigid sequences coexisting with flexible sequences inside the semiflexible polymer chains) and θ (degree of rigidity of the semirigid polymer), a reduced transition temperature τ is readily obtained, together with the transition values of the anisotropic order parameters s and γ.
On the product distribution of degradable polymers
Authors: Carl Wilfried
Published: April 2003

We present a simplified model for calculating the product distribution of degradable polymers which is based on a grand canonical approach. The distribution depends on two physical parameters, the energy of a bond formation and the initial concentration of monomers. Due to its simplicity this model covers the two limiting cases, namely a polymerization process (no degradation) and micellar association (dominant degradation), and allows for straightforward extension to branched chain topologies or flow fields. In shear flow, a flow rate dependent length distribution leads to shear thinning.
Distribution of the shape asymmetry of linear and star‐branched random walks
Authors: Zifferer Gerhard
Published: April 2003

Linear and star‐branched (off‐lattice) random walks with up to F = 96 arms and a total chain‐length of 961 segments have been produced by means of Monte Carlo simulation. The probability distribution of the asphericity δ*–a quantity ranging from 0 in case of perfect radical symmetry to 1 for completely elongated (rodlike) shapes–has been calculated. In addition, the correlation between δ* and other shape‐descriptors as well as between δ* and quantities characteristic of the size of configurations have been evaluated. In accordance with existing literature the distribution H(δ*) of δ* is found to be very broad in case of linear chains. With increasing number of arms. H(δ*) becomes sharper but for F = 96 still ranges within an interval [0, ≈0,05]. Of course, other shape descriptors are directly correlated with the asphericity. Actually, for all functionalities evaluated, the global size of configurations is strongly correlated with δ* as well: the larger the asymmetry the larger the dimensions of the configuration under consideration.
Grafted polymers under strong shear: Scaling and non‐equilibrium Monte Carlo studies
Authors: Lai Chee‐Yuen , Lai Pik‐Yin
Published: April 2003

End‐grafted polymer chains exposed to strong shear solvent flow in the x‐direction are investigated by a non‐equilibrium Monte Carlo method using the bond‐fluctuating model. The solvent flow is modelled by an enhanced jump rate of monomers in the flow direction. Under strong enough shear flow, the shear force is non‐linear with the blob size ζ depending on the shear force and not on the monomer volume fraction ϕ. For the case of a grafted single chain, our data on the end‐to‐end distance of the polymer for a wide range of shear rate γ agree well with the proposed scaling form and compare reasonably well with the Langevin force law in the extreme strong shear case. Also the scaling for the blob size is derived with ζ = aNvK(γN2+v) for some scaling function K, and verified by our simulation data. For the case of a polymer brush, we derive the crossover force scale F* separating the weak and strong shear regime with F*a/(kT) = ϕv/(3v−1) where v is the usual self‐avoiding walk exponent. For the case of a polymer brush under strong shear, the velocity profile, v(z), inside and above the brush is calculated analytically by treating the flow as in a porous medium and solving the Brinkman equation. The solution of the velocity profile is then combined with non‐equilibrium Monte Carlo simulation data which allow a self‐consistent determination of the chain end‐to‐end length and the incline angle of the chain. Also we derive the scaling form for the positions x(n) of the nth monomer and verify it by our simulation data. We further obtain an analytical expression for x(n) in terms of the effective viscosity η of the model, given by F = ηav(z). The effective viscosity is also found from our simulation to be ηa2/(kT) ≃ 0.02 ± 0.005.
On the importance of including intermolecular correlations in the measurement of polymer interdiffusion by fluorescence nonradiative energy transfer
Authors: O'Neil Gregory A. , Torkelson John M.
Published: April 2003

There has been a great deal of recent interest in monitoring polymer interdiffusion with fluorescence nonradiative energy transfer (NRET), a typical experiment consisting of polymer chains labeled with a donor chromophore interdiffusing with chains labeled with an acceptor chromophore, causing an increase in energy transfer efficiency, E. A factor nearly always ignored in models of this process is the fact that chromophore interactions are screened out because of intermolecular correlation effects, leading to a lower E than would otherwise be expected. The model of Dhinojwala and Torkelson (Macromolecules 27, 4817 (1994)) has been modified to include correlations in order to explore the impact that ignoring correlations has on the diffusion coefficients calculated in such experiments. When correlations are included in the model, E is proportional to (Dpt)1/2/x for t<x2/(16Dp) (where x is the thickness of the donor‐labeled film and Dp is the polymer diffusion coefficient), similar to when correlations are ignored. Within this linear regime errors in Dp associated with ignoring correlations are typically less than 20% for logically defined systems, which may be insignificant given the uncertainty with which diffusion coefficients are normally reported. However, this study clearly demonstrates that precautions should be used in all experiments of this type to stay in this linear regime, as improperly accounting for or ignoring correlation effects at longer diffusion times can lead to the spurious result that apparent diffusion coefficients decrease with annealing time, by factors of 2 to 5 to as much as an order of magnitude or more at sufficiently long time. Systems designed to minimize correlation effects should have a large Förster radius and a sufficiently high ratio of acceptors to donors; with such a situation and the use of NRET data from the linear regime of E vs. t1/2, it is possible under many experimental circumstances to determine diffusion coefficients within small error even when the effects of correlations are ignored.
Distribution functions and dynamical properties of stiff macromolecules
Authors: Winkler Roland G. , Harnau Ludger , Reineker Peter
Published: April 2003

An analytically tractable model for chain molecules with bending stiffness is presented and the dynamical properties of such chains are investigated. The partition function is derived via the maximum entropy principle taking into account the chain connectivity as well as the bending restrictions in form of constraints. We demonstrate that second moments agree exactly with those known from the Kratky‐Porod wormlike chain. Moreover, various distribution functions are calculated. In particular, the static structure factor is shown to be proportional to 1/q at large scattering vectors q. The equations of motion for a chain in a melt as well as in dilute solution are presented. In the latter case the hydrodynamic interaction is taken into account via the Rotne‐Prager tensor. The dynamical equations are solved by a normal mode analysis. In the limit of a flexible chain the model reproduces the well‐known Rouse and Zimm dynamics, respectively, on large length scales, whereas in the rod limit the eigenfunctions correspond to bending motion only. In addition, the coherent and incoherent dynamic structure factor is discussed. For melts we show that at large scattering vectors the incoherent dynamic structure factor is a universal function of only the combination q8/3tp1/3, where 1/(2p) is the persistence length of the macromolecules. The comparison of the theoretical results with quasielastic neutron and light scattering experiments of various polymers in solution and melt exhibits good agreement. Our investigations show that local stiffness strongly influences the dynamics of macromolecules on small length scales even for long and flexible chains.
Distributions of cyclic oligomers formed by irreversible step‐growth polymerisation. Results from kinetic modeling
Authors: Ercolani Gianfranco , Mencarelli Paolo
Published: April 2003

The distribution of cyclic oligomer concentrations (examined up to the cyclic pentamer) in the process of step‐growth polymerisation decreases, in concentrated solution, with i−2.5 if the chains follow Gaussian statistics (i: degree of polymerization). This picture is analogous to that shown by cyclic oligomer distributions obtained under thermodynamic control and is in contrast with that shown by cyclic oligomer distributions obtained by irreversible chain‐growth polymerisation which is characterized by a gradient of −1.5. This result has been initially obtained by numerical integration of the differential rate equations pertinent to a kinetic model relative to the reaction of a bifunctional reactant A—B under batchwise conditions, and then confirmed by analytical integration of the differential rate equations under the condition that propagation is much faster than cyclisation. The case in which the monomeric ring is strained has been also investigated. Also in this case the obtained distribution is analogous to that shown under equilibrium conditions. From an examination of the distributions of the ring yields, the best conditions for the preparation of either the cyclic monomer or the cyclic dimer are suggested.
Chain‐length‐dependent termination rate constant: Effect on molecular weight distributions formed by pulsed laser radical polymerization
Authors: Ntkitin Anatolij N. , Evseev Alexander V.
Published: April 2003

For polymerization initiated by an arbitrary sequence of laser pulses a numerical technique for calculating molecular weight distributions (MWDs) is developed, which takes into consideration the chain length dependence of the termination rate constant kt. The MWDs for methyl methacrylate and styrene are calculated by use of α and k0 values (for the law k = k0(i)−α of termination of radicals with chain length i) and averages \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {(i,{\rm }j)} $\end{document} (for rate constants k = k0\documentclass{article}\pagestyle{empty}\begin{document}$ \overline {(i,{\rm }j)} $\end{document} of termination of radicals with different degrees of polymerization) taken from the literature. The dependences of the overall termination constant 〈kt〉 on initiation parameters (pulse repetition rate (v) and pulse intensity for initiation by periodic laser pulses) are presented. Two methods are proposed for α and k0 determination: (a) by experiments on polymerization with periodic laser pulses where monomer‐to‐polymer conversions per pulse are determined for different v; (b) by experiments on polymerization with packets of pulses where the constant kp (the rate constant of propagation), α and k0 can be determined simultaneously from MWD. For both methods simple analytical equations are derived for evaluation of the constants. The limits of application of the methods are determined by use of the numerical technique for MWD calculation.
Theoretical study on the linking process of divinyl compounds with living precursors, 1. Uniform precursor chains
Authors: Yan Deyue , Zhou Zhiping
Published: April 2003

The theoretical aspect of the linking reaction between divinyl compounds and uniform living precursors has been studied by using the model of threads going through the holes of buttons. The expressions of various molecular parameters of the clusters formed during the linking process, such as the number‐ and the weight‐average molecular weights, the average degree of branching, the branch distribution function, and the molecular weight distribution function, were rigorously derived. The critical condition of gelation is given as well. The theoretical results obtained are appropriate to the core formation process for the core‐first preparation procedure of star‐shaped polymers, and to the arm‐first approach using a uniform living precursor with low or moderate molecular size.
Concentration dependence of static chain properties, 1. Monte carlo simulations in a cubic lattice
Authors: Olaj Oskar Friedrich , Petrik Thomas , Zifferer Gerhard
Published: April 2003

Monte Carlo simulations of 5‐way cubic lattice chains have been performed over the whole concentration range starting with the isolated chain up to totally dense systems devoid of any vacancies. Athermal as well as θ‐conditions have been investigated in order to give a complete description of the changes with respect to the global size and shape characteristics of the coils on the one hand and to connect these findings to the behaviour of local bond‐structures on the other hand. Especially, we have found that the global dimensions of an isolated θ‐chain are already reached by bulk chains at a volume fraction of approximately 0,7. However, the comparable global size and shape is realized in a totally different way on a local scale which is obviously due to the different behaviour of inter‐ and intramolecular forces.
Optimal screening distance for ulnar neuropathy at the elbow
Authors: Landau Mark E. , Barner Kristen C. , Campbell William W.
Published: April 2003

Focal demyelinating lesions typically occur within a 1‐cm segment of a nerve. In electrodiagnostic studies, measurements over longer distances decrease the chance of detecting such lesions, but measurements over shorter distances result in greater experimental error. Our objective was therefore to determine the optimal screening distance for ulnar neuropathy at the elbow (UNE) incorporating previously derived experimental errors for calculating nerve conduction velocity (NCV). Using a lesion model wherein prolongation of 0.4 ms was added to the expected latency of a 1‐cm nerve segment, new NCVs were derived for distances between 1 and 10 cm for nerves normally conducting between 40 and 65 m/s. Lesion detection, or sensitivity, was defined as the likelihood of calculating a decrease of 10 m/s from the normal NCV while including the experimental error. Specificity was related to the likelihood of an inadvertent calculation of such a decrease in NCV in a segment without a lesion. Sensitivity and specificity were derived at multiple distances with varying NCVs. The total percentage error was the sum of the false‐negative and false‐positive percentages. The least total percentage error occurred at 3–4 cm, 4–6 cm, and 6–8 cm for nerves normally conducting at 40–50 m/s, 50–60 m/s, and 60–65 m/s, respectively. We conclude that the optimal distance for screening UNE, considering both sensitivity and specificity, is significantly less than 10 cm, perhaps as low as 4–6 cm; considering in addition the likely locations of focal lesions, the best distance is 6–8 cm. Muscle Nerve 27:570–574, 2003
Surface electromyographic recording of volitional activity: A technique to detect partial motor conduction block
Authors: Chaudhry Vinay , Corse Andrea , Skolasky Richard L.
Published: April 2003

Partial motor conduction block, an electrophysiological hallmark of demyelination, helps to identify acquired demyelinating neuropathies but its electrophysiological detection can be difficult. We report a technique that may be helpful in this regard. Twenty‐five patients with partial motor conduction block secondary to acquired demyelinating polyneuropathy (ADP), 7 with amyotrophic lateral sclerosis (ALS), 7 with stroke, and 11 control subjects, were studied. Amplitude of compound muscle action potentials was recorded after distal electrical (E) stimulation and for volitionally (V) induced responses in 82 muscles. Mean ± SD V/E ratio was 12.3 ± 6.6 for ADP patients, 58.1 ± 17 for ALS patients, 11.4 ± 9 for stroke patients, and 55.4 ± 12.3 for controls. The V/E ratios for patients with partial motor conduction block and stroke were significantly reduced compared with ALS patients and healthy controls (P < 0.05). Surface electromyographic (EMG) recording for determination of the V/E ratio may be a useful technique for detection of a proximal conduction block if a central lesion or poor effort can be excluded. Further study of this novel technique is necessary. Muscle Nerve 27: 590–594, 2003
Neuromuscular and musculoskeletal problems in instrumental musicians
Authors: Lederman Richard J.
Published: April 2003

Over the past 20 years, there has been increasing interest in the medical problems of performing artists. In this review, the major playing‐related disorders seen in instrumental musicians are discussed. Among the 1353 instrumentalists personally evaluated, the major diagnoses included musculoskeletal disorders in 64%, peripheral nerve problems in 20%, and focal dystonia in 8%. Of these instrumentalists, 60% were women, although men were the majority in the group with focal dystonia. The average age at the time of evaluation was 37 years for men and 30 years for women. Among musculoskeletal disorders, regional muscle pain syndromes, particularly of the upper limb, upper trunk, and neck, were most common. Specific entities such as tendinitis and ligament sprain were less common. Frequent peripheral nerve disorders included thoracic outlet syndrome, ulnar neuropathy at the elbow, and carpal tunnel syndrome. Each instrument group showed a characteristic distribution of symptoms and signs that appeared to be directly related to the static and dynamic stresses inherent in the playing of the instrument. Electrodiagnostic studies are an important part of the evaluation of these disorders, particularly nerve entrapment syndromes. With carefully designed treatment, the majority of instrumental musicians can return to full and pain‐free playing. Nerve entrapment syndromes have the highest treatment success rate, followed by musculoskeletal pain syndromes. Despite some recent innovative approaches, focal dystonia remains largely resistant to therapy. Muscle Nerve 27: 549–561, 2003
Perugia urodynamic method of analysis (PUMA): A new advanced method of urodynamic analysis applied clinically and compared with other advanced methods
Authors: Porena Massimo , Biscotto Sauro , Costantini Elisabetta , Mearini Ettore , Verdini Livio
Published: April 2003

Aims

The aim of this study is to compare PUMA curves with different pathologic conditions causing bladder dysfunction in 158 men and 83 women.

Methods

PUMA results in terms of bladder outlet obstruction and detrusor contractility were compared in 92 men with benign prostatic hypertrophy (BPH) and pves≅pdet (i.e., pabd≅0) with the results of the urodynamics operator's opinion, the provisional International Continence Society method, Abrams and Griffith's diagram, urethral resistence factor (URA), Schäfer's diagram, and Watt factor. PUMA curves correlated reliably with different pathologic conditions such as obstructive BPH, orthotopic bladder, cystocele, the neurological bladder, and bladder diverticulum. Statistical analysis indicated excellent agreement between PUMA and URA; agreement with other methods was good in cases of obstruction and nonobstruction. In doubtful cases, as diagnosed by standard methods, PUMA agreed only with the Abrams and Griffith's diagram. PUMA and Wmax were in good agreement on detrusor con traction force. Agreement between PUMA and Schäfer's diagram was excellent for patients with detrusor hypercontractility and good for patients with detrusor hypocontractility and normocontractility. PUMA is the only method applicable to women. It is easy to perform. When integrated with other diagnostic tests, it provides realistic data for diagnosis, medical or surgical therapy, and outcome. Neurourol. Urodynam. 22:206–222, 2003. © 2003 Wiley‐Liss, Inc.
Bladder filling by autologous urine production during cystometry: A urodynamic pitfall!
Authors: Heesakkers John P.F.A. , Vandoninck Vera , van Balken Michael R. , Bemelmans Bart L.H.
Published: April 2003

Aims

The rate of autologous urine production should not have a major disturbing influence on cystometric urodynamic parameters such as first filling sensation, normal desire to void, strong desire to void, and cystometric bladder capacity. Instructions to patients and drinking behavior can have considerable impact, especially if filling cystometry is preceded by free uroflowmetry. We studied the influence of autologous urine production during filling cystometry on total bladder volume.

Methods

Urodynamic investigations performed between September of 2000 and February of 2001 were analyzed. Only those urodynamic investigations for which total bladder capacity could be calculated were taken into account (i.e., catheterization before and after cystometry and no urine loss during the investigations).

Results

After screening, 186 investigations were used for further analysis. Mean filled volume (external infusion plus autologous urine production) was 346 ± 152 mL, but mean real bladder capacity (i.e., voided volume + residual urine) was 391 ± 170 mL. In all patients, 14% extra urine was produced due to autologous urine production (mean filling rate, 6.1 mL/min). In 42% of the investigations, the real bladder capacity was more than 110% of the infused volume. In 18% of the patients, the contribution of natural bladder filling was more than 25% of the infused volume.

Conclusions

Natural bladder filling plays a substantial role during filling cystometry and has a disturbing influence on calculated urodynamic parameters. Attention should be paid to patient instructions before the urodynamic investigation. The combination of free uroflowmetry followed by filling cystometry should be avoided. This avoidance is especially important if interventional studies are performed. Careful interpretation of studies depending on bladder capacity parameters is mandatory, and such parameters should be corrected for autologous bladder filling. Neurourol. Urodynam. 22:243–245, 2003. © 2003 Wiley‐Liss, Inc.
Determining the reliability of ultrasound measurements and the validity of the formulae for ultrasound estimation of postvoid residual bladder volume in postpartum women
Authors: Yip Shing‐Kai , Sahota Daljit , Chang Allan Ming‐Zing
Published: April 2003

Aims

To determine the reliability and validity of ultrasonic assessment of the postvoid residual bladder volume (PVRBV) in postpartum women.

Methods

Ultrasound estimated PVRBVs were performed on 99 consecutive women with postpartum urinary retention, to validate 12 published bladder volume‐estimation formulae. This ultrasound‐predicted volume was compared with the immediately collected catheterized volume. Comparison of individual formula with the catheterized volumes was performed by using the Intraclass Correlation Coefficient (concordance), and difference plots (bias, linearity of the difference). All volumes were transformed logarithmically to ensure a normal distribution.

Results

The postpartum bladder maintained its ellipsoid appearance. One‐way analysis of variance showed the variance of the individual formulae ranged from 83.42 to 3463.66 (SD 9.13 to 58.85). The four formulae with the least variance had an intraclass correlation coefficient ranging from 0.93 to 0.96, and a mean difference between volume estimated by the formula and catheterized volume ranging from −0.05 to −0.11 (SD 0.09 to 0.11). The error between the value predicted by the formulae and that of the catheterized volume was linear in only one formula: Volume = (π × W × Dl × H) ÷ 6.

Conclusions

The results of this study have shown that ultrasonic assessment of the PVRBV in the postpartum period is accurate, and it can be used as a guide to whether transurethral catheterization is necessary. Neurourol. Urodynam. 22:255–260, 2003. © 2003 Wiley‐Liss, Inc.
The formation of polymerizable tubules
Authors: Lando J. B. , Hansen J. E. , Sudiwala R. V. , Rickert S. E.
Published: April 2003

We have been investigating the crystallization behavior of the phospholipid amphiphile, 1,2 bis (10, 12‐tricosadiynol)‐sn‐glycero‐3‐phosphocholine, DC8,9PC, which forms both vesicles and hollow tubules as well as Langmuir Blodgett monolayers and multilayers. This material has polymerizable diacetylene groups in equivalent positions on the two hydrocarbon tails. The direct crystallization from solution of this amphiphile has been studied using different solvent mixtures and temperatures. The Langmuir Blodgett technique was also used to compress and orient the tubules.
Development of polyaniline–lithium secondary battery
Authors: Matsunaga Tsutomu , Daifuku Hideharu , Nakajima Tadashi , Kawagoe Takahiro
Published: April 2003

A series of coin‐type lithium secondary batteries with polyaniline positive electrodes was developed and commercialized which might be not only the first practical polymer battery but also the first industrial application of conducting polymers. Performances of the commercialized batteries were described in detail in this paper.

In order to achieve the development the most important thing was the optimization of molecular structure and molphology of multiguise polyaniline as the electrode material. According to the findings obtained during the development, polyaniline sheet was prepared substantially to be composed of imino‐1,4‐phenylene (IP) and the cation radical of IP (IP+) by the novel procedure, not to include quinoid configuration of polyaniline (NP) which was proved to be electrochemically inactive in non‐aqueous systems.
Mechanical and dielectric relaxations in liquid crystalline copolyesters
Authors: Green D. I. , Davies G. R. , Ward I. M. , Alhaj‐Mohammed M. H. , Jawad S. Abdul
Published: April 2003

Dynamic mechanical measurements in tension and torsion on oriented tapes and monofilaments of a range of liquid crystalline polyesters have been combined with dielectric measurements to obtain a molecular understanding of the relaxation processes.

This paper extends our previous work [1,2,3] on polyesters of hydroxybenzoic acid (HBA) and hydroxynaphthoic acid (HNA) to related polymers containing dihydroxynaphthalene (DHN) and terephthalic acid (TPA) or biphenyl (BP) and TPA in place of the HNA. It confirms the association of the β and γ processes with naphthyl and phenyl moieties but shows that the processes cannot be due simply to the independent motions of single units.
Synthesis and degradation of cyano‐containing aramids
Authors: Kim S. , Pearce E. M. , Kwei T. K.
Published: April 2003

Various aramids having a cyano group on the diamine ring were synthesized. Aramids containing a cyano group ortho to the amide bond underwent thermal degradation via a two step mechanism, whereas those containing a cyano group meta to the amide bond did not. The first step represented the loss of HCN resulting in benzoxazole polymers, which degraded further in the second stage producing high char yield at 900°C. The thermal studied of copolyamides from m‐phenylenediamine, 2,4‐diaminobenzonitrile, and iso‐ or terephthaloyl chloride showed that as the mole fraction of 2,4‐DABN increased the initial decomposition temperature decreased, but the char yield and glass transition temperature increased gradually from the poly(1,3‐phenylene isophthalamide) to the polycyanamide homopolymer. To confirm the nucleophilic displacement reaction mechanism rather than isomerization cyclization suggested by Barashkov et al. for aramids with the cyano group ortho to the amide bond, a high‐temperature cell attached to a FT‐IR spectrometer were employed. Model compound studies also showed evidence for the benzoxazole ring formation.
Raman spectroscopic study of the effect of take‐up speed on conformation, orientation, and crystallinity in PET fibers
Authors: Bulkin Bernard J. , Deblase Frank J. , Lewin Menachem
Published: April 2003

The dependence of the Raman spectrum of PET fibers on take‐up speed (TUS) during high‐speed spinning is examined. It is found that conformational change, orientation, and crystallinity, all different functions of TUS as a processing variable, are reflected in the spectra. The data, as well as those from thermal annealing of PET fibers, are shown to be consistent with those from other techniques, leading to a set of equations from which a number of properties of the PET fibers can be determined from the Raman spectrum alone.
The thermal properties of poly(oxy‐1,4‐benzoyl), poly(oxy‐2,6‐naphthoyl), and its copolymers
Authors: Cao Mao‐Yong , Varma‐Nair Manika , Wunderlich Bernhard
Published: April 2003

The thermal properties, i.e., heat capacity, enthalpy, entropy, and Gibbs function, and the transition behavior of the copolymer system of 4‐hydroxybenzoic acid and 2,6‐hydroxynaphthoic acid have been studied based on differential scanning calorimetry. The heat capacities of the glass, crystal, and anisotropic melt are shown to be largely additive on a molar basis. Additivity is lost in the two transition regions, glass transition and disordering transition. Isothermal crystallization experiments on the copolymers revealed the existence of two types of crystals which melt at high temperature (fast‐grown crystals) and low temperature (slowly grown crystals). The ATHAS computation method is used to bring heat capacities of the solid state into agreement with approximate frequency spectra. The changes in heat capacity at the glass transitions occur at 434°K for the poly(oxy‐1,4‐benzoyl) [33.2 J/(K mol)] and at 420°K for poly(oxy‐2,6‐naphthoyl) [46.5 J/(K mol)]. The copolymers have a transition range of above 100°K. The anisotropic melt is linked to the well‐known condis state of poly(oxy‐1,4‐benzoyl) by a continuous changes in disorder and mobility without an additional first‐order transition.
Electro‐oxidative polymerization of 1,3‐Cyclohexadiene
Authors: Yamamoto Kimihisa , Asada Toshio , Nishide Hiroyuki , Tsuchida Eishun
Published: April 2003

1,3‐Cyclohexadiene is electropolymerized at a lower applied potential, compared with the polymerization of other alkene compounds, to give insoluble polymer film on an electrode. The formed polymer contains a phenylene repeated unit, which is confirmed by IR, 1H‐ and 13C‐NMR spectroscopy. Poly(cyclohexene) produced by the electropolymerization is partially aromatized by the oxidation to form a phenylene unit which is accompanied by an elimination of a proton.
ESR imaging study of the spin distribution in ladder type polymer films containing spatially selective conducting patterns
Authors: Dahm J. , Davidov D. , Macho V. , Spiess H. W. , McLean M. R. , Dalton L. R.
Published: April 2003

Stable patterns with high local electrical conductivities and different local spin densities can be created in ladder type polymer films (5–20 μm thickness) by first preheating to a temperature (Tp) followed by spatically selective laser annealing. Two dimensional images of the spin distribution in such films were determined using ESR imaging. The 2‐D images of 20 μm films exhibit peaks or dips in the spin density at the laser illuminated regions, which strongly depend on the preheating conditions. These phenomena are attributed to spin density gradients caused by a temperature gradient across the film upon illumination; it should be noted that the laser beam does not penetrate completely through such relatively thick films.
Recoverable polyimides. (II): DSC studies of copolymers from 4, 4′‐dithiodianiline bismaleimide (DTDA‐BM) and aromatic diamines
Authors: Wu Yulong , Tesoro G. C.
Published: April 2003

Interest in the recently reported polyimide resins containing disulfide bonds, which could be cleaved by reduction for reprocessing and/or recovery, prompted the present investigation of polymers and copolymers of the DTDA bismaleimide previously described. Differential scanning calorimetry (DSC) studies were carried out to identify the structures, curing conditions and modifications of reduced products of potential value for industrial applications. Results have shown that selected cured copolymers of DTDA bismaleimide with aromatic diamines can be solubilized by reduction and reset in subsequent reactions to yield thermosets of satisfactory properties.
The utilization of SANS to solve polymer latex structural problems: Basic science and engineering
Authors: Sperling L. H. , Klein A. , Yoo J. N. , Kim K. D. , Mohammadi N.
Published: April 2003

Small‐angle neutron scattering studies have been used to clarify several aspects of the internal structure of latexes and subsequent film formation modes. This paper reviews work both around the world and at Lehigh University on those subjects. Two points have been made clear: (1) The appearance of core‐shell phenomena in latexes depends on the size of the polymer chain to that of the latex particle; the phenomenon is most marked when the radius of gyration of the chain is about one fifth as big as the latex radius. (2) Strength build‐up during film formation depends on the extent of interdiffusion of the chains. For moderate molecular weights, interdiffusion distances of one radius of gyration yield maximum strength. For both moderate (250,000 g/mol) and high (2,000,000 g/mol) molecular weights, full strength was achieved in two hour's annealing time at 144°C.