bluuebunny/crossref_metadata_2025 huggingface dataset:
Polymerization of melamine and formaldehyde in homogeneous continuous‐flow stirred‐tank reactors using functional group approach: Part B: Molecular weight distribution
Authors: Kumar Anil
Published: April 2003

Polymerization of melamine and formaldehyde in homogeneous continuous‐flow stirred‐tank reactors (HCSTRs) is reversible and leads to formation of branched polymer due to the hexafunctional nature of melamine. The reversed reaction of branched molecules depends upon the chain structure, and herein a simple model is presented to account for this. The functional group analysis of part A of this series has been extended and the molecular weight distribution (MWD) relations for HCSTRs have been solved. The MWD of the polymer is extremely sharp and the molecules are more branched compared to those for batch reactors and can be explained as follows. A given reacted bond can react with water as well as free formaldehyde through the reversed reaction, and the rate constant for the latter step is much larger. Consequently, the chain growth is limited as long as there is free formaldehyde in the reaction mass. Lower conversion of melamine and formaldehyde in HCSTRs is used to explain the behavior observed.
Process‐resolved morphology of bismaleimide matrix composites
Authors: Viot Jean‐François , Seferis James C.
Published: April 2003

A series of silicone‐modified bismaleimide resins have been examined as matrices for high performance continuous fiber‐reinforced composite materials. Detailed studies of the interrelation between processing, structure, and properties of both the neat resin and corresponding carbon‐fiber‐reinforced composite have identified that the silicone additive provides important morphological modification to the bismaleimide matrix for toughness improvements while, at the same time, retaining the elevated temperature performance. Micrographs of fracture surfaces of cured samples demonstrate remarkable similarities to fracture surfaces of rubber‐modified epoxy matrices. Specifically, a fracture surface covered with noncommunicating microcavities of 1.5 μm in diameter was observed. However, unlike rubber‐modified epoxies where the observed features are assumed to be created during fracture of the specimen, this study demonstrates that the microcavities are created during the cure process and, thus, exist in the bulk of the material before fracture. In simulated cures of the material either while obsered directly in a polarizing microscope or indirectly inside thermal analysis cells (DSC, TGA) and with examination of fractured surfaces of samples cured according to different temperature profiles, it is established that the silicone modifier, in conjunction with the processing conditions, is responsible for the morphological developments. Accordingly, a mechanism describing the observed morphology was proposed based on physical changes that the silicone additive experiences in relation to specific volatile products emitted during the cure process.
Effect of fillers on thermoplastic 1,2‐polybutadiene rubber: Mechanical and viscoelastic properties
Authors: Bhagawan S. S. , Tripathy D. K. , De S. K.
Published: April 2003

The effects of silica, carbon black, and china clay on the mechanical properties of 1,2‐polybutadiene have been investigated. They include stress–strain behavior, tensile strength, elongation, tear strength, tension set, impact strength, and hysteresis. The effect of silane coupling agent on these properties has also been studied. The stress–relaxation behavior of the filled and unfilled systems has also been compared. The rate of relaxation increases with temperature. The dynamic mechanical properties have been determined using a Rheovibron viscoelastometer at 35 Hz at different temperatures. The storage and loss moduli are enhanced by addition of fillers. Silane coupling agent increases storage modulus as well as tan δmax of the clay‐filled polymer. The suitability of Voigt and Reuss models in predicting the composite moduli is examined.
Pyrolysis‐evolved gas‐infrared spectroscopic characterization of poly(methyl methacrylate) copolymer glazing materials
Authors: Davidson R. G.
Published: April 2003

The linear temperature programmed pyrolysis of some commercial crosslinked poly(methyl methacrylate) copolymers has been examined by the technique of pyrolysis‐evolved gas‐infrared analysis. Methyl methacrylate monomer, methanol, and carbon dioxide were detected in the pyrolysis gases. The profiles of rate of evolution against temperature were used to identify the presence of occluded monomer and thermally unstable and groups such as unsaturation. The evolution profiles for methyl methacrylate and methanol were found to be characteristic for each type of crosslink. Evolution of methanol between 250°C and 300°C, and between 300°C and 350°C has been attributed to condensation reactions of carboxylic acid and primary amide groups, respectively, with adjacent ester groups. The evolution profiles were used to distinguish between samples from different manufacturers, and to identify material in aircraft canopies.
Cement mortar impregnated with poly(methyl methacrylate‐co‐styrene)
Authors: Bhattacharya Vijay K. , Maiti Mrinal M. , Maiti Sukumar
Published: April 2003

Polymer‐impregnated mortars were prepared by copolymerization of a monomer mixture of methyl methacrylate and styrene in the ratios of 13:87 and 40:60 using Co‐60 gamma radiation. The copolymerization characteristics viz. the rate of polymerization, the extent of monomer loss, polymer loading, etc., were studied. The nature and molecular weight of the extractable polymer from the composite were determined. The flexural strength of the copolymer‐impregnated composites was found to be better than that of the composites impregnated with component homopolymers.
High performance size exclusion chromatography of starch with dimethyl sulfoxide as the mobile phase
Authors: Chuang Jau‐Yi , Sydor Robert J.
Published: April 2003

Two types of high performance size exclusion chromatographic (SEC) columns were tested for the characterization of starch samples: μ Bondagel and Aquapore. The mobile phase was dimethyl sulfoxide (DMSO) containing 0.03 M sodium nitrate maintained at 80°C. The results indicated that both μ Bondagel and Aquapore can be used to determine the relative molecular weight of starch. The exclusion limits for these columns exceed ten million. Preliminary results using μ Styragel are also reported. Examples of SEC analysis of starch, including starch with anionic groups, are given.
Phase behavior for blends of styrene containing triblock copolymers with poly(2,6‐dimethyl‐1,4‐phenylene oxide)
Authors: Tucker P. S. , Barlow J. W. , Paul D. R.
Published: April 2003

The extent to which the styrene end‐blocks of three commercially available triblock copolymers can mix with a particular poly(2,6‐dimethyl‐1,4‐phenylene oxide) (Mn = 22,600 and Mw = 34,000) or PPO has been examined by investigation of the glass transition behavior of the PPO and polystyrene (PS) portions of the blends using differential scanning calorimetry. Each block copolymer has a butadiene‐based mid‐block which was hydrogenated for two of these materials, but not the third. The three copolymers differ substantially in overall molecular weight and in molecula weight of the blocks. However, in analogy with the literature on blends of homopolymer polystyrene with styrene‐based block copolymers, the molecular weight of the PS block should be the principal factor affecting the phase behavior in the present blends. Mixtures of the PPO with the block copolymers having PS blocks with M = 14,500 (nonhydrogenated midblock) and with M = 29,000 (hydrogenated mid‐block) exhibited single composition‐dependent Tgs for the hard phase, indicating complete mixing of PS segments with the PPO, for all proportions. On the other hand, the block copolymer having a PS block with M = 7,500 and a hydrogenated mid‐block exhibited two separate hard phase Tgs corresponding to an essentially pure PPO phase and a PS‐rich phase. For blends of homopolymer PS with styrene‐based block copolymers, the similar two‐phase behavior of the glassy portion can be readily explained by entropic considerations. For the present case, the favorable enthalpic contribution for mixing PPO and PS is an additional factor which seems to influence the restrictions on molecular weight for complete mixing; however, additional work is needed to develop a more quantitative assessment of this new issue.
Preparation and surface activity of water‐soluble polyesters
Authors: Chen K. M. , Liu H. J.
Published: April 2003

A novel series of water‐soluble polyester surfactants has been prepared by the polymerization of SIPM, PA, and PEG. The unique structural features of these surfactants have been confirmed by IR and NMR analyses. These water‐soluble polyester surfactants have been found to exhibit excellent surface active properties including surface tension, low‐foaming, solubilization, and dispersant properties for disperse dyes.
Permeation and separation of aqueous alcohol solutions through grafted poly(vinyl alcohol) latex membranes
Authors: Hsiue Ging‐Ho , Yang Yung‐Song , Kuo Jen‐Feng
Published: April 2003

The poly(vinyl alcohol)–acrylonitrile–2‐hydroxy ethyl methacrylate (PVA–AN–HEMA) grafted latex membrane was synthesized by grafting AN and HEMA mixture on PVA in aqueous solution. The ceric ammonium nitric in nitric acid was was used as a catalyst. This membrane has well‐balanced composition of hydrophilic and hydrophobic components and was proved by transition electron microscopy to process microstructure between continuous and disperse phases. The permeability of alcohol–water solution and separativity of phenol–water solution through this PVA–AN–HEMA membrane were studied. It was found that the permeation rate for aqueous solution as as alcohol–water was greater than that for pure water, and the separativity of phenol–water solution by pervaporation increased as the amount of PHEMA increased.
Characterization of solutions and aqueous dispersions of epoxy/amidoamine resins
Authors: Qaderi S. B. A. , Peck M. C. Paputa , Bauer D. R.
Published: April 2003

Molecular weight advancement and epoxy conversion in epoxy‐amidoamine resins have been characterized in solutions and in aqueous dispersions using viscosity, light scattering, and near‐infrared spectroscopy. By measuring the intensity of the 4532 cm−1 band in the near infrared, it is possible to determine the concentration of epoxy groups in these resins at low levels in the presence of amine and acid groups as well as solvents and other species. The epoxy‐amine reaction in these resins is found to be second order with an activation energy of around 13 kcal/mole. The addition of one mole of carboxylic acid per mole of amine functionality was sufficient to quench the epoxy‐amine reaction. Preparation of aqueous dispersions suitable for electrocoat formulation required that the extent of epoxy reaction be within a given range. Although the addition of acid completely quenched the epoxy‐amine reaction, a slow side reaction was discovered which consumes epoxy groups and ultimately changes the physical properties of coatings made from these dispersions.
Chain extenders for polyesters. VI. Properties of the polyesters chain‐extended by 2,2′‐bis(4H‐3,1‐benzoxazin‐4‐one)
Authors: Inata Hiroo , Matsumura Shunichi
Published: April 2003

Some properties of polymers derived by treating poly(ethylene terephthalate) (PET) with such hydroxyl‐addition‐type chain extenders as 2,2′‐bis(4H‐3,1‐benzoxazin‐4‐one) (BNZ) were investigated. Compared with ordinary PET, the chain‐extended PET has a slightly lower melting point and nearly equal molecular size distribution, which indicate that BNZ reacts to form linear chain‐extended polymers without branching. Oxalyl bis(anthranilate) unit copolymerized in the polyester chain showed little influence on thermal and hydrolytic stabilities. In addition, benzoxazinone groups remaining unreacted can act as a heat stabilizer to prevent the decrease in the molecular weight by the chain‐extending reaction in the solid phase. But they showed adverse effect on the hydrolytic stability by promoting hydrolysis of the polymer as much as the carboxyl groups.
The non‐Fickian diffusion of deterrents into a nitrocellulose‐based propellant
Authors: Winkler David A. , Starks Alan
Published: April 2003

The diffusion of solutions of ethyl centralite (EC), dibutylphthalate (DBP), and dinitrotoluene (DNT) into a nitrocellulose (NC) propellant is investigated. DBP and EC penetrate the propellant in a way consistent with Case II diffusion. The diffusion of DNT solutions is Fickian. The apparent activation energy for Case II diffusion is 62 kJ/mol for DBP and 66 kJ/mol for EC. Changes to coating solvent polarity have little effect on DNT and DBP penetration and merely alter the rate, not the mechanism, of EC diffusion into the propellant.
Grafting of poly(α‐chloroacrylonitrile) (α‐PCIAN) on carbon black and electrical properties of α‐PCIAN‐grafted carbon black compositions
Authors: Miyauchi Shin'Nosuke , Mino Nobuhiro , Balard Henri , Papirer Eugène , Donnet Jean Baptiste
Published: April 2003

The electrical properties of poly(α‐chloroacrylonitrile) (PCIAN) carbon black compositions were determined. These materials were prepared by polymerizing α‐chloroacrylonitrile in the presence of carbon black (GC resistors). Resistivities measurement of GC resistors shows a semiconductor‐like behavior. Moreover, the resistance change of GC resistors with electrical field strength is very large. It is concluded that the conduction of GC resistors is controlled by the thin polymer layer present at the surface of the carbon black particles. Heat degradation of such compositions was also investigated: A significant weight loss above 150°C is observed in all cases which can be attributed to thermal dehydrochlorination of PCIAN. After heat treatment at 300°C, during 1 h, the resistivities decrease of about 1 order of magnitude because of the formation of a semiconducting polyconjugated polymer by dehydrochlorination of PCIAN.
Micromechanisms of high‐energy peel failure in polyester–aluminum–polyester laminates
Authors: Brown D. J. , Lamb P. , Windle A. H.
Published: April 2003

Symmetrical polyester‐aluminum‐polyester laminates are prepared using poly(ethylene terephthalate) film subjected to a glow discharge pretreatment. Extremely high peel energies (several hundred J m−2) are achieved, and the fracture path is principally cohesive: the laminate performance thus fully exploits the bulk mechanical properties of the PET. The peel surface exhibits extensive plasticity on a scale of tens of microns, with finer ductile tearing on a scale of order 1 μm. The mechanism of peel propagation and energy dissipation is discussed with regard to the optimisation of peel strength.
Van der Waals model for filled rubbers with modified interfacial contacts
Authors: Kilian H. G. , Schenk H.
Published: April 2003

It is shown how the global deformation mechanism in filler‐loaded vulcanizates were modified by additional filler‐to‐matrix bonds. A quantitative description is given in terms of an extended van der Waals treatment including the formulation of a reduced mechanical equation of state. An interpretation of the Mullins softening is presented.
A generalized criterion for rubber toughening: The critical matrix ligament thickness
Authors: Wu Souheng
Published: April 2003

The thickness of matrix ligament is shown to be the single parameter determining whether a polymer/rubber blend will be tough or brittle. The matrix ligament is defined as the region of the matrix between two neighboring rubber particles. Specifically, the ligament thickness is the surface‐to‐surface interparticle distance. When the average ligament thickness is smaller than a critical value, a blend will be tough; when greater, it will be brittle. In other words, a sharp brittle–tough transition occurs at the critical ligament thickness. This critical parameter is independent of rubber volume fraction and particle size, and is characteristic of the matrix for a given mode, temperature and rate of deformation. What is important is the matrix ligament, not rubber particles. The single matrix parameter explains the effects of phase morphology, rubber volume fraction, particle size, particle‐size polydispersity, and particle flocculation on toughness.
The mechanical properties of rubber‐modified vinyl esters
Authors: Liao Fu‐Hua , Chu Ning‐Jo , Tong Shen‐Nan
Published: April 2003

“Vinyl esters” were prepared by reacting an epoxy resin (DGEBA) with acrylic and methacrylic acids, modified with Hycar VTBN, and cured at 90°C for 4 h with t‐butyl perbenzoate. The resultant materials showed a two‐phase structure in electron micrographs and dynamic mechanical spectra. The domain of the dispersed phase was estimated to be on the order of 10 nm in size. Infrared spectroscopy indicated extensive copolymerization of the internal double bonds or pendant vinyl groups in VTBN during the cure of the resin. The mechanical properties of the modified materials were measured, and the differences in mechanical behavior between the acrylic and methacrylic vinyl esters were discussed.
Die swell from capillary die and slit die: A theoretical study
Authors: Chiu Wen‐Yen , Shyu Goang‐Ding
Published: April 2003

Assuming polymer fluids obey the CEF equation, equations concerning die swell from capillary die and slit die were derived. The die swell of polymer increased with increasing shear rate and recoverable shear. Our theoretical predictions conformed well with the experimental data of die swell for PP and PS.
The preparation and properties of zinc coordination complexes of poly(4‐vinylpyridine‐co‐n‐butyl methacrylate) copolymers
Authors: Jacovic Mihailo S. , Perovic Ivan , MacKnight William J. , Lenz Robert W.
Published: April 2003

Two poly(4‐vinylpyridine‐co‐n‐butyl methacrylate) copolymers containing 14.2 and 30.0 mol% of 4‐vinylpyridine residues were prepared by free radical copolymerization reactions. Insoluble complexes were obtained for each copolymer by reaction with zinc chloride. The coordination complexes obtained had a molar ratio of 4‐vinylpyridine residues to zinc atoms close to 2 in both cases. The rheological behavior of each of these complexes has been compared to that of the corresponding metal‐free copolymers, which were recovered by decomplexation. The metal complexed polymers exhibited much higher glass transition temperatures and much longer high temperature relaxation times than the corresponding uncomplexed copolymers.
Reactive extrusion of polypropylene II: Degradation kinetic modeling
Authors: Suwanda D. , Lew R. , Balke S. T.
Published: April 2003

A kinetic model for the free‐radical‐initiated molecular weight degradation of polypropylene was further developed. The model has a single variable parameter, the initiator efficiency, f. Assumptions were detailed, new comparisons with experimental data presented, and model sensitivity to the value of f evaluated. The model was found to provide a good description of both molecular weight distribution and molecular weight average data from degradations carried out in a single‐screw extruder at 200 and 220°C. Data at 0.04 wt% initiator feed concentration were fit and the resulting f value used to predict results at 0.01 wt% and 0.02 wt%. In accordance with observation, the model predicted that temperature would have no effect on the molecular weight of the extrudate because the comparatively long (≥ 2.8 min) residence time in the extruder permitted degradation reactions to go to completion. The model predictions were found to depend upon the change in molecular weight distribution rather than the absolute value of the distribution data. Predictions were therefore unaffected by concentration correction in size exclusion chromatography interpretation. The model was determined to have a low sensitivity to the value of f. Hence, f was estimated to only ± 25% and it is anticipated that attempts to use the model for comparing different initiators would be limited by this characteristic. Also, because the minimum residence time in the extruder was 2.8 min, the model has yet to be tested against data at times less than this value.
Quantitative size exclusion chromatography of polypropylene II: Analysis systems
Authors: Lew R. , Cheung P. , Suwanda D. , Balke S. T.
Published: April 2003

Quantitative size exclusion chromatography (SEC) was considered a system with the following components: sample preparation, fractionation, detection, calibration, and resolution correction. Four systems were evaluated: I was 3 columns with “conventional single detector interpretation”; II was 4 columns with concentration correction and detector assessment; III was concentration correction applied to the data of I; IV was two development “mixed bed” columns. Analysis of polystyrene standards included calculation of their molecular weight averages and use of the Glöckner “T” measure of resolution as well as “specific resolution index.” Systems I and III provided the best high molecular weight results. System IV allowed 12–20 min analysis times and provided a highly linear calibration curve with very good reproducibility; however, it showed significantly worse resolution at high molecular weights. Plots of molecular weight averages determined from SEC versus their known true values were particularly useful. Concentration correction using the Rudin model moved different concentration data toward a common universal calibration curve and generally lowered molecular weight averages. Narrow polystyrene standards required relatively high concentrations for precise molecular weight averages and therefore, their averages were not good indicators of the need for concentration correction. Analysis of polypropylene samples corroborated the lower high molecular weight resolution of System III. Concentration correction did significantly change the polypropylene molecular weight distribution but did not affect the result of the kinetic model fitting.
Thermal properties of liquid crystalline aromatic random copolyesters containing two different mesogenic modifications within a polymer backbone
Authors: Yoo Young Deuk , Kim Sung Chul
Published: April 2003

Two types of semiflexible mesogenic random copolyesters which contained both nematic and smectic type repeating units within the main chain were prepared and the thermal properties as well as the mesomorphic structures were characterized by differential scanning calorimetry and by polarizing microscope. The first type of copolymer (copolymer I) contained two repeating units which differed in the rigid mesogenic groups and the second (copolymer II) contained repeating units which differed in the length of flexible segment. Copolymerization disrupted the structural regularity of the crystal, lowered the crystal–mesophase transition temperature, and destabilized the molecular order of the smectic phase. These effects were more pronounced for copolymer II. However, the isotropization temperature was changed only slightly with the incorporation of the other mesogenic component. The crystal melting temperatures of both copolymers exhibited a eutectic behavior. A smectic to nematic transition, which was not observed for the homopolymers, occurred in the range of 0.4‐0.6 mole fractions of the smectic units for copolymer I and 0.5–0.85 for copolymer II. The molecular order of the nematic phase was slightly increased as the smectic units were incorporated, while those of the smectic phase became more disordered upon addition of the nematic units.
Chemically induced graft copolymerization of acrylic acid onto polyester fabrics. I. Kinetic investigation of grafting
Authors: Okoniewski M. , Sójka‐Ledakowicz J. , Ledakowicz S.
Published: April 2003

The kinetics of grafting of acrylic acid onto poly(ethylene terephthalate) fabrics initiated by benzoyl peroxide has been studied. Extent of grafting depended upon time, concentration of the initiator and the monomer, as well as the presence of the activator used. From the temperature dependence of the initial rate of grafting the overall activation energy for grafting was found to be 90 kJ/mol. The results of the monomer and temperature dependence found in this study are consistent with the rate expression derived from a normal kinetic scheme for grafting.
Liquid diffusion into epoxy resin composites
Authors: Aminabhavi Tejraj M.
Published: April 2003

Dynamic sorption behavior of four epoxy resin matrix composites derived from fly ash, jute, mica, or vermiculite was studied in water and salt solution at 24°, 35°, and 45°C. The mass of water uptake per mass of sample was determined as a function of time. Diffusion coefficients were higher for distilled water than those for salt solution. The diffusion parameters were computed from the Arrhenius plots and the results analyzed in terms of a Fickian model. The results as obtained from weight gain assays are consistent with the view that the activation energy of diffusion is associated with the energy required to produce a space of sufficient cross‐section for the diffusing molecule to pass.
Moisture sorption of polyelectrolyte complex between poly(acrylic acid) and poly(4‐vinylpyridine)
Authors: Hirai Yoshiyuki , Nakajima Toshinari
Published: April 2003

Successive differential sorptions have been measured for the system polyelectrolyte complex of poly(acrylic acid)/poly(4‐vinylpyridine) + water vapor. The sorption data revealed that the sorption process of water vapor in the complex is controlled not only by diffusion mechanism but also by relaxation mechanism of polymer chains. It has been considered that the complex is composed of a loosely crosslinked, slightly ionized, and relatively homogeneous network structure. The sorption–desorption kinetics have also been investigated for the region of intermediate and high vapor pressures. The interval sorption–desorption curves demonstrated that the complex has the nature of the hysteresis effect in sorptions. It has been concluded that the appearance of sorption hysteresis is due to the depression of mobility of polymer chains resulting from crosslinks between carboxyl groups and pyridine rings.
Cure studies of interpenetrating networks by microdielectrometry
Authors: Holmes Brenda S. , Trask Craig A.
Published: April 2003

Microdielectrometry has been used to follow the cure kinetics of interpenetrating polymer networks (IPNs). The rate of formation of a polyurethane–poly(n‐butyl acrylate) IPN has been characterized at three temperatures. The dielectric data indicate that the relative homonetwork formation rates dominate the resultant material properties.
Postcrosslinking of linear polyesters. I melt‐blend‐type UV‐induced crosslinking agents
Authors: Inata Hiroo , Morinaga Tsutou , Matsumura Shunichi
Published: April 2003

Postcrosslinking of such linear polyesters as poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) are known to be attractive means to improve their thermal resistances without sacrificing their melt processibilities. Effective melt‐blend‐type ultraviolet‐induced crosslinking agents were investigated among allyl compounds. Such polyallyl compounds as triallyl cyanurate and triallyl isocyanurate were found to be practically promising agents from the viewpoints of crosslinkability and stability in the polyester melt. The crosslinkability of the ally compounds increased with increasing the number of the allyl groups in the molecule and electron‐withdrawing property of the neighboring group to which the allyl group was attached. The crosslinking mechanism likely includes both the polymerization of the allyl compound to form semi‐interpenetrating polymer networks in the polyester matrix and the reaction between the polyester and the allyl compound moiety. The crosslinked PET and PBT showed good mechanical properties even above the melting points of the ordinary PET and PBT.
Low‐pressure CO2 sorption in poly(vinyl benzoate) conditioned to high‐pressure CO2
Authors: Hirose Takuji , Mizoguchi Keishin , Naito Yasutoshi , Kamiya Yoshinori
Published: April 2003

Sorption of CO2 in poly(vinyl benzoate) was gravimetrically measured at pressures up to 1 atm. Sorption isotherms were determined above and below the glass transition temperature Tg from 5 to 85°C. The isotherms were analyzed by the dual‐mode sorption model assuming that the plasticizing effect of sorbed CO2 is negligible at this pressure range. The solubilities and Henry's law dissolution parameters were compared with those obtained by the high‐pressure sorption and permeation measurements. Henry's law dissolution parameters were in good agreement with one another. However, the solubilities first determined here were smaller than those determined by the high‐pressure sorption experiment at the same temperature. It was clear that the Langmuir capacity of the present specimen was smaller in spite of similar high‐pressure CO2 exposure. Relaxation of the polymer was expected to be one of the reasons. This expectation was confirmed from the observation and analysis of sorption isotherms after two kinds of treatments. After annealing above Tg, the Langmuir capacity was shown to be decreased to 1/2 or even to 1/3 from the sorption isotherms below 45°C. This means that the conditioning to the high‐pressure CO2 surely has a large effect on the nature of glassy polymer. Just after high‐pressure CO2 exposure at 25°C, increased solubility was observed. Furthermore, the slow decrease of solubility, that is, the decrease of conditioning effect, was also followed from the continual measurements at 25°C. This result reflects not only the characteristic of sorption capacity after high‐pressure CO2 exposure, but also the relaxation of polymer in glassy state.
ESCA analysis of partially converted lignocellulosic materials
Authors: Ahmed A. , Adnot A. , Kaliaguine S.
Published: April 2003

Further ESCA data of the solid residues obtained by supercritical extraction of Populus tremuloides are reported. The changes of the ESCA spectra with the severity of grinding are discussed. These data allow us to draw precise conclusions on the spatial distribution of carbonaceous recondensed material as thermal conversion proceeds. The C1s peaks are of special interest as the distribution of the four components in these peaks bears information on the nature of the chemical compounds present on the surface of the sample.
Polymerization of methyl methacrylate in micellar phase: A kinetic study
Authors: Panda Rahas B. , Patel N. , Sinha B. K.
Published: April 2003

Polymerization of methyl methacrylate (MMA) using Ce(IV) as initiator in aqueous nitric acid solution in the presence of sodium lauryl sulphate (NaLS) has been studied kinetically at a temperature range of 25–35°C. The rate of polymerization (Rp) increases with increasing concentration of NaLS, and it was also proportional to [MMA]2; but, in the presence of NaLS, the change of Rp with respect to [Ce(IV)] and [H+] were not linear and similarly the rate of Ce(IV) disappearance was not proportional to its original concentration. The overall activation energy of the polymerization process in presence of 0.01M NaLS was found to decrease by ∼ 7.0 kcal mol−1. The monomer–micelle association constant has been calculated to be 5.135 × 104 mol−1 L. The polymer obtained in surfactant medium is sparingly soluble in benzene and DMSO. From infrared spectra clear evidence of vinyl polymerization was obtained.
Memory effects in polymers. I. Orientational memory in the molten state; its relationship to polymer structure and influence on recrystallization rate and morphology
Authors: Khanna Y. P. , Reimschuessel A. C.
Published: April 2003

The influence of polymer structure on the orientational memory in the molten state has been studied by observing the crystallization behavior of the molten polymer through differential scanning calorimetry. It is shown that polymers with strong intermolecular forces (e.g., H‐bonding) retain the orientation memory even at temperatures above their equilibrium melting temperatures. The retained orientation memory of the polymer melt is shown to influence its recrystallization rate and the morphology.
Polymerization and crystallization behavior of a LaRC‐TPI powder
Authors: Hou T. H. , Bai J. M. , St. Clair T. L.
Published: April 2003

The crystallization and polymerization behavior of a crystalline LaRC‐TPI powder at elevated temperatures have been studied. The characterization methods include differential scanning calorimetry and the measurements of inherent viscosity, ηinh, and viscoelastic properties of the fully imidized samples. The as‐Received material possesses an initial crystal melting peak temperature of 272°C. For the material annealed at temperatures below 320°C, a semicrystalline polymer can be obtained. On the other hand, a purely amorphous structure is realized in the samples annealed at temperatures above 320°C. Isothermal crystallization kinetics are studied by means of the simple. Avrami equation. The likely nucleation path is attributed as an intermolecular oligomer nucleation type. The isothermal polymerization behavior is quantified by inherent viscosity measurements. A single cure is found to correlate values of Tg and ηinh for samples experiencing different thermal histories. Fully imidized amorphous and semicrystalline LaRC‐TPI samples are successfully molded based on the information obtained from thermal analyses. The viscoelastic properties of these samples are also reported.
A constitutive equation for creep in polymer concretes and their resin binders
Authors: Dharmarajan N. , Kumar S. , Armeniades C. D.
Published: April 2003

We present here a method for superposing creep measurements on polymer concrete (PC), taken at different temperatures, imposed stresses, and resin contents, onto master curves, which describe the respective responses of various PC systems and their resin binders, to compressive, tensile, and flexural loads. This treatment is extended to systems reinforced with chopped glass fiber and montmorillonite (MMT). The general applicability of this superposition is tested with creep measurements by other investigators under tensile, compressive, and flexural loads. The results make it possible to predict the long‐term creep behavior of unfilled as well as reinforced glassy polymer systems at different temperatures and load conditions from limited, short‐term data. Success of the multiple superposition suggests a generalized constitutive equation, which describes the creep compliance of these systems as a product of separable functions of each parameter in the form of shift factors for temperature (αT), stress (ασ), resin content (αυ), fiber reinforcement (αF), and MMT reinforcement (αM): J(PC) = JrαTασαυαFαMtm, where Jr is an appropriately chosen reference creep compliance. The time exponent m does not depend on the chemical nature of the polymer matrix.
Polyamide–polyurethane interpenetrating polymer networks prepared by synthesis in the melt
Authors: Decurtins S. , Hourston D. J.
Published: April 2003

Two types of interpenetrating polymer networks based on polyamide (nylon 12) and a polyurethane formed in the polyamide melt were prepared. The first type (A), which could be regarded as a semi‐2‐IPN, consisted of a polyurethane component crosslinked with trimethylolpropane whereas for the second type (B), which would meet the definition of a thermoplastic IPN, the polyurethane component was chain‐extended with butane‐1,4‐diol only. The phase morphologies of these IPNs were investigated using electron microscopy, dynamic mechanical analysis, tensile testing, and sonic velocity measurements. Electron micrographs were compared by using the conventional TEM technique and a Robinson‐type backscattered electron detector in combination with a SEM. It was concluded that the materials are phase separated, but with a fine continuous‐dispersed phase structure. For a 44 wt % polyurethane IPN a cocontinuous phase structure with a subcellular texture was indicated. One physically blended sample was compared with the analogous IPN‐type sample.
Study on the effect of dibenzylidene sorbitol as a nucleating agent on the crystallization and morphology of poly(ethylene terephthalate)
Authors: Mitra Debaprasad , Misra Ashok
Published: April 2003

The effect of dibenzylidene sorbitol (DBS) as a nucleating agent on the crystallization of poly(ethylene terephthalate) (PET) has been studied. It has been found that DBS, when incorporated into the polyester, at a 0.5–1.0 wt % level, significantly lowers the induction period and reduces the half‐time of crystallization. Thermal studies clearly show that the addition of DBS results in decreasing the temperature of crystallization, Tch, when heated from the glassy state as well as increasing the temperature of crystallization, Tcc, when cooled from the melt. Maximum spherulitic radius at 110°C has been determined for pure and nucleated PET. The spherulitic size has been found to decrease slightly with the increase in the level of DBS. Optical transmittance measurements reveal that PET containing 0.5–0.7 wt % of DBS gives the best clarity, and, beyond this level of DBS, the clarity decreases. This is probably due to the formation of agglomerates of DBS which in turn scatter visible light, thus making the film appear more hazy.
Polymer thin film integrated optics: Fabrication and characterization of polystyrene waveguides
Authors: Ives J. T. , Reichert W. M.
Published: April 2003

The fabrication and characterization of 1–3 μm polystyrene thin film integrated optical (IO) waveguides is presented. The polymer films were spun‐cast onto quartz and glass microscope slides, yielding waveguides of varying quality. The majority of defects in the polymer films appeared to be introduced during the curing process. Laser light (488 nm) was coupled into the polymer films using the prism coupling technique. The collected Raman emission was used to characterize physical and light guiding properties of acceptable polymer films. The Raman intensity spectra collected as a function of the coupling angle supplied data for the calculation of polymer film thickness and refractive index as well as providing general measure of waveguide suitability. The intensity loss due to scatter of several waveguides was also determined to rigorously evaluate waveguide quality.
Toughened mica‐filled polypropylene systems
Authors: Faulkner Douglas L.
Published: April 2003

A family of rubber‐toughened, mica‐filled polypropylene materials was developed. The rubber modifier used was an ethylene‐propylene‐diene monomer (EPDM) compound. A unique feature of this rubber‐modified system is that it can be directly molded from a dry blend. This simplifies processing by eliminating the need for melt compounding which, in turn, contributes to greater flexural moduli since attrition of the mica platelets is reduced. In addition, impact measurements were conducted as a function of temperature for EPDM/polypropylene and EPM D/poly(propylene‐ethylene) copolymer blends. The low temperature impact resistance was improved for both systems; however, the modified copolymer system maintained ductile behavior to a far lower temperature than the corresponding homopolymer system.
Molecular weight distribution control in a semibatch living‐anionic polymerization. II. Experimental study
Authors: Alassia L. M. , Couso D. A. , Meira G. R.
Published: April 2003

This work constitutes an indirect verification of a theoretical method that allows the production of polymers with prespecified molecular weight distributions (MWDs), through semibatch living‐anionic homopolymerizations. The chemical system consisted of styrene with sec‐butyllithium, in a solvent mixture of cyclohexane and tetrahydrofurane (THF). The necessary flow profiles were applied by a pair of computer‐controlled pumps, and the produced MWDs were measured by size exclusion chromatography, with correction for nonuniform instrumental spreading. The main difficulty was the estimation of the initial moles of initiator and of the concentration of impurities in the monomer solution. For such estimation, a precalibration experiment was implemented.
Water sorption, membrane potentials, and ion permeability of styrene‐grafted Bombyx mori silk fibroin membrane
Authors: Demura Makoto , Kitamura Aio , Shibamoto Akio , Asakura Tetsuo
Published: April 2003

Characterization of styrene‐grafted Bombyx mori silk fibroin membrance was investigated. It was revealed from the water sorption and 1H nuclear magnetic resonance (NMR) measurements that the amounts of water adsorbed on the silk fibroin membranes decreased by the styrene grafting and the states of water adsorbed on the styrene‐grafted silk fibroin membranes were not homogeneous; the presence of two components of water adsorbed on the membranes at 60% relative humidity was observed. In addition, the fraction of the fast component decreased with increasing styrene grafting. The membrane potentials increased with increasing of the grafting. The KCl permeability of the membrane strongly depends on the degree of styrene grafting.
Modified wheat flour–natural rubber blends. II
Authors: Hota Arun K. , Maiti Mrinal M.
Published: April 2003

Effect of cyanoethylation of starch on the properties of starch xanthide–NR vulcanizates has been studied. Significant improvements in compounding, tensile modulus, tensile strength, and retention of wet strength of the vulcanizates have been recorded. Equilibrium swelling of vulcanizates by water is also greatly suppressed. The role of cyanoethylation of starch in imparting such specific effects has been analyzed in the light of the polarity of the cyanoethyl group and its effect in lowering the critical yield stress of the modified starch for efficient dispersive mixing in NR matrix.
Viscosity and molecular weight distribution of ultrahigh molecular weight polyethylene using a high temperature low shear rate rotational viscometer
Authors: Wagner H. L. , Dillon J. G.
Published: April 2003

To obtain accurate measurements of the limiting viscosity number (LVN) or the intrinsic viscosity [η] of solutions of ultrahigh molecular weight polyethylene (UHMWPE), a low shear floating‐rotor viscometer of the Zimm‐Crothers type was constructed to measure viscosities at elevated temperatures (135°C) and near zero shear rate. The zero shear rate measurements for UHMWPE whole polymer and UHMWPE fractionated by hydrodynamic crystallization were compared with viscosity measurements at moderate and high shear rates (up to 2000s−1) carried out in a capillary viscometer. The limiting viscosity number of UHMWPE decreases, as expected, with shear rate. The higher shear rate data could not be extrapolated to yield the correct zero‐shear rate viscosities. Fractionation of UHMWPE gave 10 fractions ranging in LVN from 9 to 50 dL/g. A tentative integral molecular weight distribution for the whole polymer was calculated on the basis of the Mark‐Houwink equation, but because it had been previously established only for lower molecular weight polyethylenes, it may not be accurate. A correlation was found between the LVNs for the fractions in the two types of viscometers.
Macromolecular complexes consisting of poly(aluminum chloride), [2‐(diethylamino)ethyl]dextran hydrochloride, and potassium poly(vinyl sulfate)
Authors: Kikuchi Yasuo , Kubota Naoji
Published: April 2003

The mixture of poly(aluminum chloride) (PAC) and [2‐(diethylamino)ethyl]dextran hydrochloride (EA) were allowed to react with potassium poly(vinyl sulfate) (PVSK) to form many different water‐insoluble macromolecular complexes (MCs) in aqueous solution at various hydrogen ion concentrations. According to elemental analyses, IR spectroscopy, and solubilities of MCs, molecular structures of each MC depend on [H+]. It is suggested that the MCs obtained at pH 1.0 are products consisting of EA, PVSK, and aluminum aquo‐complex having coordination water whereas the MCs at pH 4.0 are higher molecular products consisting of EA, PVSK, and basic aluminum maltidentate complex. This result is attributable to change with [H+] in the degree of dissociation and conformation of EA, PVSK, and the dissociation of hydrated coordination of PAC. MC membranes were made by casting solutions of all kinds of MCs, and active, selective transport phenomena through a membrane of the MC prepared in a solution of pH 1.0 HCl were investigated under various conditions. Transport ratio of Na+ and the electric potential difference between the left and right sides of the membrane were measured, with a result that the higher value the membrane potential difference was long allowed to maintain, the higher the transport ratio became. According to this result, the driving force of transport is dependent on the membrane potential, Donnan potential, and diffusion potential, between both sides of the membrane. The Cl− exclusion (Donnan exclusion), however, is small due to the small cation‐exchange capacity, so that the membrane potential difference is caused to decrease rather rapidly by Cl− permeation. It was also suggested that the affinity of the carrier and both the chemical and physical properties of the MC membrane controlled the selective transport through the membrane.
Modeling of butadiene polymerization using cobalt octoate/DEAC/water catalyst
Authors: Estrada J. M. Vela , Hsu C. C. , Bacon D. W.
Published: April 2003

Two‐level fractional factorial designs were employed to study the solution polymerization of butadiene in a batch reactor using cobalt octoate/DEAC/water as catalyst. Conversion and molecular weight data obtained as functions of time were used to develop a kinetic model, and the estimated kinetic parameters were correlated empirically with four operating variables: temperature and concentrations of cobalt octoate, DEAC, and water. The experimental data indicate that at high water concentration a significant amount of oligomers is formed during early stages of polymerization, and the molecular weight of polymer increases with time. Analysis of the data suggests instantaneous initiation, first order propagation with cobalt and monomer, and transfer to monomer. Models which do not take account of the branching are shown to be incapable of fitting data for both Mn and Mw. The catalyst decay seems to follow a first‐order mechanism, but the evidence is somewhat inconclusive.
Solute diffusion in swollen membranes. IX. Scaling laws for solute diffusion in gels
Authors: Lustig Steven R. , Peppas Nikolaos A.
Published: April 2003

A scaling law was developed for the diffusion coefficient of spheroidal and ellipsoidal solutes in nonporous, equilibrium‐swollen hydrogels. The law relates the solute diffusion coefficient to the solute size, the gel mesh size, and the gel equilibrium volume degree of swelling. The law was verified by appropriate data of low and high molecular weight solute diffusion through hydrogels such as swollen networks of poly(vinyl alcohol), poly(2‐hydroxyethyl methacrylate), cellulose, and others. An additional scaling law was developed which relates the rate of release of a small or large molecule from an equilibrium swollen hydrogel with time and with morphological characteristics of the polymeric network.
Thermal and dynamic mechanical properties of hydroxypropyl cellulose films
Authors: Rials Timothy G. , Glasser Wolfgang G.
Published: April 2003

Differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) were used to characterize the morphology of solvent cast hydroxypropyl cellulose (HPC) films. DSC results were indicative of a semicrystalline material with a melt at 220°C and a glass transition at 19°C (T1), although an additional event was suggested by a baseline inflection at about 80°C (T2). Corresponding relaxations were found by DMTA. A secondary relaxation at −55°C was attributed to the interaction between hydroxyl groups of the polymer and residual diluent. The tan δ peak at T2 was found to arise from an organized phase, presumably from a liquid‐crystal mesophase formed while in solution. Crosslinking with a diisocyanate increased the peak temperature of the two primary relaxations, and resulted in a more clearly defined peak for the T2 transition. From this behavior it was concluded that both T1 and T2 are similar to glass transitions (Tg's) associated with an amorphous component and a more highly ordered phase (due to a residual liquid crystal superstructure) in the HPC bulk.