bluuebunny/crossref_metadata_2025 huggingface dataset:
Isolation and cationic ring‐opening polymerization of 2,3,5,6‐tetrahydroimidazo[2,1‐b][1,3]oxazole to produce a thermally stable polyurea
Authors: Miyamoto Masatoshi , Watanabe Toshio , Kimura Yoshiharu
Published: April 2003

A bicyclic pseudourea, 2,3,5,6‐tetrahydroimidazo[2,1‐b][1,3]oxazole (1), was isolated for the first time, and its cationic and spontaneous polymerizations were examined. Both polymerizations gave poly(1,3‐imidazolidin‐2‐one‐1,3‐diylethylene) (2) in high yields. The polymer is a crystalline solid with glass transition and melting temperature of 51°C and 286°C, respectively. Thermogravimetry showed that it is stable up to 450°C under nitrogen.
A novel and convenient route to ring‐opened poly(ferrocenylsilanes) with alkoxy, aryloxy, and amino substituents at silicon
Authors: Nguyen Paul , Lough Alan J. , Manners Ian
Published: April 2003

A novel and convenient route to the first poly(ferrocenylsilanes) with alkoxy, aryloxy, and amino substituents at silicon is reported. The reaction sequence involves (i) unexpectedly facile and clean halogen replacement at the bridging atom of a readily accessible dichlorosilyl‐bridged [1]ferrocenophane by OR, OAr, and NR2 groups via reactions with aliphatic and aromatic alcohols and amines in the presence of an HCl acceptor and (ii) thermal or transition metal catalyzed ring‐opening polymerization of the new ferrocenophane.
Free radical polymerization within mesoporous zeolite channels
Authors: Ng Shau Mien , Ogino Shin‐ichi , Aida Takuzo , Koyano Keiko A. , Tatsumi Takashi
Published: April 2003

Free radical polymerization of methyl methacrylate (MMA) within the uniform channels of the mesoporous zeolite MCM‐41 proceeds at 100°C to give a high molecular weight polymer (PMMA). The formation of long‐living propagating polymer‐radicals is observed by electron paramagnetic resonance (EPR). The molecular weight of PMMA within the mesopores can be controlled over a wide range by changing the monomer‐to‐initiator mole ratio.
Synthesis of end‐functionalized (1 → 6)‐2,5‐anhydro‐D‐glucitols via anionic cyclopolymerization of 1,2:5,6‐dianhydro‐3,4‐di‐O‐methyl‐D‐mannitol for preparing graft copolymers
Authors: Satoh Toshifumi , Miura Takahiro , Hatakeyama Takeshi , Yokota Kazuaki , Kakuchi Toyoji
Published: April 2003

End‐functionalized (1→6)‐2,5‐anhydro‐3,4‐di‐O‐methyl‐D‐glucitols (3a–c) were synthesized by the anionic cyclopolymerization of 1,2:5,6‐dianhydro‐3,4‐di‐O‐methyl‐D‐mannitol (1), followed by treatment with a terminating agent such as 4‐vinylbenzyl (2a), oxetanyl (2b), and methacryloyl group (2c). The end‐functionalization proceeded in a high efficiency at 73–98%. The radical copolymerization of styrene with 3a yielded a polymer (5a) whose GPC trace exhibited a unimodal peak. 5a was polystyrene with (1→6)‐2,5‐anhydro‐3,4‐di‐O‐methyl‐D‐glucitol as pendant groups whose structure was confirmed by the 1H NMR spectrum.
Living atom transfer radical polymerization of 4‐acetoxystyrene
Authors: Gao Bo , Chen Xianyi , Iván Béla , Kops Jørgen , Batsberg Walther
Published: April 2003

Living atom transfer radical polymerization (ATRP) of 4‐acetoxystyrene (1), a protected 4‐vinylphenol, leading to poly(4‐acetoxystyrene) with well‐defined molecular weight and narrow molecular weight distribution was carried out in bulk with α,α′‐dibromoxylene(2)/CuBr/2,2‐bipyridine(bpy) as initiating system. A linear M̄n versus monomer conversion plot was found in good accordance with the theoretical line, indicating 100% initiating efficiency. The polymerization is first order in respect to monomer up to about 70% monomer conversion. Deviations from linearity at higher conversion in the first order plot are due to physical effects, i.e., to the increase of the viscosity of the reaction medium. The resulting 1‐bromo‐1‐phenylethyl‐telechelic poly(4‐acetoxystyrene) (3) is a precursor of the hydrophilic poly(4‐vinylphenol) and a potential new macroinitiator.
Computer simulation study of bulk atactic polystyrene in the vicinity of the glass transition
Authors: Lyulin Alexey V. , de Groot J.J. , Michels M.A.J.
Published: April 2003

Molecular dynamics (MD) simulations of bulk atactic polystyrene have been performed in a temperature range from 100 K to 650 K at atmospheric pressure. Local translational mobility has been investigated by measuring the mean square translational displacements of monomers. The long‐time asymptotic slope of these dependencies is 0.54 at T>Tg, showing Rouse behavior. Cross‐over from motion in the cage to Rouse like dynamics has been studied at T>Tg with a characteristic crossover time follows a power law behavior as a function of T, as predicted by mode‐coupling theory (MCT). Local orientational mobility has been studied via the orientational autocorrelation functions, ACFs, (Legendre polynomials of the first and second, order) of both the main‐chain and side‐group bonds. The relaxation times of the orientational α‐relaxation follow the same power law (γ∼2.9) as the characteristic translational diffusion time. Below T>Tg both types of dynamics are described by the same activated law. The ACFs time‐distribution functions reveal the existence of activated local rearrangements already above T>Tg.
Behavior of a nematic liquid near a grafted solid surface
Authors: Brochard‐Wyart Françoise , Ou Ramdane Olivier , Tran Yvette , Auroy Philippe
Published: April 2003

We discuss the nematic order parameter and the polymer concentration profile for a solid surface carrying grafted chains. Different regimes are found, depending upon the polymer chain length and the grafting density. These ideas are compared with experimental results obtained with polystyrene in the presence of pentylcyanobiphenyl.
Weak segregation in molten statistical copolymers
Authors: de Gennes Pierre‐Gilles
Published: April 2003

We present a qualitative argument suggesting that a statistical (AB) copolymer should display a certain form of weak segregation, with A rich and B rich regions of size comparable to the coil radius. This should occur if the Flory parameter χ is larger than unity (much larger than for the phase separation of A and B of homopolymers) in agreement with detailed calculations by Frederikson, Milner and Leibler. We achieve a certain qualitative insight for the resulting microphase.
π‐conjugated columnar polyacetylenes prepared with Rh complex catalysts
Authors: Masayoshi Tabata , Takeyuki Sone , Yasuteru Mawatari , Daigo Yonemoto , Atsushi Miyasaka , Takashi Fukushima , Yoshikazu Sadahiro
Published: April 2003

Highly stereospecific polymerization of monosubstituted acetylenes was carried out using the Rh complex, [Rh(norbornadiene)Cl]2 catalysts. The resulting polyacetylenes were characterized in detail by 1HNMR, ESR, laser Raman, diffuse reflective UV, and wide angle X‐ray diffraction methods. The data showed that the Rh complex were the preferred catalyst to selectively yield the corresponding cis‐transoid polymers even at room temperature when alcohol, triethylamine or water was used as the polymerization solvent. Additionally, the resulting cis polyacetylenes were found to have a helical form whose polymer is amorphous or composed of pseudohexagonal structures called π‐conjugated columnar as self‐assembly or super structure. Further compression of the amorphous cis polymers resulted in cis to trans isomerization at room temperature under vacuum, breaking rotationally the cis C=C bonds giving π‐radicals called solitons as the origin of a polymer magnet. On the other hand, the π‐conjugated columnar was also found to show an extremely longer wavelength absorption compared with that of the amorphous one, although the absorption maximum was shifted to a shorter wavelength when the columnar was destroyed by the compression. Therefore, the formation of the π‐conjugated columnar can be considered as a new and quite useful control method concerning color of such conjugated polymers, i.e., a new concept concerning the color of conjugated polymers.
Low molar mass poly(styrene‐co‐acrylic acid) amphiphilic block copolymers: synthesis and characterization
Authors: Karakatsanis Ekaterini , Focke Walter , Summers Gabriel
Published: April 2003

Low molar mass (∼ 4000) di‐ and triblock copolymers of styrene and tert‐butyl acrylate were synthesized by atom transfer radical polymerization (ATRP) in bulk and solution conditions. A CuBr/N, N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) catalyst system in conjunction with an alkyl‐halide initiator were used to control the synthesis of the polystyrene macroinitiator and the subsequent copolymerization with tert‐butyl acrylate. Hydrolysis of the tert‐butyl acrylate blocks to acrylic acid blocks in the presence of trifluoroacetic acid resulted in the formation of an amphiphilic block copolymer. Size exclusion chromatography (SEC) and matrix assisted laser desorption ionization ‐ time of flight ‐ mass spectrometry (MALDI‐TOF‐MS) were used to determine the molar mass and molar mass distribution of the polystyrene macroinitiators and the block copolymers. 1H NMR was used to characterize the polystyrene macroinitiators and the block copolymers, and to confirm hydrolysis of the poly(tert‐butyl acrylate) blocks to poly(acrylic acid).
Molecular characterization of functional polymers and oligomers by liquid chromatography
Authors: Trathnigg Bernd , Rappel Christina , Hoedl Renate
Published: April 2003

Different chromatographic regimes can be applied to the separation of functional polymers and oligomers: Size Exclusion Chromatography (SEC), Liquid Adsorption Chromatography (LAC), Liquid Chromatography under Critical Conditions (LCCC) and Liquid Exclusion‐Adsorption Chromatography (LEAC). All oligomers of non‐ionic surfactants can be separated to the baseline by combination of these techniques. In some cases, gradient elution is required to separate all possible homologous series.
Molecular geometry and chain entanglement: parameters for the tube model
Authors: He Tianbai , Porter Roger S.
Published: April 2003

The tube diameter in the reptation model is the distance between a given chain segment and its nearest segment in adjacent chains. This dimention is thus related to the cross‐sectional area of polymer chains and the nearest approach among chains, without effects of thermal fluctuation and steric repulsion. Prior calculated tube diameters are much larger, about 5 times, than the actual chain cross‐sectional areas. This is ascribed to the local freedom required for mutual rearrangement among neighboring chain segments. This tube diameter concept seems to us to infer a relationship to the corresponding entanglement spacing. Indeed, we report here that the critical molecular weight, Mc, for the onset of entanglements is found to be Mc = 28 A/(〈R2〉0/M), where A is the chain cross‐sectional area and 〈R2〉0 the mean‐square end‐to‐end distance of a freely jointed chain of molecular weight M. The new, computed relationship between the critical number of backbone atoms for entanglement and the chain cross‐sectional area of polymers, Nc = A0,44, is concordant with the cross‐sectional area of polymer chains being the parameter controlling the critical entanglement number of backbone atoms of flexible polymers.
Thermodynamics of homogeneous equilibrium copolymerization from the point of view of the Flory‐Huggins theory
Authors: Szymanski Ryszard
Published: April 2003

A general treatment of the thermodynamics of binary copolymerization from the point of view of the Flory‐Huggins theory is given. The relations allow one to determine, on the basis of experimental data, the thermodynamic parameters of copolymerization and the parameters of intercomponent interaction (χ). On the other hand, when these parameters are known, it is possible to predict, for any initial set of conditions, the equilibrium concentrations of comonomers and the equilibrium microstructure of a copolymer. The presented simulations indicate that positive values of interaction parameters increase the volume fractions of copolymer units in equilibrium with comonomers, in comparison to an analogous copolymerization system without intercomponent interactions.
Comment on theories of interfacial tension of polymeric interfaces
Authors: Noolandi Jaan , Chen Zheng Yu
Published: April 2003

A simple scaling argument is shown to give the correction to the interfacial tension of two infinite‐molecular‐weight immiscible homopolymers arising from the translational entropy of finite‐sized chains. It is suggested that the qualitative nature of the Flory‐Huggins model, as shown by Binder and coworkers, precludes meaningful detailed comparison of experimental data with current theoretical expressions for the interfacial tension.
Homopolymer surfactant for immiscible homopolymer blends
Authors: Noolandi Jaan
Published: April 2003

It is commonly believed that block copolymers are the only type of polymeric surfactants available for incompatible homopolymers(1). We explore the conditions for which a homopolymer will also lower the surface tension between two incompatible homopolymers by lowering the enthalpic contribution to the interfacial free energy, noting that the resulting three‐component interface will not necessarily have the same mechanical strength as a block copolymer‐homopolymer interface.
Exact distribution functions in two‐dimensional lattice polymers. Comparison with maximum entropy distributions
Authors: Poland Douglas
Published: April 2003

Toeplitz matrices are used to calculate the complete distribution functions for such quantities as the fraction of a particular conformational state and the end‐to‐end distance in 2‐dimensional lattice polymer models with a finite range of intrachain correlation. These are compared with approximate distribution functions obtained using the maximum entropy principle. The two‐parameter maximum entropy distribution (giving the exact first and second moments) in most cases gives a good approximation to the exact distribution and always gives a better approximation than a simple Gaussian approximation. We illustratesome extreme forms of the distribution functions when the intrachain interactions are either very attractive or very repulsive.
Monte Carlo simulation of pulsed laser polymerization
Authors: O'Driscoll Kenneth F. , Kuindersma Michael E.
Published: April 2003

Pulsed laser polymerization (PLP) has been simulated using a Monte Carlo procedure. From the results of numerous simulations it has been shown that the molecular weight distribution (MWD) consists primarily of two superimposed distributions. One distribution, a relatively broad background, represents the termination reactions during the dark period; the other, a rather sharply peaked distribution, represents the termination reactions occurring as a consequence of the large number of small radicals produced during the laser pulse. The postulate that the inflection point on the sharp peak can be used to calculate that the propagation rate constant was tested and found to be accurate to within 3%. The relative position of the broad and sharp distributions on the chain length scale determines the qualitative appearance of the overall MWD and is in turn governed by the rate of photoinitiation and the relative values of termination and propagation rate constants. This explains the qualitatively different shapes of MWD which have been experimentally observed. Finally, it is shown that the occurrence of chain length dependent termination reactions precludes the use of an analytical expression to deduce quantitative or qualitative information about the termination reaction from PLP data.
Brownian dynamics simulation of grafted polymer brushes
Authors: Neelov Igor M. , Binder Kurt
Published: April 2003

We present results of computer simulations by the method of Brownian dynamics of polymeric brushes attached to impenetrable planes. For testing both model and method we have used one polymer brush attached to a repulsive plane and compare some results with Monte Carlo results of Lai and Binder on the bond fluctuation model. We have also studied two polymeric brushes attached to two parallel planes at different distances between planes, and investigate the interplay between the interpenetration of the brushes and the configurational properties of the grafted chains.
Force‐length relations in deformed coils above and below the theta state. Possible bimodality in the chain distribution function
Authors: Cifra Peter , Bleha Tomáš
Published: April 2003

Stretching of flexible macromolecules by an external force, acting on the chain ends, in solvents of variable quality was simulated by the Monte Carlo method on a tetrahedral lattice. The forcelength relations and the stress‐induced changes in the population of the gauche conformers were calculated for coils in theta and athermal solvents. In poor solvents, the stretching of a collapsed coil involves a rather abrupt upturn of the force‐length curve explained as a transition of a globular coil into an extended coil. In conformity with this interpretation, a bimodal shape of the chain vector distribution function P(R) was found in the intermediate range of deformation of collapsed coils. The significance of the results to the stress‐strain behavior of networks with pronounced interaction (such as collapsed gels) are discussed.
Analyzing TREF data by stockmayer's bivariate distribution
Authors: Soares João B. P. , Hamielec Archie E.
Published: April 2003

The Stockmayer bivariate distribution is used to qualitatively and quantitatively interpret TREF (temperature rising elution fractionation) spectra of polyolefins made by multiple site type catalysts. TREF spectra simulated by the proposed method can adequately fit experimental TREF data presented in the literature and can be used to help understand the mechanism of TREF separation and the nature of multiple site types catalysts.
Free volume distributions in amorphous polymers
Authors: Chow T. S.
Published: April 2003

A new free volume distribution function for amorphous polymers is derived on the basis of a lattice model. It provides a good description of the non‐Gaussian spreading observed very recently in positron annihilation experiments. This new theory shows that the non‐Gaussian distribution is a result of the large density fluctuations of holes from their equilibrium. The Gaussian distribution is recovered in the limit of small fluctuations. The size and volume distribution of the holes is uniquely defined by two structural parameters: the energy of hole formation and the lattice volume. Our theory predicts that increases in temperature will broaden the distribution and shift its lower peak to higher free volume. Increases in pressure have the opposite effect.
Chain overlap and entanglements in dilute polymer solutions: Brownian dynamics simulation
Authors: Brostow Witold , Drewniak Marta , Medvedev Nikolai N.
Published: April 2003

We have analyzed chain conformations and the existence — or otherwise — of chain overlaps and entanglements in dilute polymer solutions (at concentrations c < C*, c* = critical concentration). The fundamental problem of existence of chain overlaps in dilute solutions is also related to the drag reduction phenomenon (DR). Some experimental results pertinent to DR are explained in terms of entanglements even for solutions at concentrations defined in ppm. We report results of Brownian dynamics simulations of polymer solutions in which the equations of motion of the chains are solved by using the Langevin equation. Chains move according to actions of a systematic frictional force and a randomly fluctuating force w(t), where t is time. In addition, a shear flow field can be introduced into the model. To evaluate the structure of polymer chains in solution we have devised a measure of interchain contacts and two different measures of entanglements. The results for c = 0.3 c* demonstrate that both chain entanglements and overlaps take place even in dilute solution. They also confirm predictions from an earlier combinatorial model.
Monte Carlo simulation of chain length distribution in radical polymerization with transfer reaction
Authors: He Junpo , Zhang Hongdong , Yang Yuliang
Published: April 2003

In this paper, the basic principle and a Monte Carlo method are described for numerically simulating the chain‐length distribution in radical polymerization with transfer reaction to monomer. The agreement between the simulated and analytical results shows that our algorithm is suitable for systems with transfer reaction. With the simulation algorithm, we confirm that transfer reaction has a similar effect as disproportionation on the molecular weight distribution in radical polymerization with continuous initiation. In the pulsed laser (PL) initiated radical polymerization with transfer reaction, the ‘waves’ on the chain‐length distribution profile become weaker as the ratio of transfer reaction rate constant, ktr, to the propagation rate constant, kp, is increased in the case with either combination‐type or disproportionation‐type termination. Moreover, it seems that the combination termination has a broadening effect on the waves. Therefore, kp can also be determined by precisely locating the inflection point Lo on the chain‐length distribution profile for radical polymerization with transfer reaction, unless ktr is large enough to smear out the waves on the chain‐length distribution.
Calculation of critical points not requiring the derivatives of the Gibbs energy demonstrated for a mixture of two homopolymers with the corresponding copolymer
Authors: Horst Roland , Wolf B. A.
Published: April 2003

The method for the calculation of phase diagrams (spinodal, binodal and tie lines) exclusively on the basis of the Gibbs energy of mixing, ΔG, with no need of calculating its derivatives with respect to the composition variables was extended to determine the critical conditions and the condition of the stability of the critical points. The method is applied to a ternary mixture of two homopolymers with a copolymer consisting of the same monomers. The sequence distribution of the copolymer is kept constant between random and purely alternating, and phase diagrams are calculated for different chemical compositions of the copolymer. Three critical lines were found within a very small interval of the copolymer composition.
Electrostatic rigidity of polyelectrolytes from reparametrization invariance
Authors: Kholodenko Arkady L. , Douglas Jack F. , Vilgis Thomas A.
Published: April 2003

The persistence length lp of a polyelectrolyte chain can be represented as lp = lO + le where lO is the bare persistence and Ie is the electrostatic contribution coming from the effects of electrostatic chain self‐interactions. Using a reparametrization‐invariant path integral model of semiflexible polymers we find that Ie depends on the ionic strength I as Ie ∼ I−1/2. This result accords with experimental observations and recent Monte Carlo simulations. Reparametrization‐invariance is apparently an essential constrainet in selecting acceptable models of semiflexible polymers.
Anisotropic fluctuations in ordered copolymer phases
Authors: Yeung Chuck , Shi An‐Chang , Noolandi Jaan , Desai Rashmi C.
Published: April 2003

The random phase approximation is reformulated to investigate the anisotropic fluctuations about an ordered polymer phase. This very general method is applied to the lamellar phase of block copolymers. The calculated anisotropic scattering intensity captures the main features observed experimentally including the secondary peaks due to fluctuations with hexagonal symmetry. We also determined the limits of metastability of the lamellar phase as well as the bending and elastic moduli of the lamellae.
From the plateau problem to periodic minimal surfaces in lipids, surfactants and diblock copolymers
Authors: Gòz̀dz̀ Wojciech , Holyst Robert
Published: April 2003

A novel method is presented for generating periodic surfaces. Such periodic surfaces appear in all systems which are characterized by internal interfaces and which additionally exhibit ordering. One example are systems of AB diblock copolymers, where the internal interfaces are formed by the chemical bonds between the A and B blocks. In these systems at least two bicontinuous phases are formed: the ordered bicontinuous double diamond phase and the gyroid phase. In these phases the ordered domains of A monomers and B monomers are separated by a periodic interface of the same symmetry as the phases themselves. Here we present a novel method for the generation of such periodic surfaces based on the simple Landau‐Ginzburg model of microemulsions. We test the method on four known minimal periodic surfaces, find two new surfaces of cubic symmetry, and show how to obtain periodic surfaces of high genus and n‐tuply continuous phases (n > 2). So far only bicontinuous (n = 2) phases have been known. We point out that the Landau model used here should be generic for all systems characterized by internal interfaces, including the diblock copolymer systems.
Postpolymerization effect on molecular weight distribution generated by pulsed laser radical polymerization
Authors: Nikitin Anatolij N.
Published: April 2003

The postpolymerization effect on molecular weight distribution (MWDs) and on the Pulsed Laser Polymerization (PLP) technique for evaluation of kinetic constants is investigated. General expressions for moments are derived for a polymerization scheme that contains the reactions of chain initiation, propagation, and termination by recombination or disproportionation, under polymerization initiation by an arbitrary sequence of radiation pulses. The results of calculation of MWDs and of the weight‐average degree of polymerization (Pw) for methyl methacrylate are presented. It is shown that the Pw value strongly depends on postpolymerization. A new method for determining the rate constants of chain propagation and chain termination from a single experiment by polymerization with packets of laser pulses is presented.
Polymer blends, copolymers and networks. Scattering properties and phase behavior
Authors: Benmouna Mustapha , Briber Robert , Hammouda Boualem
Published: April 2003

The phase behavior and scattering properties of polymer blends, copolymers and networks in solution and in bulk are examined. The theoretical framework used here is based upon the extension of the random phase approximation to polymers proposed by de Gennes and its application to chains with various architectures. The case of blends containing stiff chains is considered and the effect of nematic interaction on the phase behavior and scattering properties is discussed. The compressibility problem is reviewed in connection with the free volume theory models. The coupling between density and composition fluctuations is examined together with the effects of pressure on the structural and thermodynamic properties of blends. The dynamics of copolymers are also examined in the light of the new developments both from the theoretical and experimental fronts. The extent to which the chain architecture affects phase behavior, static scattering and dynamic behavior is discussed. A particular emphasis is put on the case of cyclichomopolymers and copolymers. Free chains in a network and crosslinked blends are also a subject of particular interest in this paper. The interplay between macrophase and microphase transitions due to the crosslinks and the electrostatic forces for charged polymers is also considered. De Gennes' analogy betwen the elastic restoring forces in the network and the Coulomb forces in the dielectric medium is generalized by including the screening phenomenon. This generalization is required in order to account for the experimental observations in the low momentum transfer range. Following Briber et al., it is argued that the new screening length can be related to the initial fluctuations at the temperature of crosslinking.
Langevin dynamics simulations of macromolecules on parallel computers
Authors: Jung Bernd , Lenhof Hans‐Peter , Müller Peter , Rüb Christine
Published: April 2003

A parallel algorithm is developed that allows efficient Langevin‐dynamics simulations of macromolecular coils, which is the usual structure of synthetic polymers in solution and in bulk. Contrary to usual so‐called spatial decomposition algorithms, we map the one‐dimensional topology of the chain molecule on the parallel computer. The speedup of the algorithm is measured on different multi‐processor systems. The reliability of the parallel calculations is shown by comparison with sequential simulations.
Statistical derivation of kinetic molecular weight development equations in nonlinear free‐radical polymerization
Authors: Tobita Hidetaka
Published: April 2003

We propose a statistical method to derive the differential equations that describe the weight‐average molecular weight development during nonlinear free‐radical polymerizations, by using the random sampling technique. We consider two types of nonlinear free‐radical polymerization schemes, free‐radical polymerization with chain transfer to polymer and free‐radical crosslinking (co)polymerization. The obtained equations fully agree with those obtained through the kinetic approach using the method of moments. The physical meaning of each term in the differential equations as well as the implication of the functional form is discussed from the point of view of the statistical derivation.
A theoretical approach to the thermochemistry of the polymerization of some derivatives of the monomers CH2X (X = CH2, NH, O)
Authors: Leroy Georges , Dewispelaere Jean‐Pierre , Wilante Claude , Benkadour Hanan
Published: April 2003

In this work, we have calculated the thermodynamic parameters of the polymerization of some derivatives of the species CH2X (X = CH2, NH, O), using ab initio methods of quantum chemistry and the usual formalism of statistical thermodynamics. It is shown that the Gibbs functions ΔG(l, c) corresponding to CH2NOCH3, CNCHNCN, CF2O and all the percyano derivatives are largely positive which indicates that the spontaneous (radical or ionic) chain polymerization of these monomers is thermodynamically prohibited.
Molecular weight distribution of metallocene polymerization with long chain branching using a binary catalyst system
Authors: Zhu Shiping , Li Dean
Published: April 2003

In metallocene polymerization, termination by β‐hydride elimination generates polymer chains containing unsaturated vinyl groups at their chain ends. Further polymerization of these macromonomers produces branched polymers. Material properties of the branched polymers not only depend on molecular weight and branching density, but also on chain structure. This work presents analytical expressions to predict the bivariate distribution of molecular weight and branching density for polymer chains having dendritic and comb structures. It is shown that when a single metallocene catalyst is used the formation of dendritic polymers is favored with only a very small fraction of highly branched chains assuming comb structure. The use of a binary catalyst system is therefore proposed to obtain high content of comb polymers. One catalyst generates macromonomers and the other yields in‐situ branching. It is found that the comb polymers give much narrower molecular weight distributions than dendritic polymers with same branching densities.
Protruding chain at a sharp penetrable interface
Authors: Cifra Peter
Published: April 2003

A single protruding chain at a sharp discontinuity of the quality of the surrounding medium was shown by Monte Carlo (MC) simulations to be a good model representing semiquantitatively the major macroscopic features of polymer interfaces such as the interface thickness. This is in accord with early original theoretical suggestions. Compared to multichain simulations of a polymer/polymer interface it is clear that the protruding chain is not completely adequate to represent a diffuse multichain interface. The results on a protruding chain, however, indicate the proper interfacial thickness as obtained by MC simulations in multichain systems. The microscopic results (such as deformation, orientation of coils at the interface and chain end segregation into the interface) are similar to those obtained in multichain polymer interfaces. None of the investigated interface properties exhibits a dependence on the total chain length of the protruding chain.
The effect of tethered polymers on the conformation of a lipid membrane
Authors: Birshtein Tatiana M. , Zhulina Ekaterina B.
Published: April 2003

We consider the effect of tethered macromolecules on the stability of the flat conformation of a lipid bilayer in a dense brush regime when anchored chains are significantly overlapped. On the basis of a scaling approach we have shown that redistribution of polymer chains from inner to outer layers reduces the free energy of the system and stabilizes spherically bent configurations of the membrane.
Flavonoids: Promising anticancer agents
Authors: Ren Wenying , Qiao Zhenhua , Wang Hongwei , Zhu Lei , Zhang Li
Published: April 2003

Flavonoids are polyphenolic compounds that are ubiquitously in plants. They have been shown to possess a variety of biological activities at nontoxic concentrations in organisms. The role of dietary flavonoids in cancer prevention is widely discussed. Compelling data from laboratory studies, epidemiological investigations, and human clinical trials indicate that flavonoids have important effects on cancer chemoprevention and chemotherapy. Many mechanisms of action have been identified, including carcinogen inactivation, antiproliferation, cell cycle arrest, induction of apoptosis and differentiation, inhibition of angiogenesis, antioxidation and reversal of multidrug resistance or a combination of these mechanisms. Based on these results, flavonoids may be promising anticancer agents. © 2003 Wiley Periodicals, Inc. Med Res Rev, 23, No. 4, 519–534, 2003
Genetic variability: The key problem in the prevention and therapy of RNA‐based virus infections
Authors: Figlerowicz Magdalena , Alejska Magdalena , Kurzyńska‐Kokorniak Anna , Figlerowicz Marek
Published: April 2003

Despite extraordinary progress that has recently been made in biomedical sciences, viral infectious diseases still remain one of the most serious world health problems. Among the different types of viruses, those using RNA as their genetic material (RNA viruses and retroviruses) are especially dangerous. At present there is no medicine allowing an effective treatment of RNA‐based virus infections. Many RNA viruses and retroviruses need only a few weeks to escape immune response or to produce drug‐resistant mutants. This seems to be the obvious consequence of the unusual genetic variability of RNA‐based viruses. An individual virus does not form a homogenous population but rather a set of similar but not identical variants. In consequence, RNA‐based viruses can easily adapt to environmental changes, also those resulting from immune system response or therapy. The modifications identified within viral genes can be divided into two groups: point mutations and complex genome rearrangements. The former arises mainly during error‐prone replication, whereas RNA recombination and generic reassortment are responsible for the latter. This article shortly describes major strategies used to control virus infections. Then, it presents the various mechanisms generating the genetic diversity of RNA‐based viruses, which are most probably the main cause of clinical problems. © 2003 Wiley Periodicals, Inc. Med Res Rev, 23, No. 4, 488–518, 2003
Beneficial effects of creatine supplementation in dystrophic patients
Authors: Louis Magali , Lebacq Jean , Poortmans Jacques R. , Belpaire‐Dethiou Marie‐Claude , Devogelaer Jean‐Pierre , Van Hecke Paul , Goubel Francis , Francaux Marc
Published: April 2003

The effect of creatine (Cr) supplementation on muscle function and body composition of 12 boys with Duchenne muscular dystrophy and three with Becker dystrophy was evaluated by a randomized double‐blind cross‐over study (3 g Cr or maltodextrin daily for 3 months, with wash‐out period of 2 months). After placebo, no change was observed in maximal voluntary contraction (MVC) and resistance to fatigue, whereas total joint stiffness (TJS) was increased by ∼25% (P < 0.05). The patients receiving Cr did not show any change in TJS, improved MVC by 15% (P = 0.02), and almost doubled their resistance to fatigue (P < 0.001). In patients still independent of a wheelchair (n = 5), bone mineral density increased by 3% (P < 0.05), and urinary excretion of collagen type I cross‐linking N‐telopeptide declined to about one third (P < 0.001) after Cr. No adverse effect was observed. Thus, Cr may provide some symptomatic benefit in these patients. Muscle Nerve 27: 604–610, 2003
Polymer blends containing liquid crystal polymers
Authors: Ballauff Matthias
Published: April 2003

Polymer blends can be either composed of mixtures of flexible components, of a stiff chain and a flexible macromolecule, or of two stiff‐chain polymers. All three cases may be dealt with in terms of the Flory lattice model. Special attention is paid to the influence of liquid crystalline order on the miscibility of the two polymers. For isotropic mixtures all three cases may be described in terms of the usual Flory–Huggins approximation. If a nematic phase is formed the miscibility of blends of rigid rods with flexible macromolecules (molecular composites) is strongly reduced because of entropic reasons. Highly ordered mixture of two stiff‐chain polymers in melt can be described in terms of the regular solution theory leading to the same miscibility criterion as is valid for two flexible polymers. All deductions are compared to recent experimental work.
Preparation of polyimides utilizing the diels–alder reaction. I. Bis(3,4‐dimethylenepyrrolidyl) arylenes with bismaleimides
Authors: Ottenbrite Raphael M. , Yoshimatsu Akira , Smith Joseph G.
Published: April 2003

Bis(exocyclic)dienes were prepared by the reaction of 2,3‐dibromomethyl‐1,3‐butadiene with aromatic diamines. The diamines were 4,4′‐methylene dianiline, 4,4′‐oxy dianiline, benzidine, and α, α′‐bis(4‐aminophenyl)‐p‐isopropyl benzene (EPON HPT 1061). Polymers were synthesized by the Diels–Alder reaction of these bisdienes with bis(4‐maleimidylphenyl) methane. Flexible films were obtained for diene: dienophile ratios ranging from 0.7 : 1 to 0.8 : 1. Films were found to be insoluble in organic solvents and those cured above 120°C were insoluble in concentrated sulfuric acid. The polymers were characterized by IR, TGA, and elemental analysis.
Thermal and nuclear magnetic relaxation studies of water–sodium polystyrene sulfonate systems
Authors: Hatakeyama T. , Hatakeyama H.
Published: April 2003

The phase transition behavior of water–sodium polystyrene sulfonate (NaPSS) systems was investigated by differential scanning calorimetry (DSC), 1H and 23Na nuclear magnetic resonance spectroscopy (NMR) in a temperature range from 150 to 330 K, and in a water content (Wc = grams of water/gram of dry sample) range from 0 to 2.5. With slow cooling from the isotropic liquid state, the system formed the liquid crystalline state and the crystalline state. The temperature range of the liquid crystalline state became broader with deceasing Wc. When the system contained an excess amount of free water, the liquid crystalline state was not observed. The 1H longitudinal relaxation time (T1) of the system showed a minimum value in the temperature range where the liquid crystalline state was observed. At the same time, the 1H transverse relaxation time (T2) dropped at the transition temperature from the isotropic liquid to the liquid crystalline state (T*). The correlation time (τc) was calculated using modified Woessner's equations. The variation of τc as a function of temperature agreed well with the phase diagram obtained from DSC. The 23Na T1 and T2 values were correlated with Wc and temperature. The activation energy was calculated to be from 20 to 25 KJ/mol depending on Wc. The formation of the liquid crystalline phase of NaPSS is affected by 10–20 water molecules, which can be categorized as freezing bound water.
Thermolysis of reactive oligo(p‐phenylene sulfide) containing disulfide bond
Authors: Oyaizu Kenichi , Katoh Junya , Suzuki Fumiaki , Jikei Mitsutoshi , Yamamoto Kimihisa , Nishide Hiroyuki , Tsuchida Eishun
Published: April 2003

Oligo(phenylene sulfide) (OPS) containing one disulfide bond at the end of the chain, which was obtained by the oxidative polymerization of diphenyl disulfide, had a relatively low Td10%(temperature for 10% weight loss) of 412 °C because of degradation of the disulfide bond. But this thermal cleavage of the disulfide bond promoted the curing reaction through thiophenoxy radical formation. OPS was allowed to react with diiodobenzene at 220 °C. The thermal stability of OPS was improved through the consumption of the disulfide bond and the coupling of the chain.
Role of solvent in the compatibility of a vinylchloride–vinylacetate–maleic acid terpolymer and nitrocellulose blends
Authors: Banerjee Amar Nath , Chattopadhyay Saumya
Published: April 2003

The compatibility of cast films of a vinylchloride–vinylacetate–maleic acid terpolymer (VMCH) and nitrocellulose (NC) blends is influenced by solvents. Transparent films of VMCH/NC blends are obtained when cast from solvents such as tetrahydrofuran or cyclohexanone, whereas hazy films are obtained when cast from solvents such as acetone or ethylacetate. Visible spectroscopy and phase morphology were used to analyse the compatibility–incompatibility of the blend. Differential scanning calorimetry (DSC) studies demonstrate that the transparent film is compatible, but the hazy film is incompatible. Fourier transform infra‐red (FTIR) studies establish that a greater interaction is observed between the polymer pair in case of the compatible blend than in the case of the incompatible blend.

A solvent dependency of blend compatibility is reflected in this study. The conformational state of the polymers in solution, which is responsible for the compatibility phenomena, may depend on the donor number and/or Taft‐β value of the solvent. The greater the donor number and/or the Taft‐β value, the higher may be the level of interaction between the solvent and the polymer molecules, which in turn may give a compatible blend after removal of the solvent.
Phase transition of layer structure of poly(1,4‐benzenedithiol‐co‐1,4‐diethynylbenzene) by photon mode
Authors: Kobayashi Eiichi , Ohashi Toyoshi , Furukawa Junji
Published: April 2003

The effect of light wavelength on the phase transition of the layer structure of poly(1,4‐benzenedithiol‐co‐1,4‐diethynylbenzene) was studied under an air atmosphere at 18–22°C. The thin layer polymer crystals were prepared by solid state polymerization, and the amount of the layer structure was evaluated by an X‐ray diagram. A monochromatic light with a wavelength in the region of ca. 500–600 nm was used as a light source. The amount of the layer structure was found to be altered by light. There were three characteristic wavelengths at 545.6, 567.8 and 590.1 nm, inducing pronounced peak intensities in the X‐ray diagram. On the other hand, at 501.1, 539.6, 571.8 and 588.1 nm the light made the peak intensity decrease steeply. The phase transition was induced by a photon mode, but not by a heat mode. The amount of the layer structure was altered linearly with increasing irradiation time up to 60 min. However, over 60 min the change became dull. The total energy given to the polymers during the irradiation was about 24 X 10−3 J/cm2. Accordingly, the phase transition occurs with a high sensitivity to the light. The polymers were irradiated alternately by the light of 545.6 nm and 571.8 nm at intervals of 60 min, respectively. The amount of the layer structure was controlled reversibly by the light.
Polarization and viscosity measurements of ferroelectric liquid crystalline monomer polymer mixtures
Authors: Bömelburg Jan , Heppke Gerd , M.‐Hollidt Jörg
Published: April 2003

Measurements of spontaneous polarization, tilt angle and response time on mixtures of a ferroelectric side chain polyacrylate with a low molecular mass liquid crystal of a very similar structure are reported. From the obtained values the rotational viscosity for the ferroelectric switching process is calculated. All mixtures exhibit an Arrhenius‐like temperature dependence of the rotational viscosity, the values for the polymer being three orders of magnitude higher than for the low molecular mass compound.
Controlled release of 4‐hydroperoxycyclophosphamide from the fatty acid dimer‐sebacic acid copolymer
Authors: Buahin Kwame G. , Judy Kevin D. , Hartke Carol , Domb Abraham J. , Maniar Manoj , Colvin O. Michael , Brem Henry
Published: April 2003

Controlled polymeric release of chemotherapeutic agents has shown promise in the management of malignant gliomas. 4‐Hydroperoxycyclophosphamide (4HC), loaded on the fatty acid dimer–sebacic acid copolymer (FAD:SA, 1:1), significantly prolonged survival in rats implanted with F98 and 9L gliomas. Here, we studied the in vitro and in vivo release kinetics in phosphate‐buffered saline and rat brain of 20% 4HC/FAD:SA (wt:wt), the optimal dose for treatment of rat gliomas. In vitro release under infinite sink conditions was steady over the initial 12 hr to a peak of 20–35% of impregnated drug, consistent with early phase control via surface erosion. Release over the next 3 weeks was minimal, consistent with barrier formation around the polymer by an oily fatty acid dimer degradation product and consequent slowing of release. However, the polymer started to disintegrate by day 4, and there were minimal visible remnants by 3 weeks. Thus, a considerable amount of polymer‐carried drug was probably lost in the disintegrating fragments. Also, drug loss is expected from its inherent hydrolytic instability. In vivo release into brain revealed two peak levels of drug at 0–1 hr and 5–20 days. With loaded polymer implanted intraperitoneally or cyclophosphamide injected systemically, peak brain drug levels were measured in 2–8 hr, with substantial decrease by 48 hr without a second peak. Brain levels were substantially higher than blood levels at all time periods. We conclude that FAD:SA (1:1) adequately protects the otherwise labile 4HC, allowing effective and substained drug release in vivo. Furthermore, it should be possible to modify the polymer to adjust the time of peak release for more beneficial therapeutic effects.
Poly(benzylsulfonic acid) siloxane as proton‐conducting electrolyte
Authors: Sanchez J.‐Y. , Denoyelle A. , Poinsignon C.
Published: April 2003

A new proton‐conducting polymer electrolyte—poly‐(benzylsulfonic acid)siloxane (PBSS)—has been prepared by sol–gel process. Both the hydrolysis and the condensation reactions of triethoxybenzylsilane have been studied under different catalysis conditions. The basic material—polybenzylsiloxane (PBS)—is always soluble, no matter what the experimental conditions, reaching an average molecular weight—Mw—of 20,000 and a polydispersity index close to 5. Good yields of a water‐soluble polyelectrolyte—PBSS–thermally stable up to 300°C in air according to thermogravimetric analysis (TGA), and for which the exchange capacity is close to 4.4, can be obtained by sulfonation of PBS. Conductivities ranging from 2 × 10−3 to 10−2 S/cm at room temperature have been determined by a.c. impedance spectroscopy. These high conductivities, as well as the tensile strength of the PBSS, allow its use in several electrochemical devices.