bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study of a thermotropic liquid‐crystalline polyester at elevated pressures
Authors: Hsiao Benjamin S. , Shaw Montgomery T. , Samulski Edward T. 
Published: April 2003

AbstractA 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

AbstractPotentiometric 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

AbstractPolyethylene 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

AbstractWide‐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

AbstractIt 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

AbstractThe 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

AbstractPermeability, 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

AbstractDifferential 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

AbstractAn 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

AbstractWe 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

AbstractTwo 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

AbstractBy 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

AbstractIn 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

AbstractPolyurethanes (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

AbstractQuantitative 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

AbstractThe 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

AbstractStatic 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.
Blends of styrene/acrylic acid copolymers and acrylic polymers
Authors: Brannock G. R. , Barlow J. W. , Paul D. R. 
Published: April 2003

AbstractThe miscibility of a series of styrene/acrylic acid copolymers with various polyacrylate and polymethacrylate homopolymers, as well as a series of styrene/methyl methacrylate copolymers, has been investigated. According to the binary interaction model, the miscibility diagram for styrene/acrylic acid copolymers with styrene/methyl methacrylate copolymers indicates that acid and ester groups interact endothermically. The phase behavior of the homopolymers also implies this. The analysis ignores the association and self‐association observed for the polymer blends and the low‐molecular‐weight analogs used to model them. The heat of mixing of low‐molecular‐weight analogs depended greatly on both composition and acid structure.