bluuebunny/crossref_metadata_2025 huggingface dataset:
Topological polymer chemistry: classification and construction of nonlinear polymer architectures
Authors: Tezuka Yasuyuki
Published: April 2003

A systematic classification of nonlinear polymer architectures is formulated by reference to constitutional isomerism in a series of alkanes (CnH2n+2), monocycloalkanes (CnH2n) and polycycloalkanes (CnH2n−2, CnH2n−4, etc). And a variety of topologically unique polymers, such as monocyclic and polycyclic polymers, cyclic telechelics (kyklo‐telechelics), cyclic macromonomers and polymeric topological isomers have been constructed by means of an “electrostatic self‐assembly and covalent fixation” strategy. In this process, new telechelic polymer precursors having moderately strained cyclic onium salt groups carrying multifunctional carboxylate counteranions have been prepared as key polymer precursors. The unique electrostatic self‐assembly, formed particularly in a dilute solution, was covalently fixed through the ring‐opening reaction by heating, to produce a variety of nonlinear polymer architectures in high efficiency.
Fluorescence study for the electrostatic interaction and aggregation in dilute polar solution of polyelectrolytes
Authors: Sun Qilong , Ren Biye , Liu Xinxing , Zeng Fang , Liu Ping , Tong Zhen
Published: April 2003

Fluorescence decay and quenching of pyrene labels on copolymers of 2‐acrylamido‐2‐methylpropanesulphonic acid (AMPS) and N,N‐dimethylacryl‐amide (DMAA) were observed in dilute salt‐free aqueous solutions as a function of the mole fraction FAMPS of AMPS from 0 to 0.896. Monoexponential and biexponential decays were found for the samples of FAMPS < 0.35 and samples of FAMPS > 0.35, respectively. The fast decay component is 80% and the averaged lifetime <τ> and lifetime τ1 of the fast decay decreased with increasing FAMPS. Quenching efficiency of Cu2+, CH3NO2, and dinitrobenzene to the pyrene label was investigated in the framework of Stern‐Volmer plot. The quenching effects of Cu2+ included both of dynamic and static ones, the latter was due to the condensed Cu2+. For the neutral quenchers, the quenching rate constant kq increased when FAMPS < 0.449 then decreased, showing a decline of accessibility to the pyrene label. I1/I3 value in salt‐free dilute aqueous solution and in DMSO solution decreased obviously with an increase in FAMPS, indicating that the labeled fluorophore experienced a decrease in polarity of its microenvironment with increasing charge density of the polymer. This I1/I3 decrease was enhanced with increasing the polymer concentration and adding salt NaCl up to 0.75 mol/L showed no effect on the appearance of this decrease. These results were interpreted consistently with the counterion condensation concept, where condensed counterions induced the “temporal” aggregation of less‐polar in the polyelectrolyte solutions surrounding the pyrene labels.
Living ring‐opening polymerization of cyclic thiocarbonate
Authors: Endo Takeshi , Nemoto Nobukatsu , Sanda Fumio
Published: April 2003

This work deals with the cationic ring‐opening polymerization of a cyclic thiocarbonate, 5,5‐dimethyl‐1,3‐dioxane‐2‐thione (1). The polymerization was carried out with 2 mol% of trifluoromethanesulfonic acid, methyl trifluoromethanesulfonate, boron trifluoride etherate, or triethyloxonium tetrafluoroborate as an initiator to afford the polythiocarbonate with the narrow molecular weight distribution (Mn = 11200‐31000, Mw/Mn = 1.04‐1.15). The molecular weight of the obtained polymer could be controlled by the feed ratio of the monomer to the initiator and increased when the second monomer was added to the polymerization mixture after quantitative consumption of 1 in the first stage, supporting that the cationic ring‐opening polymerization of 1 proceeded via a living process.
Synthesis of branched polymers by means of anionic polymerization. 11. anionic synthesis of densely branched polystyrenes carrying double branches in each repeating unit
Authors: Hirao Akira , Ryu Sang Wong
Published: April 2003

We have demonstrated the first successful synthesis of well‐defined densely branched polystyrenes carrying double branches in each of all repeating unit of backbone polymer by the coupling reaction of 1,1‐diphenylethylene‐end‐capped polystyryllithiums with novel polystyrene derivatives having two benzyl bromide moieties in each monomer unit. The coupling reaction efficiently and quantitatively proceeded without any steric limitations to introduce two polystyrene branches in each repeating unit under certain conditions in THF at −40°C. Thus, a series of 36.4‐ and 181‐arm densely branched polystyrenes were synthesized (Mw = 365 ∼ 2 000 kg/mol, Mw/Mn = 1.01 ∼ 1.03). In the 36.4‐arm branched polystyrenes thus synthesized, the maximum Mw value of the introduced polystyrene as a branch segment was 55.1 kg/mol. The experimental g‘ values of the 36.4‐arm branched polystyrenes deterimined in the range of 0.14 ∼ 0.15 were very close to the value of 0.13 calculated from the empirical equation previously reported by Roovers.
Approaches to conjugated polymers via solid state polymerization
Authors: Sandman Daniel J. , Kim Ik‐Bum , Njus Jeffrey M. , Lee Dong‐Chan , Cholli Ashok L. , Sahoo Sangrama
Published: April 2003

Topochemical solid state polymerization is a method of obtaining fully crystalline macromolecules. Herein, approaches to conjugated polymers via new solid state polymerizations and the properties of materials, especially polydiacetylenes(PDA), obtained via solid state polymerization are discussed. Our attempts to polymerize cyanoalkynes and to define the thermal reaction product of a dicyanodiazepine are presented. Certain PDA exhibit absorption, likely charge‐transfer, at energies below the exciton. Nanocrystals of PDA‐DCH react with liquid bromine to give the mixed polyacetylene PDA‐DCHBr6 whose visible spectrum exhibits structure not observed in spectra of bulk crystals of PDA‐DCHBr6. The thermochromic PDA of the dialkylurethanes of 5,7‐dodecadiyn‐1,12‐diol were studied by variable temperature solid state 13C nmr. The upfield shift of the acetylene carbons as the temperature is raised above that of the thermochromic phase transition indicates the role of mechanical strains in achieving thermochromism.
Fluorescence and biochemical characterization of glycated hemoglobin
Authors: Vigneshwaran Nadanathangam , Bijukumar Gopalakrishnapillai , Karmakar Nivedita , Anand Sneh , Misra Anoop
Published: April 2003

Isoelectric focusing (IEF) of glycated hemoglobin (GHb) was carried out in ultra‐thin polyacrylamide gels to separate the hemoglobin‐advanced glycation endproducts (Hb‐AGEs) from the hemoglobin‐A1C (HbA1C) fraction. Precast polyacrylamide gels (Ampholine® PAGplate) were used in Pharmacia LKB Multiphor II for this purpose. The separated bands for Hb‐AGE and HbA1C based on their isoelectric point (pI), were confirmed with the purifed fractions obtained from the cation exchange chromatographic technique. From the calibration curve, the pI values were found to be 6.748 and 6.495 for HbA1C and Hb‐AGE, respectively. The lowering of pI values for glycated hemoglobin, when compared to unglycated hemoglobin (pI = 6.852), can be attributed to the glycation at the amino terminals of the peptide chains. Increased reduction in pI value for Hb‐AGE can be attributed to the effect of glycation of amino groups at various sites on the peptide chains, apart from the terminal amino groups. Fluorescence analysis was carried out for the purified fraction of Hb‐AGE which showed the formation of a new fluorophor adduct having the excitation and emission maxima at 308 nm and 345 nm, respectively. Time‐dependent formation of Hb‐AGE under in vitro conditions was monitored by fluorescence (308/345 nm) over a period of 120 days, which showed its formation only after 3 weeks of incubation.
Multipolymers with Fischer‐Tropsch olefins
Authors: Tincul Ioan , Smith Jaco , van Zyl Pieter
Published: April 2003

Multipolymers consisting of ethylene, 1‐heptene, 3‐methylpentene and 4‐methylpentene were prepared with a heterogeneous Ziegler‐Natta catalyst. The polymers were prepared in such a way that the molar fraction of the comonomers remained the same. Copolymers of ethylene/1‐heptene and ethylene/4‐methylpentene were prepared in order to study the changes in polymer characteristics as one moves from an ethylene/linear alpha olefin copolymer through ethylene multipolymers to an ethylene/4‐methylpentene copolymer. The mechanical, rheological and application properties showed expected trends.
Synthesis and characterization of novel soluble and thermally stable polyamides based on pyridine monomer
Authors: Mehdipour‐Ataei Shahram , Heidari Hani
Published: April 2003

Nucleophilic aromatic substitution reaction of 4‐aminophenol and also 5‐amino‐1‐naphthol with 2,6‐dichloropyridine in N‐methyl‐2‐pyrrolidone (NMP) as solvent, in the presence of potassium carbonate, afforded two aromatic ether diamines. Eight soluble, thermally stable polyamides were prepared by polycondensation reaction of the obtained diamines with aromatic and aliphatic diacid chlorides including terephthaloyl chloride (TPC), isophthaloyl chloride (IPC), adipoyl chloride (AC), and sebacoyl chloride (SC). The prepared monomers and polymers were characterized by conventional spectroscopic methods. Physical and thermal properties of the polymers, such as thermal behavior, thermal stability, solution viscosity, and solubility behavior were also studied.
New materials by polymerisation of olefins and styrene with metallocene catalysts
Authors: Kaminsky Walter , Tran Phu‐Dennis , Weingarten Ulrich
Published: April 2003

Metallocenes are highly active catalysts for the production of precisely designed polyolefins and engineering plastics. Especially zirconocene/methylalumoxane (MAO) catalysts and half‐sandwich titanium complexes have opened a frontier in the area of new polymer synthesis and processing. The materials obtained show different microstructures, tacticities and properties compared with conventional polymers. Alternating ethene/propene polymers show lower glass transition temperatures than random copolymers. Constrained geometry catalysts are useful for the synthesis of norbornene/ethene copolymers.
Copper‐mediated ATRP of methyl methacrylate in polar solvents using a bifunctional pyridinal diimine ligand
Authors: Iovu Mihaela , Maithufi Norah , Mapolie Selwyn
Published: April 2003

The bifunctional pyridinal diimine ligand, bis(2‐pyridinal)ethylenediimine, was employed in copper‐mediated ATRP of methylmethacrylate using solvents such as acetonitrile, N,N‐dimethyl formamide and dimethylsulfoxide. Solvent polarity was found to play a crucial role in determining the extent of control in the ATRP process. Acetonitrile showed the best control when used at a level of 33 vol.‐%.
The synthesis of HgS and CdS nanoparticles in polymer matrices
Authors: Sreekumari Nair P. , Radhakrishnan T. , Revaprasadu N.
Published: April 2003

The synthesis of CdS nanoparticles in two different polymer matrices ie. polyacrylamide and polystyrene, is described. In addition, we describe the synthesis of HgS nanoparticles in polyacrylamide. Both the CdS and HgS nanocomposites show blue shifts in the optical spectra in relation to the bulk material. The photoluminescence spectra of both materials show broad emission. The transmission electron microscopy (TEM) images confirm the nanocrystalline nature of the CdS and HgS nanocomposites.
The use of selected acrylate and acrylamide‐based surfmers and polysoaps in the emulsion polymerization of styrene
Authors: Tichagwa Lilian , Götz Christian , Tonge Matthew , Sanderson Ron , Pasch Harald
Published: April 2003

Polymerizable surfactants (surfmers) 12‐acryloyloxy‐dodecanoic acid and 11‐acrylamidoundecanoic acid and their respective sodium salts were prepared and then polymerized to form their corresponding oligomers using reversible addition‐fragmentation chain transfer (RAFT). Different concentrations of both the surfmers, their sodium salts, and their RAFT oligomers were used as polysoaps in the emulsion polymerization of styrene. Stabilities of the pre‐emulsions before polymerization were determined and compared. After polymerization, particle sizes and polydispersities of the resulting polystyrene latices were determined. Sodium dodecyl sulfate (SDS) was used as a reference surfactant to compare the particle sizes and stabilities of the pre‐emulsions prepared using surfmers and polymeric surfactants (polysoaps) as particle stabilizers.

Emulsion polymerization of styrene using these surfmers and polysoaps all led to latices which were stable for a period of more than six months, as indicated by constant particle sizes, whereas latices prepared using the conventional surfactant, SDS, were not as stable.
Study of a new route by which to make fully cured thermoplastic elastomers with plastics and ultrafine powdered rubber
Authors: Zhang Xiaohong , Wei Genshuan , Liu Yiqun , Gao Jianming , Zhu Yicai , Song Zhihai , Huang Fan , Zhang Manli , Qiao Jinliang
Published: April 2003

A series of fully cured thermoplastic elastomers (TPEs) have been developed by mixing plastics and fully cured, ultra‐fine powdered rubbers (UFPRs). The fully cured UFPRs were prepared by the irradiation of rubber latexes and drying of the irradiated rubber latexes. The average particle size of the UFPRs ranged from 50 to 500nm. The influences of the dose rate, absorbed dose and content of cross‐linking agent on the cross‐linking of rubber latexes were studied. It was found that a new type of TPEs with excellent properties can be easily made by blending UFPRs with plastics.
Recent advances in the development of Fischer‐Tropsch catalysts at sasol
Authors: Bromfield Tracy C. , Vosloo Anton C.
Published: April 2003

Sasol's experience of more than 50 years in the field of Fischer‐Tropsch puts it in a unique position to exploit the renewed interest in the utilization of the Fischer‐Tropsch process to convert natural gas to liquids. In order to capitalize on this position, Sasol has made significant improvements to its low temperature and high temperature Fischer‐Tropsch catalysts. A review is given of the development of Sasol's Co‐based catalyst for low temperature Fischer‐Tropsch applications. Sasol has also developed a new Fe‐based catalyst for the high temperature Fischer‐Tropsch process. The advantages of this catalyst compared to the existing catalyst are discussed.
Monitoring thermo‐oxidative degradation of polypropylene by CRYSTAF and SEC‐FTIR
Authors: de Goede Stefan , Brüll Robert , Pasch Harald , Marshall Niall
Published: April 2003

Samples of a polypropylene homopolymer have been degraded and analysed with regard to chemical composition, molecular weight distribution and chemical composition distribution. FTIR shows the progress of degradation and a decrease in molecular weight can be observed from SEC. CRYSTAF shows that the chemical heterogeneity of the samples broadens with continuing degradation. SEC‐FTIR reveals that the degraded species are mainly found in the low molecular end of the molecular weight distribution. The spatial heterogeneity of the degradation process has been proven by the analysis of abrased layers.
Kinetic evaluation of various isospecific active sites on MgCl2‐supported Ziegler catalysts
Authors: Nishiyama Isa , Liu Boping , Matsuoka Hitoshi , Nakatani Hisayuki , Terano Minoru
Published: April 2003

The formation, variation and conversion of isospecific active sites were investigated, based on the isotacticity distribution of the polypropenes analyzed by the temperature rising elution fractionation (TREF) method. Stopped‐flow polymerization of propene was carried out with a MgCl2‐supported Ziegler catalyst in the absence or presence of an internal or external electron donor so that the effects and roles of the electron donors could be clarified. The results showed that various kinds of active sites with different isospecificities, including the highest isospecific active sites responsible for producing the highest isotactic fraction (elution temperature: > 112°C) existed, even in the electron donor‐free catalyst system. The isospecificity of the active sites in the donor‐free catalyst might have originated from a surface monolayer multinuclear titanium species, namely an “island” of titanium species. The addition of the external electron donor converted a part of the aspecific and/or low isospecific active sites into the second highest isospecific active sites, but showed no effect on the formation of the highest isospecific active sites, whereas the addition of an internal donor played an important role in creating the highest isospecific active sites as well as suppressing the formation of the aspecific active sites.
Toughening polypropylene with nanoscale rubber particles
Authors: Liu Yiqun , Zhang Manli , Zhang Xiaohong , Gao Jianming , Wei Genshuan , Huang Fan , Song Zhihai , Qiao Jinliang
Published: April 2003

A new kind of powdered rubber, ultra‐fine full‐vulcanized powdered rubber (UFPR), was invented and used for toughening polypropylene. The UFPR dispersed well in the PP matrix on a nanoscale. Both toughness and stiffness of PP can be improved by toughening with UFPR. DSC data showed that UFPR has some nucleation effect on PP. When PP was toughened with UFPR and EPDM together, the impact strength showed a synergistic toughening effect.
Characterization of epoxy prepreg SPX 8800 system by isothermal differential scanning calorimetry
Authors: Wang Qian , Storm Birgit K.
Published: April 2003

Isothermal Differential Scanning Calorimetry (DSC) was used to study the curing behavior of epoxy prepreg SPX 8800 system, which contains DGEBA/DICY/Diuron (Diglycidyl ether of bisphenol A/Dicyandiamide/Diuron) reinforced by three layers of glass fibre. The rate curves from the DSC study agreed well with those obtained from the isothermal FT Near Infrared (FTNIR) study and similar activation energy was obtained in the range of 92.6 to 87.7 kJ/mol up to 50% total conversion. Modelling of the whole DSC trace with empirical equation dx/dt=kxm(A‐x)n gave relatively good fitting of the experimental curves (the error is lower than 15%.) in the whole studied cure temperature range (75‐110°C) and no significant difference in cure kinetics was observed for both epoxy prepreg and neat resin.
The site of radical attack at the furan ring from MNDO calculations
Authors: Paz José A. , Vega Rebeca , Rieumont Jacques , Montero Luis A. , Alvarez J. Raul
Published: April 2003

The semi‐empirical SCF MNDO method has been used to calculate the radical reactivities for each reaction site in some neutral furan molecules as the average of the HOMO and LUMO probabilities both in 2pz atomic orbitals1

SCF: Self‐consistent field; MNDO: modified neglect of differential overlap; HOMO: highest occupied molecular orbital; LUMO: lowest unoccupied molecular orbital.

. The carbon atoms C5 and C2 of of the furan ring are the most favoured sites except for the furan derivatives holding a double bond in the substituent group. Also the SOMO2

SOMO: Single occupied molecular orbital.

probabilities of the radicals formed by addition of a hydrogen atom or a vinyl acetate model radical were calculated. Thus, once a radical is added to the C5 position the resulting radical can be partially localized on the carbon C2. Furthermore, the enthalpy of reaction for several radicals was estimated by using the calculated heats of formation of the neutral furan molecules and their radicals. The radical addition to the carbon C 5 resulted in the most exothermic reaction in comparison with other reaction sites of the molecule. However, no correlation was found between the calculated enthalpies and the degradative‐transfer kinetic constants experimentally determined for the radical polymerization of vinyl acetate in the presence of the furan compounds under study.
Kinetic theory of anionic copolymerization with constant monomer ratio, 2 . Molecular weight distribution
Authors: Hu Xiaodong , Yan Deyue , Feng Jing
Published: April 2003

The kinetic differential equations for the anionic copolymerization with constant monomer ratio are treated by Laplace transformation and a graphical technique. A theoretical method is established by which all molecular parameters of the copolymers, such as the molecular distribution (MWD), the average molecular weight and the polydispersity, can be calculated from reaction rate constants, initial conditions and polymerization time. Three‐dimensional plots obtained by numerical computation are presented to illustrate the influence of the reaction conditions on the MWD's of the copolymers.
Thermodynamics of mixing of ethylene oxide oligomers with different end groups in tetrachloromethane: theoretical treatment
Authors: Killmann Erwin , Cordt Frank , Möller Friedrich
Published: April 2003

In a previous paper we reported the enthalpies of mixing of oligomers of ethylene oxide with different end groups in tetrachloromethane. This paper shows the applicability of the modified theoretical treatment, based on a quasichemical equilibrium of the contacting segmental surfaces originated from Huggins, to our experimental results. The experimental data of ethylene oxide oligomers with methoxy end groups can be described with the energy parameter Δεαβ, the equilibrium constant Kαβ and the surface ratio rσ assuming a chemically uniform surface of the oligomer in CCI4. Ethylene oxides with strong polar OH end groups can be treated successfully with an extended version of the theory with two additional parameters K and ΔΔε for systems containing three different kinds of chemical units.
Theoretical study of chain transfer in anionic polymerization. Transfer by the mechanism of side‐group substitution
Authors: Litvinenko Galina I. , Arest‐Yakubovich Alexander A.
Published: April 2003

A new theoretical consideration of chain transfer to monomer in the anionic polymerization of hydrocarbon monomers is presented. It is shown that the kinetic scheme used in theoretical studies reported previously contradicts the widespread views on the chemical mechanism of carbanionic reactions. It is suggested that the most probable path of the transfer reaction is the proton abstraction from the side group of the monomer; the terminal double bond of the monomer molecule remains unchanged, and therefore the intermediate species can participate in succeeding reactions as a macromonomer. The molecular characteristics of polymer formed in processes with monomer transfer by side‐group substitution are determined. At high conversion, the polymer formed in such a process is shown to possess a number‐average degree of polymerization, P̄n, approaching the theoretical value for living polymers, and a P̄w exceeding it the more the higher the intensity of transfer. Furthermore, it shows a broad molecular weight distribution and a fairly noticeable degree of branching. These results considerably differ from those previously reported.
Dynamics of multicomponent polymer mixtures: theoretical models
Authors: Benmouna Mustapha , Vilgis Thomas A. , Benoit Henri
Published: April 2003

Theoretical models describing the dynamics of multicomponent polymer mixtures are reviewed. Some detailed derivations are shown to make the basic assumptions clear and to ease the comparison between these models. The effects of random noise and memory functions on the time evolution of dynamical correlation functions are examined. The long‐range hydrodynamic interactions or mode‐coupling effects are also included. A possible extension of these models to the kinetics of spinodal decomposition in solutions of polymer mixtures is briefly discussed.
Multicomponent analysis of poly(propylene) using fractionation, tacticity and molecular weight data
Authors: Cheng H. N.
Published: April 2003

Heterogeneous Ziegler‐Natta catalysts are known to contain multiple catalytic sites and produce polymers that contain multiple components. An approach is described in this work that combines fractionation, 13C NMR and molecular weight distribution data to determine the number and the characteristics of the different components found in the polymer. The methodology is applied to published data on poly(propylene). The analyses indicate that poly(propylene) made with heterogeneous Ziegler‐Natta catalysts consists of at least four components. Three of these components obey enantiomorphic‐site models, and the fourth component obeys Bernoullian model.
Anisotropy of local relaxation properties of macromolecules. Polarized luminescence
Authors: Gotlib Yuli Ya. , Neelov Igor M. , Torchinski Isaak A. , Shevelev Vladimir A.
Published: April 2003

A tetrahedral lattice model for a polymer chain with three‐unit kinetic elements was used to find the correlation functions which describe the local dynamics of unit vectors oriented in the longitudinal or transverse directions with respect to the chain. These unit vectors can represent the dynamics of the emitting oscillator of the marker. It is shown that the spectra for longitudinal and transverse components of the emitting oscillator differ greatly. It is also shown that at short relaxation times the anisotropy of local relaxation properties of a kinetic chain fragment may be described by an equivalent ellipsoid with an axes ratio of ca. 10.
Anisotropy of local relaxation properties of macromolecules. Spin‐lattice relaxation of 13C nuclei, the nuclear overhauser effect and the estimation of parameters of an equivalent ellipsoid for kinetic segments of polymer chains
Authors: Gotlib Yuli Ya. , Torchinski Isaak A. , Shevelev Vladimir A.
Published: April 2003

The expressions for the functions of spectral density at different orientations of the components of the internuclear vector with respect to the chain backbone, the frequency dependences of the spin‐lattice relaxation time of 13C nuclei (T1C) and the values of the nuclear Overhauser effect (NOE) were obtained for the tetrahedral lattice model of a polymer chain with three‐unit kinetic elements. It was shown that peculiar features of the behavior of T1C and NOE reflect the characteristic properties of the spectra of relaxation (correlation) times for “longitudinal” and “transverse” components of the internuclear vector. It was established that in the range of relatively short times of the relaxation spectrum the dynamics of an anisotropic kinetic segment of the chain may be described with the aid of a simple model of an elongated ellipsoid of rotation with an axial ratio of about 10. It is shown that the equivalent‐ellipsoid model leads to significant differences from a more specific model of chain dynamics when a broad frequency range is considered.
Conformational structure of liquid‐crystalline polyesters with mesogens and spacers in the main chain
Authors: Shilov Sergei , Birshtein Tatiana , Volchek Boris
Published: April 2003

The conformations of thermotropic polyesters with alternating mesogens and poly(methylene) spacers in the main chain were investigated by conformational calculations using the data of linear‐dichroism IR‐spectroscopy, X‐ray analysis and differential scanning calorimetry. The conformations of monomeric units and of the macromolecules as a whole in different phase‐aggregated states were estimated. It is shown that in the liquid‐crystalline (LC) state the polymer chains are strongly extended. The results are compared with the data of various theories of LC ordering.
Melting point depression and phase behavior of poly(ether‐sulfone) and poly(ethylene oxide) blends: Equation‐of‐state theory approach
Authors: Kwon Ick Hwan , Jo Won Ho
Published: April 2003

Melting‐point depression in miscible polymer blends is interpreted with Flory‐Prigogine's equation‐of‐state theory (FP theory) and Sanchez‐Lacombe's lattice fluid theory (LF theory). The equations for equilibrium melting point depression in polymer mixtures are proposed from both the FP and LF theories. For miscible poly(ether‐sulfone) (PES)/poly(ethylene oxide) (PEO) blends, the proposed equations are tested. The interaction parameters, X12 in FP theory and ζ12 in LF theory, can be determined with these equations. The theoretically predicted equilibrium melting‐point depression is subdivided into three terms, namely, the equation‐of‐state, the entropy and the contact interaction terms. When the estimated interaction parameters are converted to the heat of mixing by use of both theories, the composition dependence of the heat of mixing can be properly predicted. Using the interaction parameters obtained from the melting‐point depression in PES/PEO blends, the spinodal curves are simulated from both the FP and LF theories.
Computer simulations of atomic force microscopy: crystalline polymers and the effects of surface contaminants
Authors: Sumpter Bobby G. , Getino Coral , Noid Donald W. , Wunderlich Bernhard
Published: April 2003

The atomistic dynamics of the interaction of an atomic force microscopic (AFM) probe with a crystalline polyethylene surface was examined by using the molecular dynamics method. The results show that the internal dynamics of the polymer crystal is such that rapid relaxation occurs, providing for a large amount of structural reversibility and making it possible to perform nondestructive AFM experiments. However, surface and/or AFM tip defects or contaminants (such as those which can be induced by polar molecules adsorbed on the surface), can result in significant perturbations in the AFM images produced, causing large and sharp structures to appear on the surface topology. A rationale of the mechanisms responsible for the image distortions is presented, and a relationship to defects observed in AFM and STM experiments is given.
A Monte‐Carlo study of ring formation during step‐growth polymerization in three dimensions
Authors: Fawcett Allan H. , Mee Richard A. W. , McBride Frederick V.
Published: April 2003

The formation of ring and chain molecules during an irreversible step‐growth polymerization has been modelled on a three‐dimensional twenty six choice cubic lattice, and examined by the Monte‐Carlo method. Movements were not allowed in the system in this preliminary study. The limiting value of the extent of reaction was found to be p = 0,9837 (±0,0003), and the number fraction of molecules found to be rings was 0,300 (±0,045), but the weight fraction was much smaller, 0,056 (±0,005).
Diffusion controlled copolymerization kinetics
Authors: Maxwell Ian A. , Russell Gregory T.
Published: April 2003

The Smoluchowski equation is used to derive equations for predicting the values of diffusion controlled propagation and termination rate coefficients in copolymerization. None of the resulting expressions are any more complicated than the analogous homopolymerization results. Diffusion controlled propagation rate coefficients in copolymerization are predicated to depend only very weakly on chain end type, and thus the propagation kinetics of high conversion copolymerizations are expected to be considerably simpler than those of low conversions. In considering termination, expressions for the rate coefficient for termination by ‘reaction diffusion’ are first of all derived. It is possible that under some conditions (for example, high conversions) these expressions describe the overall rate of termination, but in general, overall rates of termination will be determined by rates of center of mass diffusion, which are chain length dependent. For this reason the reaction diffusion results are incorporated into a more general treatment of termination in which chain end motion is both by translational and reaction diffusion; this treatment is envisaged as applying from intermediate conversions onward. Considerable effort is subsequently invested in developing simple descriptions of copolymerization in which rate coefficients (and in particular those for termination) are allowed to be chain length dependent. An important feature of this paper is that for every parameter usilized, a means of associating to it a value appropriate for a real system is discussed; in most cases this association is readily carried out.
Kinetic model for a polymerization process where the rate constants of both propagation and termination by monomer depend on chain‐length
Authors: Feng Jing , Yan Deyue
Published: April 2003

A kinetic model with non‐constant propagation and termination rate constants is given for a sort of anionic polymerization. The expression of molecular weight distribution and other molecular parameters are derived by a non‐steady state procedure. The effect of the reaction conditions on the molecular parameters are illustrated by numerical examples. The theoretical curves of molecular weight distribution with two or three peaks are similar to those of polymers generated in the anionic polymerization of polar monomers in nonpolar solvents.
Kinetic modelling in living polymerizations: The effect of modifiers on the degree of polymerization in batch and continuous stirred‐tank reactors
Authors: Puskas Judit E.
Published: April 2003

Equations for the calculation of the degree of polymerization in 'modified' living polymerizations (living polymerizations in the presence of deliberately added terminating and transfer agents) are developed from a mechanistic/kinetic model. It is shown that a modifier, acting by the mechanism discussed, would cause more chain transfer in a continuous stirred tank reactor (CSTR) than in a batch. This is found to be the case in the living polymerization of 1,3‐butadiene initiated by butyllithium in nonpolar solvents, such as cyclohexane, when 1,2‐butadiene was used as a modifier. Under similar conditions no chain transfer was detected in batch polymerizations, while ≈ 20% transfer was found in a CSTR. The equations developed can be used to calculate the ratio of the rates of propagation and termination, kp/kt. CSTR data yielded kp/kt ≈ 480 at 90°C; re‐evaluation of batch data published earlier by Adams et al. for the same system in hexane solvent yields kp/kt ≈ 1250 and 670 at 50° C and 70°C, respectively.
Collapse of a polymer gel induced by complex formation with linear polymers
Authors: Khokhlov Alexei R. , Kramarenko Elena Yu.
Published: April 2003

The thermodynamic theory of swelling and collapse of networks in the solution of linear polymers capable to form complexes with the network chains has been developed. The interaction of components is taken into account in the framework of the Flory‐Huggins approximation. It was shown that complex formation in most of the cases leads to the contraction of the network, which can be either continuous or discrete. The influence of the solvent quality for the network and for the complex on the behavior of the network has been studied. If the solvent is poor for complexes the network reswells at high concentration of linear chains in the outer solution. This reswelling is realized as a steep conformation transition.
Stress tensor in model polymer systems with periodic boundaries
Authors: Theodorou Doros N. , Boone Travis D. , Dodd Lawrence R. , Mansfield Kevin F.
Published: April 2003

The calculation of the stress tensor from molecular simulations of atomistic model polymer systems employing periodic boundary conditions is discussed. Starting from the dynamical equations governing the motion of sites, correct double summation forms of the atomic and the molecular virial equations are derived, which are valid for flexible, infinitely stiff and rigid chain models even in the presence of interactions between different images of the same parent macromolecule. A new expression for the true instantaneous stress (flux of momentum through the faces of the simulation box) is derived and shown to exhibit large fluctuations when applied in molecular dynamics simulations. A new equation for the thermodynamic stress, cast exclusively in terms of intermolecular forces on interaction sites, is also derived. Application to Monte Carlo simulations shows that the molecular virial expression exhibits the smallest fluctuations among all stress expressions discussed, and thus allows computation of the thermodynamic stress with least uncertainty. A scheme is developed for the calculation of surface tension from intermolecular forces only.
Statistical thermodynamics of polydisperse polymer blends with strong interaction
Authors: An Lijia , Ma Rongtang , Kou Xichun , Tang Xinyi , Jiang Bingzheng
Published: April 2003

A statistical thermodynamics theory of polydisperse polymer mixtures with strong interaction between dissimilar components based on a lattice fluid model is formulated. Expressions for the free energy, equation of state, phase stability and spinodal for a polydisperse, binary polymer mixture with strong interaction are derived.
Monte carlo study of the dynamics of star‐branched polymers
Authors: Sikorski Andrzej
Published: April 2003

A uniform star‐branched polymer model with f = 3 arms based on a simple cubic lattice was studied by means of the dynamic Monte Carlo method. The model chain is athermal with excluded‐volume interactions and it is flexible. A new type of local micromodification was introduced to make the branching point movable. Static properties of the star polymer are in accordance with other theoretical predictions and experimental evidence. Scaling of the self diffusion constant and the terminal relaxation times is close to those of the Rouse theory and to simulation results of linear chains.
Kinetics of critical fluctuations in ternary polymer solutions
Authors: Benmouna Mustapha , Fischer Erhard W. , Seils Joachim , Vilgis Thomas A.
Published: April 2003

The time evolution of the static structure factor following a sudden temperature jump ΔT is investigated in the case of a symmetric mixture of two polymers and a solvent in the optical theta conditions. The two reverse processes corresponding to ΔT > 0 and ΔT < 0 are considered, and the kinetics of approach towards the final states are investigated both in the Rouse limit and in the presence of hydrodynamic interactions.
A new application of statistical moment theory to evaluate the swelling behavior of thermo‐responsive gels
Authors: Yoshida Masaru , Asano Masaharu , Omichi Hideki , Miyajima Masaharu , Takahashi Yasuo , Yamanaka Hidetoshi , Yonezawa Noriyuki , Katakai Ryoichi
Published: April 2003

The loosely cross‐linked poly(acryloyl‐L‐proline methyl ester) gel, which is known as one of the typical thermo‐responsive gels, shows a volume transition around approximately 14°C in pure water. This volume transition is shifted to higher temperature by treatment in aqueous sodium dodecyl sulfate (SDS). The analysis of the swelling‐temperature curve (frequency distribution) was performed according to a moment analysis, in which the area under the swelling‐temperature curve (AUC), mean swelling transition temperature (MSTT) and variance of swelling transition temperature (VSTT) were calculated. It is shown that the apparent volume transition temperature can be estimated from MSTT and that VSTT can be used to characterize the shape of the corresponding curves.
Penultimate model description of the propagation kinetics for the free radical copolymerization of styrene and methyl methacrylate
Authors: Schweer Johannes
Published: April 2003

Recently experimental data on the free radical copolymerization of styrene and methyl methacrylate in bulk were shown to obey penultimate model kinetics. These data were now reevaluated with respect to copolymerization parameters by means of a simultaneous fit of the penultimate model both to the copolymer composition and to the overall propagation rate coefficient, and in dependence on the monomer feed composition. Different simultaneous fit procedures were used and compared. The following parameters are finally suggested:r11= 0,498;r21= 0,589;r22= 0,463;r12= 0,547;s1= 0,478 ands2= 0,256.
On microphase segregation of interpenetrating polymer networks
Authors: Frisch Harry L. , Grosberg Alexander Yu.
Published: April 2003

The topological entanglements between subchains of two interpenetrating polymer networks are described in the simplest approximation supposing that the primitive path of each subchain is influenced due to the shift of one network relatively to the other. The entanglement contribution to the free energy of the networks is shown to behave as 1/q2 for the state with deviation from uniform densities with the wave vector of order q. This contribution is shown to cause the microphase type of segregation.
Computer simulations of molecular motion in liquid crystals by the method of Brownian dynamics
Authors: Darinsky A. , Lyulin A. , Neelov I.
Published: April 2003

Computer simulations of the molecular motion of polymer chains in the presence of a strong nematic field were carried out by the method of Brownian dynamics. Two models were studied: the first model (linear liquid crystal) is a freely jointed chain with rigid bonds, the second model (comb‐like liquid crystal) is a chain with fixed bond angles and rigid side groups. The influence of ordering on chain conformations, orientational and translational mobility and spectra of relaxation times was investigated.
Monte Carlo studies of static properties of interacting lattice polymers with the cooperative‐motion algorithm
Authors: Gauger Andreas , Weyersberg Andrea , Pakula Tadeusz
Published: April 2003

In this paper we review some applications of the cooperative‐motion simulation algorithm to dense polymer melts. The basic idea behind the algorithm and its implementation on a computer are discussed. Furthermore we show how to include intra‐and intermolecular interactions in the simulation. Exemplary results are presented concerning on one hand the static properties of athermal and semiflexible lattice polymers and on the other hand the phase behaviour of polymer mixtures and diblock copolymers.
Perturbed enantiomorphic‐site model
Authors: Cheng H. N.
Published: April 2003

The perturbed enantiomorphic‐site (E) model was developed for the analysis of tacticity of Ziegler‐Natta polymers. Theoretical probability expressions for tacticity diads, triads, tetrads and pentads were derived, and a computer program incorporating perturbed enantiomorphic‐site and Bernoullian models was written to facilitate NMR analysis. Examples are shown of the use of the perturbed models to study the 13C NMR tacticity of poly(propylene) made with homogeneous metallocene catalysts. The perturbed E model is shown to be a suitable theoretical framework for the analysis of many polymers made with these catalysts.
Conformational characteristics of poly(vinylpyrrolidone). solvent‐dependence of the chain dimensions
Authors: Tarazona María Pilar , Saiz Enrique , Gargallo Ligia , Radic Deodato
Published: April 2003

Conformational energies as function of rotational angles over two consecutive skeletal bonds for both meso and racemic diads of poly(Nvinyl‐2‐pyrrolidone) have been computed. The results of these calculations were used to formulate a statistical model that was then employed to calculate the unperturbed dimensions of this polymer. The conformational energies are sensitive to the Coulombic interactions, which are governed by the dielectric constant, of the solvent, and to the size of the solvent molecules. Consequently, the calculated values of the polymeric chain dimensions are strongly dependent on the nature of the solvent, as it was experimentally found before.
Artificial neural system modeling of Monte Carlo simulations of polymers
Authors: Darsey Jerry A. , Soman Ashish G. , Noid Don W.
Published: April 2003

In this work, a neural network was used to learn features in potential energy surfaces and relate those features to conformational properties of a series of polymers. Specifically, we modeled Monte Carlo simulations of 20 polymers in which we calculated the characteristic ratio and the temperature coefficient of the characteristic ratio for each polymer. We first created 20 rotational potential energy surfaces using MNDO procedures and then used these energy surfaces to produce 10000 chains, each chain 100 bonds long. From these results we calculated the mean‐square end‐to‐end distance, the characteristic ratio and its corresponding temperature coefficient. A neural network was then used to model the results of these Monte Carlo calculations. We found that artificial neural network simulations were highly accurate in predicting the outcome of the Monte Carlo calculations for polymers for which it was not trained. The overall average error for prediction of the characteristic ratio was 4,82%, and the overall average error for prediction of the temperature coefficient was 0,89%.
Configurational‐conformational entropy of 1,4‐polydienes
Authors: Zhou Zhiping , Yan Deyue , Alfonso Giovanni Carlo
Published: April 2003

A method based on matrix algebra and on the rotational isomeric state scheme to study the configurational‐ conformational entropy of 1,4‐polydienes with geometrical isomerism has been developed. Bernoullian and first‐and second‐order Markovian statistics for the sequences of cis and trans units along the chains have been considered, and the explicit relation between entropy and mole fraction of cis units has been derived. Calculations performed by using available experimental data for the configurational parameters and the conformational partition functions of 1,4‐polybutadiene and 1,4‐polyisoprene show that entropy is a monotonic function of the geometrical isomer composition. While the entropy of polybutadiene increases with the content of cis units, the reverse is true for polyisoprene.
Monte Carlo simulation of kinetics and chain‐length distribution in radical polymerization
Authors: Lu Jianming , Zhang Hongdong , Yang Yuliang
Published: April 2003

In this paper, the Monte Carlo method for numerically simulating the kinetics and chain‐length distribution in radical polymerization is described. Because the Monte Carlo method is not subject to the assumption of steady‐state, it is particularly suitable for studying the kinetic behaviour before the steady‐state has been reached and for systems in which the steady‐state assumption may be violated. Illustrative applications of the algorithm given in this paper not only demonstrate convincingly both the feasibility and usefulness of the algorithm, but also provide some new insight into the illustrative examples. For the case of pseudostationary radical polymerization such as rotating‐sector and pulsed‐laser initiations, we have found that the pseudostationary radical concentration can be reached after two or three initiation periods. However, the number‐average chain‐length x̄n reaches the pseudostationary value much slower than the radical concentration. It is oscillatively reaching the pseudostationary value, and the amplitudes of the oscillations are decreasing with time. We have also found that the chain‐length distribution of the resulting polymer in the case of pseudostationary radical polymerization with termination by combination has stronger periodic modulation. Hence, it should be easier to locate the points of inflection in practice. Therefore, the rate constant of propagation, kp, can be determined precisely for systems which are dominated by a combination‐type of termination.
On bend elastic polymers
Authors: Bosch Alexandra Ten , Varichon Lionel
Published: April 2003

A review is given on the use of the bend elastic chain model for the calculation of physical properties of polymers.
NMR studies of the effects of isolated variables on polyolefin microstructure and Ziegler‐Natta catalytic sites
Authors: Cheng H. N.
Published: April 2003

Polyolefins made with heterogeneous Ziegler‐Natta catalysts contain multiple components as a result of the different catalytic sites present in the catalyst. If a series of similar catalysts are made where only one experimental variable is varied, then a family of similar polymers can be prepared where the polymer microstructure (as studied by NMR) reflects the effects of that variable. An analytical methodology is developed in this work that permits a systematic analysis to be carried out on the NMR data of such polymers. Thus, from the NMR spectra one can deduce the influence of an isolated variable on the polymer components and (indirectly) on the catalytic sites. Illustrated in this work are the effects of Lewis bases on the catalytic sites, catalyst pretreatment with a higher olefin, and catalyst grinding. The approach can be applied to study both homopolymer tacticity and copolymer sequences.