bluuebunny/crossref_metadata_2025 huggingface dataset:
Morphology and melting behaviour of poly(butylene terephthalate)
Authors: Al‐Raheil Ismail A. , Qudah Ali M. A.
Published: April 2003

A detailed description of the morphology and the complex melting behaviour of poly(butylene terephthalate) crystallized isothermally from the melt is presented. Triple, double, or single melting endotherms can deliberately be obtained by varying the heating rate in the differential scanning calorimeter (DSC). At low crystallization temperatures, Tc, triple melting endotherms were seen when the specimen was scanned at 10°C/min, while at high Tc a single endotherm was seen. In the case of the triple melting peaks, the first endotherm corresponds to melting of the imperfect crystals formed at the crystallization temperature. The second endotherm originates from melting of the perfect crystals in the initial distribution, and to some recrystallized meterial. The third endotherm is due to melting of the original crystalline material reorganized during the DSC scan. A detailed morphological study of the isothermally crystallized samples by electron microscopy showed that dominant and subsidiary lamellae in the spherulitic structure are related to perfect and imperfect crystals, respectively.
Metal chelates with some cellulose derivatives. Part III. Synthesis and structural chemistry of nickel (II) and copper (II) complexes with carboxymethyl cellulose
Authors: Hosny Wafaa M. , Hadi Afkar K. Abdel , El‐Saied Houssni , Basta Altaf H.
Published: April 2003

Cu(II) and Ni(II) complexes with three grades of carboxymethyl cellulose (CMC) with different degrees of substitution have been synthesized and characterized. Probable structures of the metal complexes are inferred from the electronic and IR spectra, elemental analysis data and magnetic moment measurements. CMC coordinates with cu(II) and Ni(II) via the carboxymethyl and hydroxyl groups. The effect of the degree of substition of the CMC on the mode of chelation is discussed. Ni(II) complexes show an octahedral geometry around the metal ion and exhibit the formula [NiL · 4H2O]Cl. Cu(II) complexes exist in the square planar form and have the formula Cu(L)2, where L is uninegatively charged bidentate CMC ligand. The ligand field parameters of Ni(II) complexes are also evaluated.
Helix formation of charged polypeptides in polyion complexes with weak and strong polyelectrolytes prepared in aqueous alcohols
Authors: Hirose Tetsuya , Satoh Mitsuru , Komiyama Jiro
Published: April 2003

Using circular dichroism, the helix contents of sodium poly(L‐glutamate) (PLGNa) and poly(L‐lysine) hydrobromide (PLLHBr) in their weak and strong polyelectrolyte complexes have been estimated in aqueous alcohol solutions. Helix (de)stabilization observed in the systems is compared with earlier results on the PLGNa/PLLHBr polyion complex.
Interfacial rheology of uniform polymer dispersions
Authors: Wang S. Q. , Inn Y. W.
Published: April 2003

The effects of high oscillatory shear on the viscosity of a model polymer dispersion of solid particles was investigated. A dispersion of glass beads in poly(dimethyl siloxane) (PDMS) is uniform and free of any agglomeration. When sheared at low stress levels, the dispersion remains uniform. At high stresses under oscillatory shear, two processes can take place. One is spatial ordering (threading) of the spherical beads that does not occur in steady shear. The other is molecular interfacial slip due to high interfacial stress in samples containing fluoro‐silane treated glass beads, leading to a lower suspension viscosity than that of samples containing bare non‐treated beads.
Polymerization of conjugated dienes initiated by soluble organosodium compounds in hydrocarbon solvents
Authors: Arest‐Yakubovich Alexander A. , Pakuro Natalia I. , Zolotareva Irina V. , Kristal'nyi Energii V. , Basova Raisa V.
Published: April 2003

Polymerization of butadiene and isoprene in hydrocarbon solvents initiated by unsolvated organosodium compounds was studied. It was found that the polymer molecular weight and the MWD are determined mainly by chain transfer to solvent and polymer, and no chain transfer to monomer was observed even in the case of isoprene. The overall polymerization rate is proportional to the concentrations of the monomer and the initiator. Apparent chain propagation rate constants were found to be 0.11 litre mol−1 s−1 for butadiene and 0.065 litre mol−1 s−1 for isoprene polymerization in heptane at 30°C. It is suggested that associated (dimeric) forms of polydienylsodium active centres play an important role in chain propagation, being responsible for a stronger chain transfer and a greater 1,2‐butadiene, or 3,4‐isoprene, unit content than in polymerization with other alkali metals.
A systematic approach to the study of multicomponent polymerization kinetics: butyl acrylate/methyl methacrylate/vinyl acetate. III. Emulsion homopolymerization and copolymerization in a pilot plant reactor
Authors: Dubé Marc A. , Penlidis Alexander
Published: April 2003

A systematic study of the terpolymerization of butyl acrylate/methyl methacrylate/vinyl acetate (BA/MMA/VAc) is being conducted. In this third stage of the study,

Parts 1 and 2: Dubé, M. A. & Penlidis, A., Polymer, 36 (1995) 587. Dubé, M. A. & Penlidis, A., Macromol. Chem. Phys., 196 (1995) 1101.

emulsion homopolymerizations and copolymerizations of the monomers comprising the BA/MMA/VAc system were performed in a 5 litre stainless steel pilot plant reactor, mainly for troubleshooting purposes and as a precursor to the detailed terpolymerization experiments to follow.

First, a search for a stable emulsion recipe was conducted. At the same time, experimental procedures were established for the 5 litre pilot plant reactor along with product characterization techniques. Finally, selective emulsion homopolymerizations and copolymerizations were run for each of the three monomers and each combination of the three monomers, respectively. The polymers produced were characterized for conversion, composition, molecular weight and particle size.

Although the emphasis of the experiments was to establish recipes, techniques, and procedures for emulsions terpolymerization, several useful observations were made regarding the kinetics even from these troubleshooting experiments.
Radical polymerization of acrylonitrile initiated by α‐picolinium p‐chlorophenacylid
Authors: Dixit Anju , Malik S. , Katiyar Sarvagya S.
Published: April 2003

The radical polymerization of acrylonitrile (AN) with α‐picolinium p‐chlorophenacylid (α‐PCPY) as initiator using carbon tetrachloride as inert solvent was investigated at 50°C. The polymerization follows ideal kinetics: the exponent values calculated for the initiator and monomer were found to be 0.5 and unity, respectively. A free radical mechanism with bimolecular termination was confirmed by the inhibiting effect of hydroquinone, a radical quencher. The rate of polymerization was a direct function of initiator (α‐PCPY) concentraction, monomer (AN) concentration and temperature. The overall activation energy calculated was 56 kJ/mol. The polymerization was favoured by polar solvents and retarded by non‐polar solvents.
Studies on permeation through polymer latex films, I. Films containing no or only low levels of additives
Authors: Steward Paul A. , Hearn John , Wilkinson Michael C.
Published: April 2003

A range of permeation techniques were employed to investigate the transport mechanisms across polymer films cast from lattices containing either no or only low levels of water soluble leachates such as residual surfactant from polymerisation or added plasticiser essential to film formation. Hydrophilic pathways can provide a mechanism of transport, in addition to partition into and solution‐diffusion in the polymer phase. Loss of porosity by low Tg polymers on drying highlights the value of solute probes in studying film morphology.
Studies on permeation through polymer latex films, II. Permeation modification by sucrose addition
Authors: Steward Paul A. , Hearn John , Wilkinson Michael C.
Published: April 2003

An investigation of the effect of leachable sucrose on the permeability of polymer latex films showed that the additive can be used to vary the solute permeability in a systematic manner, as a result of increased free volume resulting from additive leaching. However, the extent of the permeability enhancement is dependent on both the glass transition temperature of the polymer and its ability to sustain porosity and prevent pore reduction by wet sintering and/or film drying, and also the compatibility of the sucrose additive with the polymer. The loading of additive dictates how readily it is leached and, hence, the presence, or not, of continuous porosity through the full thickness of film. Although continuous porosity can be conferred on the film by the sucrose leaching, the resulting porosity still greatly inhibits the permeation of electrolyte, and the film fails well before the level of porosity approaches that required for unimpeded transport.
Electrical conduction behaviour of pure and anthracene doped poly(methyl methacrylate) foils
Authors: Keller J. M. , Vyas K. D. , Dubey R. K. , Datt S. C.
Published: April 2003

The dark conduction current in 100 μm thick pure and anthracene doped bimetallized poly(methyl methacrylate) (PMMA) foils was measured at temperatures ranging from 333 to 383 K and filds ranging from 8 to 50 kV/cm. An attempt was made to identify the nature of the current by comparing its observed dependence on electric field, temperature and dopant concentration with the respective characteristic features of the existing theories of electrical conduction. The observed characteristics suggest that the charge carriers are generated by field assisted lowering of coulombic barriers at the traps and are conducted through the bulk of the material by a hopping process between the localized states by a Jonscher–Ansari modified Poole–Frenkel mechanism. The high value of the activation energy is considered to indicate the possibility of charge carrier species inside the polymer bulk being ionic in nature.
Photochromism of novel spirooxazine. I. Investigation of the photocoloration in polymer films and fibers
Authors: Wang Ming‐Sing , Yeh Chien‐Liang , Hu Andrew Teh
Published: April 2003

The photocoloration of a novel spirooxazine, 1‐[β‐(4‐trifluoromethyl benzoyloxy)ethyl]‐3,3‐dimethyl‐spiro[indoline‐2,3′‐[3H]‐naphtho[2,1‐b]‐1,4‐oxazine] (SO), doped in different polymer films and fibers was studied. The results show that photocoloration increased with increasing concentration of spirooxazine in polymer films. The photocoloration rate of spirooxazine in PMMA is faster than that in PS due to the polarity of the polymer films. A general model for the kinetics of photocoloration of spirooxazine in polymer films is proposed. The results also show that the photocoloration rate of spirooxazine in PET is faster than that in Nylon‐6 due to the crystallinity of the polymer fibers.
Moisture cure and in‐situ silica reinforcement of epoxidized natural rubber
Authors: Hashim Azanam S. , Kohjiya S. , Ikeda Y.
Published: April 2003

Epoxidized natural rubber (ENR) was first precured with 3‐aminopropyltriethoxysilane (APS) by the normal compression molding technique. The resultant sheet was further subjected to moisture cure, via hydrolysis and condensation reactions, by soaking it in water. The moisture‐cured sample, when prepared under appropriate reaction conditions, demonstrated partial strain‐induced crystallization behavior and moderate tensile strength, as opposed to typical peroxide‐cured and sulfur‐cured vulcanizates. The suitability of the ENR–APS precured sample for in‐situ silica reinforcement by the sol–gel process, using tetraethyl orthosilicate (TEOS) as the silica precursor, was also demonstrated. Silica content as high as 36% by weight could be incorporated into the rubber, and TEOS‐to‐silica conversion of over 60% was observed. Comparative analysis with a typical peroxide‐cured sample that was subjected to the same sol–gel process indicates that the silica in the final ENR–APS sol–gel vulcanizate is chemically bound to the rubber network.
Electrically conductive TCNQ complexes of aromatic ionenes
Authors: Hochberg Gerd C.
Published: April 2003

New types of complex salts of 7,7′,8,8′‐tetracyanoquinodimethane with aromatic ionenes and their model compounds were prepared. The electrical conductivity and the activation energy were measured and discussed in relation to their structure. The effects of the nature of the aromatic unit, and the flexibility and rigidity of the polymer backbone were compared with the corresponding model compounds. The effects of frequency and temperature are discussed in terms of the molecular strucuture of the complex. The electroconductivity at room temperature of the 1 : 1 polymer complex salts was found to be between 2 × 10−4 and 7 × 10−5S/cm, while that of the model complex salts was between 1.3 × 10−3 and 6.3 × 10−3S/cm. The activation energy was found to be 0.14 eV on average. The limitation of the concept of polycationic complex salts of TCNQ for electrically conductive plastics for commerical application in the plastics industry is discussed.
Studies on kinetics of thermally initiated radical polymerization of divinyl ester monomers
Authors: Chandra R. , Soni R. K.
Published: April 2003

The divinyl ester monomers were prepared by reacting glycidyl methacrylate (GMA) with dioic acids (adipic acid, glutaric acid, succinic acid, malonic acid and oxalic acid). The reaction between the active epoxy groups of GMA and the carboxylic group of the dioic acid was catalysed by triphenyl phosphine. the curing kinetics of divinyl ester monomers were studied using benzoyl peroxide as a free radical initiator. The kinetic studies were made by differential scanning calorimetry (DSC) using the isothermal method. An explanation for the difference in the kinetic parameters with different monomers is given. A shift in the kinetic model from autocatalytic to nth order was observed in all cases. A reaction mechanism for the radical polymerization is supported by a detailed mathematical derivation and experimental results.
Multiple‐beam Fizeau fringes crossing a fibre of trilobal shaped cross‐section
Authors: Fouda I. M. , El‐Nicklawy M. M. , Hassan A. F. , Kelany A. M.
Published: April 2003

Theoretical and experimental treatments of the shape of Fizeau fringes crossing a fibre of Trilobal‐shaped cross‐section assumed to consist of a single medium are presented. A New mathematical expression is derived and used to estimate the refractive indices and the birefringence of Perlon (polycaprolactam) fibre. The resulting data are used to calculate the polarizability per unit volume. Cauchy's dispersion constants, the isotropic refractive index and the variation of refractive index with temperature are reported. The results are in agreement with previously published data. The data are illustrated by microinterferograms.
Study of in‐situ photopolymerization of chiral liquid crystal acrylate
Authors: He Liu , Zhang Shufan , Jin Shunzi , Qi Zongneng
Published: April 2003

The effect of the smectic and isotropic phase on the photo‐polymerization of the chiral liquid crystalline 4‐acryloxy‐undecanyloxy‐4′‐[S(−)‐2‐methylbutyloxy]‐biphenyl (monomer (I)) was studied using FTIR. The effect of temperature on the birefringence of surface‐oriented monomer (I) and its polymer obtained by in‐situ photopolymerization was also investigated. The results show that photopolymerization in the isotropic phase proceeds at a higher rate than in the smectic phase, when monomer conversion is less than 60%; however, when monomer conversion is above 60%, the photopolymerization rate is independent of the initial phase state of monomer (I), and a highly oriented liquid crystalline polyacrylate film can be prepared by in‐situ photopolymerization of the surface‐oriented chiral acrylate (I).
Synthesis of novel grafted materials with a view to inducing biodegradability into daily‐use polymers—I
Authors: Mohanty P. , Misra P. K. , Satpathy R. K. , Mohanty N.
Published: April 2003

Twenty polystyrene‐g‐gelatin samples were synthesised using Ce(IV) as the free radical initiator in order to make biodegradable polystyrene. Recovery of polystyrene from acid hydrolysis of the grafted sample and the appearance of new bands of gelatin at 3479 cm−1, 3235 cm−1, 1060 cm−1 and 1370 cm−1 in the IR spectrum of the grafted polystyrene sample constituted evidence of grafting, which was substantiated by evidence from 13C NMR. Thermal studies, X‐ray diffraction analysis, spectral analysis, viscosity measurements, and swelling behaviour characterised the potentially biodegradable polystyrene samples. A plausible mechanism for grafting and the probable structure of the grafted sample are suggested. Degradation studies are in progress.
Thermal and thermoelastic properties of fast extrusion furnace (FEF) carbon black loaded SBR vulcanizates
Authors: Nasr G. M. , Badawy M. M. , Gwaily S. E. , Attia G.
Published: April 2003

The effect of FEF carbon black as filler on the thermal capacity c, diffusivity a, and thermal conductivity λ, of styrene butadiene rubber (SBR) composites in the temperature range 300–420 K was studied. The filler strongly increases the thermal diffusivity, whilst strongly decreasing the thermal capacity and the thermal conductivity (except at high FEF content ≥80 phr).

The influence of the filler on the thermoelastic behaviour of the same composites was also investigated. It was found that the thermoelastic temperature change (ΔT) increased with carbon black concentration as well as the entropy change per unit extension.
Preparation, characterization and alkali metal ion permeation through nylon 666‐g‐maleic acid membranes
Authors: Usha Kulangara , Pillai Vadasseril N. Sivasankara
Published: April 2003

Nylon 666‐g‐maleic acid membranes were prepared by 60Co γ‐ray irradiation. The membranes were characterized by measuring their thickness, tensile strength, electrical resistance, membrane potential and permselectivity. Permeability coefficients of KCI, NaCl, Na2SO4, NaOH, urea and creatinine were evaluated from dialysis experiments. The charged membranes facilitated the active transport of alkali metal ions under a pH gradient.
Active centre association in anionic polymerization. Its relation to the mechanism of polymerization of dienes in non‐polar solvents
Authors: Bywater S.
Published: April 2003

The dissociation mechanism suggested for lithium‐based polymerization in many cases requires a relationships between the degree of association of the active centres and the kinetic data. This connection has recently been questioned (R. N. Young, L. J. Fetters, J. S. Huang & R. Krishnamoorti, Polymer International, 33 (1994) 217). It is the purpose of the present communication to show that this questioning is not soundly based.
Synthesis and properties of poly(tetramethylene terephthalate‐co‐ethylene terephthalate)–poly(tetramethylene ether) segmented copolymers
Authors: Shi Youheng , Wu Meiyan
Published: April 2003

A series of polyether–copolyester segmented copolymers ((PBT–PET)PTMG) based on hard segments of tetramethylene terephthalate–ethylene terephthalate copolyester (PBT–PET) and soft segments of poly(tetramethylene ether)(PTMG) was synthesized. The hard : soft segment weight ratio was 30 : 70 and the mole ratio of PBT : PET was 1 : 10; 1 : 6; 1 : 1; 3 : 1, respectively. Their mechanical properties, morphology, crystallization behavior and optical transparency were investigated and compared with poly(tetramethylene terephthalate)–poly(tetramethylene ether)(PBT–PTMG), as well as with poly(ethylene terephthalate)–poly(tetramethylene ether)(PET–PTMG), consisting of the equivalent composition ratio of hard and soft segments. It was found that the transparency could be improved by introducing a small amount of PBT into PET–PTMG through copolymerization. However, a decrease was observed in the transparency if more PBT was added. This is due to the fact that the copolymerization makes both crystallinity and crystallization rate decrease.
Cyclopolymerization of divinyl monomer with manganese (VII)—thiol redox pair
Authors: Umayavalli Manickam , Gopalakrishnan Veluchamy , Ratnasabapathy Sundramoorthy , Manickam Subramaniapillai Perumalpillai
Published: April 2003

Polymerization of non‐conjugated divinyl monomer N,N′‐methylene bisacrylamide was studied with a novel redox pair of manganese (VII)–thiol in a homogeneous gel‐free state, under varying conditions of concentration, temperature, pH and ionic strength, and the kinetic results were interpreted by a suitable mechanistic sequence from among various possibilities. Absence of gelation is attributed to the formation of a cyclic polymer. An attempt is made to correlate the structure of the reductant–oxidant complex with the observed kinetic results.
Surface morphology and annealing of poly(butylene terephthalate)
Authors: Qudah Ali M. A. , Al‐Raheil Ismail A.
Published: April 2003

A detailed description of the morphology and the complex melting behaviour of poly(butylene terephthalate) (PBT) annealed in the range 80–228°C is presented. Double melting endotherms can be obtained by annealing PBT in a differential scanning calorimeter (DSC). The lower endotherm corresponds to the melting of crystalline material formed at the annealing temperature in addition to some of the crystallized material reorganized during the quenching process. The upper melting endotherm results from the melting of a fraction of the original crystalline material reorganized during the DSC scan. Electron microscopy showed that the spherulitic structure over a wide range of annealing temperature below the melting point is unchanged. At high annealing temperatures, such as 228°C, electron micrographs showed that the narrow high melting peak is associated with the melting of isolated single crystals grown at that temperature.
Morphology and melting behaviour of poly(vinylidene fluoride) crystallized from the melt
Authors: Qudah Ali M. A. , Al‐Raheil Ismail A.
Published: April 2003

The influence of crystallization temperature on the melting behaviour and the morphology of poly(vinylidene fluoride) (PVF2) has been investigated. The DSC endotherms of PVF2 crystallized from the melt show at least two peaks. The peak areas depend on the thermal history of the samples and the heating scan rate. The area of the first peak was found to increase as the crystallization temperature or the scan rate increased. The double peak configuration was attributed to a melting–recrystallization process. Electron microscopy supports these results, for which only one type of lamella was found in the spherulitic structure.
Computer‐simulated ESR spectra of irradiated poly(olefin oxides)—effect of glass transition temperature on the ESR spectra
Authors: Murthy M. Ramakrishna , Rao B. Sanjeeva
Published: April 2003

Investigations on the effects of γ irradiation on poly(methylene oxide) (POM) and poly(ethylene oxide) (PEO) have been made employing electron spin resonance (ESR) spectroscopy. The ESR sextet and doublet spectra, recorded for POM and PEO, respectively, on irradition in air at room temperature are broadened as the temperature is lowered and show a reversible change in line shape with temperature. The spectra are analyzed by computer simulation, employing Lorentzian line‐shape functions and the least‐squares method of total curve fitting. The component spectra are evaluated and are assigned. Superposition of the component quartet, triplet, and doublet spectra, corresponding to the radicals ĊH3, ĊH2O , and OĊHO , respectively, together with a singlet due to the radicals ȮCH2 is considered to be the best fit to the observed spectrum for POM. The doublet spectrum recorded for PEO has been assigned to the radicals ĊHO . The reversible broadening of the spectra has been associated with the mechanism of molecular motions around the glass transition temperatures of these polymers.
Solid‐state 13C‐NMR studies of the aging of poly(vinylidene fluoride)/poly(methyl methacrylate) blends
Authors: Grinsted R. A. , Koenig J. L.
Published: April 2003

Solid state 13C‐NMR was used to investigate the miscibility and subsequent separation of solution‐cast blends of poly(vinylidene fluoride) (PVF2) and poly(methyl methacrylate) (PMMA) with aging for a range of compositions. It was found that one amorphous phase and intimate mixing of the polymer chains in this phase existed for all compositions of the blends, even after 2 months of aging at room temperature as determined by the proton spin lattice relaxation time T1ρH in the rotating frame, and the time constant TCH for transfer of magnetization. The T1ρH is sensitive to the spatial homogeneity of the blend via spin diffusion and would indicate the presence of phases or domains in the amorphous component of the blend larger than approximately 19 Å. The TCH is proportional to the inverse sixth power of the interatomic distances needed for transfer of magnetization from proton to carbon and would be sensitive to a separation of polymer chains in the amorphous phase with aging on the order of 4–5 Å. There was an increase of the T1ρH and TCH values with aging, indicating that a subtle separation between unlike chains in the amorphous phase was occurring although a single amorphous phase was present.
Study of a thermotropic liquid‐crystalline polyester at elevated pressures
Authors: Hsiao Benjamin S. , Shaw Montgomery T. , Samulski Edward T.
Published: April 2003

A thermotropic liquid‐crystalline copolyester of 20% hydroxybenzoic acid, 40% isophthalic acid, and 40% hydroquinone polymer was studied at elevated pressures. The characterization techniques at elevated pressures (0–1000 bar) included high‐pressure differential thermal analysis and dilatometry; at atmospheric pressure, differential scanning calorimetry, thermal optical analysis, and x‐ray analysis were employed. The mechanical properties of the solid specimens prepared at different pressures were studied by compression and dynamic rotation mechanical testing techniques. High‐pressure induced a new crystal habit in the solid state and a new mesophase in the melt. These transitions are summarized in a proposed phase diagram. Mechanical tests on the material produced at elevated pressure indicate the possibility of improved properties, implying that the pressure‐dependent morphological changes in thermotropic copolyesters could be of practical significance. The finding of a pressure‐induced mesophase also confirmed the possibility of extending the range of polymers which might exhibit liquid crystallinity via the application of pressure.
Dissociation of poly(allylammonium) cations in salt solutions
Authors: Ochiai Hiroshi , Anabuki Yasushi , Kojima Osamu , Tominaga Kazuyuki , Murakami Ichiro
Published: April 2003

Potentiometric titration in various 1‐1 salt solutions was carried out to study the dissociation behavior of the poly(allylammonium) cation (PAAH+). The titration curves show that proton release from cationic PAAH+ is markedly suppressed by addition of simple salt and depends on the counterion species. From an analysis of the titration curves it is found that the electrostatic free energy change ΔGel upon the proton release is negative in all systems examined, and its absolute value decreases with increasing ionic strength of the medium. Also, at a constant added salt concentration (0.1 mol L−1) ΔGel depends significantly on the counterion species added and increases in the order $\[ {\rm ClO}_{\rm 4}^ - > {\rm NO}_3^ - > {\rm Cl}^ - > {\rm Br}^ - > {\rm SCN}^ - > {\rm I}^ - . \]$ The value of ΔGel correlates well with the electron donor constant En of the counterions. The dissociation behavior of PAAH+ is discussed in terms of electrostatic interaction among the ionized groups on the chain, the charge shielding effect, and the ion‐solvent interaction of the added counterions.
Directional crystallization of polyethylene oxide by laser irradiation
Authors: Yang Min , Salovey R. , Allen Susan D.
Published: April 2003

Polyethylene oxide films have been directionally crystallized in a scanning beam from a tunable CO2 laser at 10.6 µm. For unidirectional scanning, elongated spherulites were produced below a scan rate of 7 µm/s, whereas parallel fibers resulted after scanning at rates below 0.2 μm/s. Higher speed processing was effected by superposing a rapid reciprocating transverse motion of the sample onto the relatively slow longitudinal scanning by the beam. In this case, spherulites were elongated below a 100 µm/s longitudinal scan rate and nucleation was completely suppressed below 25 µm/s.
Lateral growth of microparacrystals in kevlar 49 fibers irradiated by Co60
Authors: Hindeleh A. M. , Hosemann R. , Hinrichsen G. , Springer H.
Published: April 2003

Wide‐angle x‐ray diffraction experiments on Kevlar 49 fibers, irradiated with γ‐rays from a Co60 source, indicated that radiation‐induced cross‐linking in the form of H‐bonding occurred within the microparacrystals (mPC) in the lateral direction b of the unit cell and had led to an increase in the mPC size in this direction. On the other hand, the mPC size I200 along the axis and normal to the [200] netplanes did not change by radiation. In effect, the mPC size normal to the [110] netplanes increased from 4.23 nm to a maximum value of 6.04 nm at the 600 MRad dose level, after which it decreased. The mPC size in the direction of the fiber axis was 102 nm and did not change significantly by radiation (102–109 nm). Thus, essentially, the mPCs grew solely in the b direction. The paracrystalline distortion parameter (g) in the direction of the fiber axis was 2.8% and was not changed significantly by radiation (g = 2.9 ± 0.2%). The equatorial “crystallinity” maintained a value of 76% until a dose of 50 MRad and then became 73% at 100 MRad and 70% after this dose level The netplane distances were not affected by radiation.
Solid‐state cpmas 13C‐NMR studies of the reaction of an epoxy resin with masked isocyanates
Authors: Sankar S. S. , Lonikar S. V. , Gilbert R. D. , Fornes R. E. , Stejskal E. O.
Published: April 2003

It has been shown that incorporation of masked isocyanates in the MY720/DDS epoxy significantly reduces the equilibrium moisture absorption by blocking of residual functional groups ( oxirane group) by the isocyanates released in the deblocking reaction of the masked isocyanates. We have now used high resolution 13C‐CP/MAS NMR to follow the reactions in the solid state and to identify intermediates and by‐products. The deblocking reaction of the masked isocyanates also releases the corresponding alcohol, part of which may evaporate during the curing reaction. The resolution in the solid‐state spectra is good enough to identify all the reactants and the intermediates involved in the curing reaction. Difference spectra are used to emphasize changes between systems that differ in treatment or composition.
Viscoelastic behavior, order‐disorder transition, and phase equilibria in mixtures of a block copolymer and an endblock‐associating resin
Authors: Dae Han Chang , Kim Jinhwan , Man Baek Deog , Gun Chu Sung
Published: April 2003

The viscoelastic behavior, order‐disorder transition, and phase equilibria in mixtures of a block copolymer and an endblock‐associating resin were investigated. The block copolymer was a polystyrene‐block‐polyisoprene‐block‐polystyrene (KRATON® D‐1107, Shell Development Co.) copolymer. The endblock‐associating resins investigated were two different grades of a commercially available random copolymer of poly(α‐methyl styrene) and polystyrene, one with a weight‐average molecular weight \[\bar M_{\rm w}\] of 710 (KRISTALEX® 3085, Hercules Inc.) and the other with \[\bar M_{\rm w}\] = 4100 (KRISTALEX® 5140, Hercules Inc.). Mixtures of various proportions of the block copolymer and the endblock‐associating resin were prepared in toluene solvent. With the mixtures, measurements of dynamic viscoelastic properties were made, namely, dynamic storage modulus G″ and dynamic loss modulus G″ as a function of temperature from temperature scans of the samples using a Rheometrics Mechanical Spectrometer. The following observations were made. (1) The plateau modulus of the block copolymer increased with increasing amount of KRISTALEX 3085 or KRISTALEX 5140, indicating that the low‐molecular‐weight resin was associated with the polystyrene microdomains of the block copolymer. (2) When KRISTALEX 3085 (up to 30 wt %) was added to the block copolymer, the glass transition temperature (Tg) of the polyisoprene midblock of the SIS block copolymer was shifted toward higher temperatures, indicating that part of the KRISTALEX 3085 added had associated with the rubbery midblock of the block copolymer. Also investigated was the order‐disorder transition behavior of the mixtures, using a rheological technique (log G′ versus log G″ plots) recently introduced by Han and Kim. It has been found that the order‐disorder transition temperature Tr of mixtures of the SIS block copolymer and KRISTALEX 3085 decreased steadily with increasing amount of KRISTALEX 3085, whereas the addition of KRISTALEX 5140 increased the Tr of the block copolymer. It was found by light scattering and hot‐stage microscopy that macrophase separation occurred in the KRATON 1107/KRISTALEX 5140 mixtures while microdomains of polystyrene were present in the block copolymer.
Permeation, diffusion, and solution of cyclopropane in silicone rubber
Authors: Suwandi M. S. , Hirose T. , Stern S. A.
Published: April 2003

Permeability, solubility, and diffusion coefficients have been determined for cyclopropane (c‐C3H6) in silicone rubber at temperatures between −8 and 70°C at relative pressures from 0.04 to 0.30. The permeability coefficients, $&\[\bar P\]$, are of the order of 10−6 cm3 (STP) · cm/(s · cm2 · cmHg). $&\[\bar P\]$ increases slightly with increasing penetrant pressure and decreases with increasing temperature, the energy of activation for permeation being −1.27 kcal/gmol at zero pressure. The solubility of cyclopropane in silicone rubber can be represented over the experimental concentration range by the Flory‐Huggins equation. The solubility decreases with increasing temperature and the partial molar heat of solution is −4.95 kcal/gmol. The solubility coefficient in the Henry's law limit, S(0), for cyclopropane and many other gases and vapors can be correlated with (Tc/T)2, where T and Tc are the experimental and critical temperatures, respectively. The mutual diffusion coefficients, D, increase with increasing concentration and temperature, the energy of activation for diffusion being 3.68 kcal/gmol. The pressure dependence of &\[\bar P\] is described satisfactorily by a free‐volume model proposed by Fujita and extended by Stern, Frisch, and coworkers. The permeability, diffusion, and solubility behavior of cyclopropane in silicone rubber is similar to that of propane (C3H8).
Epoxy resins (DGEBA): The curing and physical aging process
Authors: Plazek D. J. , Frund Z. N.
Published: April 2003

Differential scanning calorimetry (DSC) and infrared spectroscopy (IR) were used to monitor the degree of cure of partially cured epoxy resin (Epon 828/MDA) samples. The extent of cure, as determined by residual heat of reaction, concurred with that determined by monitoring the infrared radiation absorbance of the epoxide group near 916 cm−l. The fictive temperature Tf, g was found to increase with the degree of cure, increasing rapidly during cure until reaching a value near the cure temperature Tc of 130°C (approximately 80% cure) where the material vitrified. The greatly reduced reaction rate during the final 20% of cure was not only a consequence of vitrification but, as revealed by infrared spectroscopy, the result of the depletion in the number of reactive epoxide groups. The endothermic peak areas and peak temperatures evident during the DSC scans were used as a measure of the extent of “physical aging” which took place during the cure of this resin, and after, fully cured samples were aged 37°C below their ultimate glass temperature for various periods of time. The rate of physical aging slowed as the temperature increment (Tt,g − Tc) increased. Although an endothermic peak was evident after only 1 h of cure (Tf, g = 138.3°C), such a peak did not appear until fully cured samples were aged for 16 h or more. Enthalpy data revealed that for partially cured material, the fictive temperature Tf, a, reflecting physical aging, increased with curing time. In contrast, the Tf, a, for fully cured samples decreased with sub‐Tg aging time. The characteristic jump in the heat capacity ΔCp which occurred at the Tf, g decreased as curing progressed. This decrease appears to be dependent upon the rotational and vibrational degrees of freedom of the glass. Finally, a graphical method of determining the fictive temperature Tf, a, of partially and fully cured epoxy material from measured endothermic peak areas was developed.
Diffusion competition between solvent and nonsolvent during the coagulation process of cellulose / ammonia / ammonium thiocynate fiber spinning system
Authors: Liu Cheng‐Kung , Cuculo John A. , Smith Brent
Published: April 2003

An investigation of the diffusion competition between solvent and nonsolvent in a coagulation bath is presented for the formation of a new cellulosic fiber by wet‐spinning. The system consisted of the spinnable cellulose solution with a mixture of liquid ammonia/ammonia thiocynate as the solvent and low‐molecular‐weight alcohols as the nonsolvents. The diffusion competition between solvent and nonsolvent was quantitatively characterized in terms of their mass transfer rate differences. The measurements of this rate difference were performed on the model filament shaped from gelled cellulose solutions. Results revealed that an increase in molecular size of coagulant, bath temperature, and coagulant concentration in the bath enhanced preferential diffusion of solvent from cellulose solution. Fiber spinning experiments showed that a higher value of the initial modulus of the fiber was attained with a coagulation condition providing a lower value of mass transfer rate difference. The importance of mass transfer rate difference was also shown in the influence of the fiber cross‐sectional shapes.
Rayleigh‐brillouin spectroscopy of syndiotactic poly(n‐butyl methacrylate) near the glass transition
Authors: Patterson G. D. , Jue P. K. , Stevens J. R.
Published: April 2003

We present Rayleigh‐Brillouin light scattering data of highly syndiotactic poly(n‐butyl methacrylate) [PBMA] whose glass transition temperature as measured by DSC is 55°C. The Brillouin peak shifts, Brillouin peak widths, and Landau‐Placzek ratios from −15 to 130°C are reported. The Brillouin peak widths decrease continuously through the glass transition region. This indicates a continual decrease in the strength of processes whose relaxation times are about 10−10 s with decreasing temperature even as the system becomes glassy. The Landau‐Placzek ratio above the glass transition is about 3, indicating the high optical purity of our sample. This low Landau‐Placzek ratio arises from the sample's homogeneous stereochemistry. Some of the anomalous behavior observed around 40–50°C in previous PBMA studies is explained in terms of syndiotactic regions within a largely atactic sample.
Main chain thermotropic polyesters having flexible spacers—influence of ester group linking order between mesogenic unit and flexible spacer
Authors: Jin Jung‐Il , Choi Hyang‐Suk , Choi E‐Joon , Yoon Chang‐Ju
Published: April 2003

Two series of main chain thermotropic polyesters having a decamethylene spacer were prepared and their thermal transitions and liquid crystalline properties were studied. The linking sequence of the ester bond between the mesogenic unit and spacer, i.e., versus with M and S being mesogenic unit and spacer, respectively, was found to influence profoundly the nature of the mesophase formed by the polymers. The former favors the formation of a smectic phase, while the latter favors the formation of a nematic phase. The structure of the central dicarboxylic acid moiety of the triester mesogenic units also was found to influence greatly the polymer's ability to form mesophases.
Mechanical spectrometry of alpha relaxations of high‐density polyethylene
Authors: Alberola N. , Cavaille J. Y. , Perez J.
Published: April 2003

By using an automated low‐frequency apparatus, dynamic mechanical experiments are performed on bulk‐crystallized high‐density polyethylene in the temperature range of the α relaxation. In order to characterize the key morphological features governing the presence of multiple α relaxations, we have developed a simple model from calorimetric data to assess the crystallite size distribution of samples with different thermal histories. The morphological characterizations are completed by wide‐angle x‐ray diffraction measurements. Isochronal spectrometry and frequency scans performed under isothermal conditions both exhibit two α relaxations designated α1 and α2, with increasing temperature (or increasing frequency). These two relaxations are frequency dependent but they are not thermorheologically simple processes. Some analogy is found between tan ϕ versus temperature or frequency and the biomodal lamellar size distribution curves determined from calorimetric data. Moreover, both the temperature of α2 peak and the most probable lamellar thickness of the larger lamellae depend on the thermal history of the sample: with increasing thickness of the larger lamellae, the α2 peak temperature is shifted toward higher temperature. In contrast, both the temperature of the a peak and the most probable lamellar thickness of the thinner lamellae seem to be independent of thermal history: the thinner lamellae should be formed on cooling from the remaining uncrystallized fraction. From thege findings, it is proposed that the α, and α2 relaxations have the same origins and that they could arise from defect diffusion within the thinner and thicker crystallites, respectively, with some influence of the amorphous matter in the interfacial regions.
Structure of ultrahigh‐molecular‐weight polyethylene in the solid state as studied by variable‐temperature 13C CP/MAS NMR spectroscopy
Authors: Akiyama S. , Komoto T. , Ando I. , Sato H.
Published: April 2003

In order to obtain some insight into the structure of an ultrahigh‐molecular‐weight polyethylene sample, 13C CP/MAS NMR experiments have been carried out at temperatures from 23 to −108°C. The peak for the crystalline component moves upfield with a decrease in temperature, which is contrary to what was reported previously for a melt‐crystallized polyethylene sample. On the basis of x‐ray diffraction results and quantum‐chemical calculations, it is suggested that the methylene carbons are in the distorted orthorhombic form at low temperatures.
Graft interpenetrating polymer networks of polyurethane and epoxy. I. mechanical behavior
Authors: Hsieh K. H. , Han J. L.
Published: April 2003

Polyurethanes (PU) based on poly(butylene adipate) [PU(PBA)] and poly(oxypropylene) [PU(PPG)] polyols have bean introduced into the diglycidyl ether of bisphenol A (epoxy) to form interpenetrating polymer networks (IPNs) with a PU‐grafted epoxy structure (graft‐IPNs).

The tensile strength in both PU(PPG)/epoxy and PU(PBA)/epoxy systems increases with increasing PU content. Maximum values emerge at PU/epoxy ratios between 19/81 and 27/73. This is explained as a result of the presence of the graft structure, which leads to more intimate interpenetration between the PU and epoxy in the graft‐IPNs.

Dynamic mechanical analysis (DMA) indicates that the PU introduced can be incorporated in either the α or β transition domain of the epoxy. The tensile strength of the resulting graft‐IPNs shows a significant improvement as the PU is incorporated in the α transition domain of the epoxy. It is also noted that suitable amounts of PU incorporated in both the α and β transition domains of epoxy can increase the tensile strength of the IPNs, while excessive amounts of PU introduced into both α or β transition domains tend to decrease the tensile strength of the graft‐IPNs.
Glass transition and crystal melting in semicrystalline polyimides
Authors: Cheng Stephen Z. D. , Heberer Daniel P. , Lien H.‐S. , Harris Frank W.
Published: April 2003

Quantitative thermal analysis of a family of semicrystalline polyimides containing from one to three ethylene glycol spacer units has been conducted. Special emphasis has been placed upon the changes in the thermodynamic properties resulting from the successive additions of ethylene glycol units. The solid and liquid heat capacities were measured in the temperature range 230–640 K. The solid heat capacities were also calculated from the vibration spectra of the polymers. An in‐depth description of the glass transitions, the heat capacity increases at the glass transition temperatures, and the widths of the glass transitions is provided. Three parts of the heat of fusion have been identified: Wc (H), that contributed from the high melting peak; wc (L), that contributed from the low melting peak; and wc (C), that developed during cooling after isothermal crystallization. The metastability, sequence of crystallization, and rate of reorganization of the low and high melting peaks have been investigated by stepwise crystallization and by analysis using different heating rates after isothermal crystallization. A rigid amorphous fraction is needed to explain the failure of the two‐phase (crystallinity) model.
Conductance and relaxations in the glassy and rubber states of aqueous poly( vinyl pyrrolidone): A cryofixation medium
Authors: Jain S. K. , Johari G. P.
Published: April 2003

The dielectric permittivity and loss of poly(vinyl pyrrolidone), molecular weight 40,000, containing 40% (by weight) water have been measured over the temperature range 77–325 K and frequency range 12 Hz to 0.1 MHz. A prominent relaxation due to rotational diffusion of water molecules in a hydrogen‐bonded structure occurs at T < Tg (237 K). The half‐width of the dipolar relaxation spectra is 2.27 decades and is temperature independent, which is strikingly different from the corresponding features of pure polymers. It is concluded that H‐bonded amorphous solid water persists in the glassy polymer matrix and that the H‐bonded structure contains the pyrrolidone side groups of the randomly oriented chain. The relaxation peak at T near Tg is masked by a large dc conductivity which, when expressed in terms of electric modulus, has a spectrum of half‐width 1.37 instead of 1.14 decades expected for dc conductivity alone. The contribution from dipolar reorientation in the glass‐rubber range of the PVP‐H2O solution is smaller than that in its sub‐Tg relaxation.
Experimental verification of renormalization group theoretical results for dilute macromolecular solutions. I. Light scattering data for polystyrene in solvents differing in thermodynamic quality
Authors: Woliński Leszek , Witkowski Konrad , Turzyński Zbigniew , Szafko Jerzy
Published: April 2003

Static and dynamic molecular properties are obtained from simultaneous elastic and quasielastic light scattering experiments for nine narrowly distributed polystyrene fractions in nine solvents covering the cross‐over region from theta to good‐solvent conditions. This set of consistent experimental data is compared with theoretical predictions of two renormalization group theories: the first‐order ϵ‐expansion calculations of Oono et al. and second‐order calculations within the “renormalized two‐parameter” theory of Douglas and Freed. Static properties (the penetration function) are found to be exactly described by the ϵ2‐order model, while dynamic behavior seems to be in better accord with Oono's ϵ1‐order calculations. No evidence of draining effects is detected. Solutions with benzene (and partially with toluene) exhibited atypical, nonuniversal behavior. Some features of static and dynamic exponents behavior in the crossover region are also discussed and compared with previously published theoretical predictions.