bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermoelastic and dielectric studies of poly(3,3‐dimethyl oxetane) chains
Authors: Garrido L. , Riande E. , Guzmán J. 
Published: April 2003

AbstractPoly(3,3‐dimethyl oxetane) was synthesized by ring opening polymerization of 3,3‐dimethyl oxetane. Elongation experiments were performed on unswollen elastomeric networks prepared from this polymer over the temperature range 30–90°C. The changes in the tensile stress while the networks crystallized were examined at various elongations. From thermoelastic data which were free from the effects of network crystallization, the temperature coefficient of the chain dimensions was found to be 1.1 × 10−3 K−1 in the vicinity of 60°C. The dipole moment ratio and its temperature coefficient were also measured; the average values of these parameters at 30°C were 0.206 and 2.5 × 10−3 K−1, respectively. All of these experimental‐configuration‐dependent properties were critically interpreted in terms of the rotational isomeric‐state model. In comparing theory and experiment, conclusions were obtained which confirm earlier results according to which gauche states about C—C skeletal bonds in poly(3,3‐dimethyl oxetane) are strongly favored over the alternative trans states.
Singlet energy migration and excimer formation in polymers of 2‐tert‐butyl‐6‐vinylnaphthalene
Authors: Nakahira Takayuki , Sakuma Takashi , Iwabuchi Susumu , Kojima Kuniharu 
Published: April 2003

AbstractThe homopolymer of 2‐tert‐butyl‐6‐vinylnaphthalene (BVN) and its copolymers with styrene were prepared to examine the effects of the bulky tert‐butyl groups on singlet energy migration and excimer formation among the naphthalene chromophores. The intensity of naphthalene excimer emission relative to that of monomer emission was found to depend linearly on the concentration of the potential excimer forming site, i.e., the BVN dyad fraction of the polymer. The rate of fluorescence quenching by biacetyl, on the other hand, increased only slightly with the increase in the BVN content. These results are consistent with the slow energy hopping model and suggest that the neighboring naphthalene chromophores are virtually isolated from one another owing to the unfavorable interactions of the tert‐butyl groups.
Bisphenol‐A polycarbonate–poly(butylene terephthalate) transesterification. II. Structure analysis of the reaction products by IR and 1H and 13C NMR
Authors: Devaux J. , Godard P. , Mercier J. P. , Touillaux R. , Dereppe J. M. 
Published: April 2003

AbstractThe structure of the four‐component copolyester resulting from the exchange reaction between molten bisphenol‐A polycarbonate and poly(butylene terephthalate) is analyzed as a function of the reaction time by infrared and nuclear magnetic resonance spectroscopy. By applying a statistical method developed earlier, the mean chain length of the various sequences as well as the degree of randomness is computed. The exchange reaction leads initially to the formation of a block copolyester with reduced solubility. As the reaction proceeds, a soluble random copolycondensate is progressively formed.
Epitaxial morphologies of polyoxymethylene. I. Electron microscopy
Authors: Balik C. M. , Tripathy S. K. , Hopfinger A. J. 
Published: April 2003

AbstractEpitaxial crystallization of polyoxymethylene (POM) from 0.5% iodobenzene solution has been attempted between 150 and 165°C on 11 different substrates having surface energies ranging from 136 to 1240 ergs/cm2. Included in this series are several substrates such as CaF2, SrF2, BaF2, graphite, mica, and silicon which had not been previously tested as substrates for POM epitaxy. The fluorite series materials are not good substrates for the epitaxial crystallization of POM from solution. In contrast, both rodlike and fold‐plane epitaxial morphologies have been found on the (001) surfaces of NaCl, NaF, and mica. A possible mechanism for the formation of fold‐plane epitaxy is discussed which involves solution nucleation followed by adsorption and growth of the nuclei on the substrate. It is suggested that variations observed in nucleation density of rodlike epitaxial crystals from substrate to substrate are a result of differences in degree of preferential solvent adsorption. Substrates having higher surface energies should tend to adsorb solvent more strongly and thus inhibit profuse nucleation of polymer crystals on the surface.
A two‐dimensional position‐sensitive detector for small‐angle light scattering
Authors: Tabar R. J. , Stein R. S. , Long M. B. 
Published: April 2003

AbstractA device has been developed for the rapid detection of intensity in two‐dimensional small‐angle light‐scattering patterns. The device utilizes a vidicon detector and a microprocessor. Examples of applications of the device for small‐angle light scattering from thin polymer films are presented.
Threshold tear strength of elastomers
Authors: Gent A. N. , Tobias R. H. 
Published: April 2003

AbstractTear strengths have been measured for a wide variety of molecular networks under threshold conditions; i.e., at high temperatures, low rates of tearing, and with swollen samples. For all of the polymers examined, the threshold tear strength was found to be proportional to the square root of the average molecular weight Mc of network strands, in agreement with theory. However, for the same Mc, and hence for similar values of elastic modulus, different polymers showed major differences in threshold tear strength. The tear strength of polydimethylsiloxane networks was only about one‐third that for networks of polybutadiene and cis‐polyisoprene, and the values obtained for polyphosphazene networks were only about one‐fifth as large, at the same Mc. These striking differences are attributed to differences in network strand length and extensibility for the same molecular weight. The threshold tear strengths are shown to be in satisfactory quantitative agreement with theoretically predicted values on this basis.
Chemically bound sensitizers: Dye sensitization of poly(N‐vinylcarbazole) via sulfonation and ion exchange
Authors: Pochan John M. , Gibson Harry W. 
Published: April 2003

AbstractPhotogeneration in a series of surface‐sulfonated and dye‐exchanged poly(N‐vinylcarbazole) films has been studied as a function of depth of the resultant sensitizing (photogeneration) layer. It has been shown that increasing the depth of this layer greatly affects the observed photogeneration rate, decreasing the efficiency with increasing sulfonation. Formed generator depths were from 50 to 250 Å. These results have been attributed to changes in the product μgτg, where τg is the carrier lifetime in the generation layer and μg the carrier mobility in the generation layer. Collection efficiency in the monomer dye absorption maximum and the “mer” absorption maxima are comparable.
Crack propagation in poly(2,6‐dimethyl‐1,4‐phenylene oxide), polystyrene, and their blends
Authors: Kambour R. P. , Smith S. A. 
Published: April 2003

AbstractCracks have been propagated in double‐cantilever beam specimens of poly(2,6‐dimethyl‐1,4‐phenylene oxide), polystyrene, and their blends. The plane‐strain crack propagation energy varies with crack speed, distance from crack arrest following an instability, molecular weight, and blend composition. Auxiliary measurements of moduli, yield properties, and craze initiation resistances at crack tips were carried out together with microscopic studies of the crack‐tip plastic zone. Fracture instabilities are rationalized in terms of the interplay of shear deformation with crazing in the crack‐tip plastic zone. Negative deviations from ideal behavior in the crack propagation resistance of the blends are rationalized in terms of the concurrent negative deviation in crazing resistance which in turn is thought to be related to positive deviations in shear resistance and thus to negative volumes and heats of mixing.
Low‐frequency and high‐frequency relaxations in dynamic electric birefringence of poly(γ‐benzyl‐L‐glutamate) in m‐cresol
Authors: Mori Yasushi , Ookubo Norio , Hayakawa Reinosuke , Wada Yasaku 
Published: April 2003

AbstractThe dc component Δn of the electric birefringence of poly(γ‐benzyl‐L‐glutamate) in m‐cresol is measured under an ac electric field at frequencies from 0.5 Hz to 200 kHz for solutions covering the dilute and semidilute regions. The dispersion curve indicates that at low frequencies Δn decreases with increasing frequency (low‐frequency relaxation). For high‐molecular‐weight polymers at high concentration, Δn becomes negative at high frequency and its absolute value decreases with further increase in frequency (high‐frequency relaxation). A unified theory for the two relaxations is developed on the basis of a model in which, in the semidilute regime, the rodlike polymer is confined in a cage formed by neighboring polymers and the lifetime of the cage lies between relaxation times of the two relaxations. The low‐frequency relaxation is ascribed to end‐over‐end rotation of the polymer and the high‐frequency relaxation to the rotation within a limited angle in the cage. The dependences of relaxation parameters on polymer concentration and molecular weight are reasonably explained by the theory.
Melting studies of poly(vinylidene fluoride) and its blends with poly(methyl methacrylate)
Authors: Morra Bruce S. , Stein Richard S. 
Published: April 2003

AbstractBlends of poly(vinylidene fluoride) (PVF2) and poly(methyl methacrylate) exhibit complex melting behavior when crystallized at low undercoolings. Three crystals comprised of two different PVF2 forms grow. Hoffman‐Weeks plots of the observed melting points Tm of these crystals versus crystallization temperatures are constructed. The lowest‐melting‐point species, the α form, shows a change in slope which is attributed to fewer head‐to‐head PVF2 units trapped in the crystal at higher temperatures. Defect energies in the crystal due to these units are calculated to be from 6.3 to 10.3 kJ/mol. Estimating lamellar thicknesses from the slopes of the two regions gives much more reasonable values when the high‐temperature data are used. Removal of kinetic effects that lower the observed Tm by extrapolating the data to obtain T permits the thermodynamic interaction energy density B between the two polymers to be obtained. The low‐temperature α‐form data give B = −8.83 × 106 J/m3. The high‐temperature α‐form data and the T of the γ‐form crystals both show B to vary from −5.40 × 106 to −2.96 × 107 J/m3 as the blend composition goes from 40.1 vol % to pure PVF2.
Morphological studies of poly(vinylidene fluoride) and its blends with poly(methyl methacrylate)
Authors: Morra Bruce S. , Stein Richard S. 
Published: April 2003

AbstractBoth pure poly(vinylidene fluoride) (PVF2) and its blends with poly(methyl methacrylate) (PMMA) develop a variety of morphologies when they are crystallized above the 420–424 K range. Two populations of spherulites as well as axialitelike growths are observed. Addition of the PMMA lowers the temperature where these new morphologies develop, makes the spherulites more open, causes the banding periodicity to decrease, and increases the number of small, coarse spherulites. These structures melt in three regimes. The highest‐melting‐point crystals arise only from a solid‐solid transformation of the lowest‐melting‐point ones. This solid‐state transition sometimes causes mixed spherulites to be formed in the blends. Electron and wide‐angle x‐ray diffraction show the lowest‐melting‐point species to be α crystals, while the other two are γ crystals. The highest‐melting‐point species, labeled γ′, and the α crystals seem to be more ordered than the other γ crystals.
Comparative Raman studies of molecular interactions at a dye/polymer and a dye/glass interface
Authors: Rabolt J. F. , Schlotter N. E. , Swalen J. D. , Santo R. 
Published: April 2003

AbstractIntegrated optical techniques and resonance Raman spectroscopy have been combined to investigate the intermolecular interactions at dye/polymer and dye/glass interfaces. Frequency shifts and intensity changes of bands assigned to the stretching vibrations of the bridged quinoline rings of the cyanine dye chromophore have been utilized to gain insight into the relative strength of adhesive forces at the surface. Polarized Raman measurements were made to determine the orientation of the chromophores on a poly(vinyl alcohol) surface. This was done to assess the possibility of hydrogen bond formation between the ring nitrogen atoms and the polar hydroxyl groups at the surface.
Inclusion of mobile crosslinks and lateral crystallite growth in the theory of stress‐induced crystallization
Authors: Smith K. J. 
Published: April 2003

AbstractThe theory of stress‐induced crystallization is broadened to include a reshuffling of crosslink positions as a result of changing sizes of crystalline domains and multiple crystallites of varying lateral dimensions (i.e., lateral growth). A continuous state of equilibrium throughout the amorphous component of the stretched network is postulated and, consequently, effected by requiring crosslinks to anchor about their most probable locations, which vary continuously as crystallization changes. Such features incorporated into Flory's model of stress‐induced crystallization broaden its theoretical base, placing it on a stronger, more realistic foundation.
The numerical solution of fujita's integral equation to provide estimates of molecular weight distributions
Authors: Jeffcoate J. M. , Wragg A. 
Published: April 2003

AbstractA standard model of the behavior of polymers under ultracentrifugation results in Fujita's equation for their molecular weight distribution. Fujita's and related equations are examples of Fredholm integral equations of the first kind and are thus ill posed. Two methods are described for solving the equations numerically and hence providing estimates of the molecular weight distribution. The first method involves expanding the distribution in terms of orthogonal polynomials whose coefficients are calculated from estimates of the moments of the distribution. In the second method the distribution is reconstructed by using matrix singular‐value decomposition techniques combined with an approximant expressed as a sum of B‐splines. The potential and practical limitations associated with the methods are illustrated by numerical results from a series of tests on four problems designed to represent distributions with different modal properties.
Phase transitions in mesophase macromolecules. VI. The transitions in poly(oxy‐2,2′‐dimethylazoxybenzene‐4,4′‐diyloxydodecanedioyl)
Authors: Grebowicz Janusz , Wunderlich Bernhard 
Published: April 2003

AbstractThe transitions of poly(oxy‐2,2′‐dimethylazoxybenzene‐4,4′‐diyloxydodecanedioyl) (PDAD) have been analyzed by differential scanning calorimetry, optical microscopy, and light scattering. The mesophase glass devitrifies at 288 K [ΔCp = 220 J/K mol]. Crystallization from the liquid mesophase can be described between 322 and 362 K by an Avrami expression with an exponent between 3 and 4. Results of light scattering and optical microscopy are in accord with a spherulitic morphology grown after athermal nucleation. Melting of the semicrystalline samples (crystallinity up to 58%) occurs at about 391 K. The heat of fusion of the completely crystalline sample is calculated to be only 13.55 kJ/mol. The mesophase to isotropic phase transition occurs at 418 K with a heat of transition of 4.1 kJ/mol. A general discussion of these transitions is given.
Concentrated solutions of polydisperse rodlike polymers in the isotropic and lyotropic liquid‐crystalline phases. II. Model simulation of the dielectric relaxation behavior of poly(n‐alkylisocyanates) in toluene and comparison with experimental results
Authors: Moscicki J. K. , Williams G. 
Published: April 2003

AbstractA simulation has been made of the dielectric relaxation behavior of poly(n‐hexylisocyanate) in solution covering the isotropic, biphasic, and anisotropic ranges. The simulation incorporates the Flory‐Abe statistical mechanical theory for the phase behavior of rodlike macromolecules in solution and the Warchol, Vaughan, Wang, and Pecora theory for the dynamics of a rodlike molecule in a virtual cone prescribed by the neighboring molecules. It is shown that asymmetric Gaussian, Gaussian, or Poisson distributions of molecular weight do not lead to dielectric behavior of the type observed experimentally by Moscicki, Williams, and Aharoni but addition of a high‐molecular‐weight “tail” to such distributions and taking account of the dependence of relaxation time on molecular length gives a simulation of the dielectric increment Δε, the loss maximum ε, and frequency of maximum loss fm, which vary with polymer concentration in a manner entirely consistent with the experimental data.
Interdependence of motional processes in polymers: correlation functions for nmr relaxation
Authors: Henrichs P. M. 
Published: April 2003

AbstractThe roles of both anisotropic motion and the interdependence of multiple motions in leading to nonexponential correlation functions for NMR relaxation data are explored. A motional model is developed in which rotational motions of segments of various lengths are controlled by the formation and disappearance of a suitable conformation. Such a model gives correlation functions which can be made, through adjustment of parameters, to be almost identical to correlation functions from other, quite different, models. The ability of NMR relaxation data to identify unique motional models is thus questioned.
Thermodynamics of mixtures of poly(tetramethylene oxide)s and 1, 4‐dioxane
Authors: Sharma Subhash C. , Lakhanpal Madan L. 
Published: April 2003

AbstractVapor pressures and densities of solutions of poly(tetramethylene oxide) fractions (molecular weights 650, 1000, and 2000) in 1, 4‐dioxane have been determined at 30 and 40°C. The data have been utilized to determine the activities and thermodynamic functions of dilution. Excess volumes have been determined from the density data. Flory's equation of state theory quantitatively predicts the reduced residual functions X, Xh, and Xs. Predicted as well as experimental values of Xs are found to be negative. The theory predicts correctly the sign of the excess volume but quantitative agreement between theory and experiment is not obtained.
Blends of poly(butylene terephthalate) and a polyarylate before and after transesterification
Authors: Kimura Masao , Porter Roger S. , Salee Gideon 
Published: April 2003

AbstractBlends of poly(butylene terephthalate) (PBT) and a copolyester of bisphenol‐A with 50% terephthalate‐50% isophthalate (PAr), before and after transesterification, have been studied by thermal and dynamic mechanical tests to determine crystallinity and phase behavior. Blends without transesterification, as prepared by solution precipitation, show a single Tg, indicating amorphous miscibility of PBT and PAr. A melting‐point depression for PBT crystals is not observed; this means that PBT crystallizes excluding PAr and the entropy of melting is small. The highest fractional crystallinity for PBT is obtained at 20‐35% of PAr. Transesterified blends were obtained by holding the physical blends at 250°C for up to 16 h. The transesterified systems show higher Tg's than the corresponding physical blends and also show a marked melting‐point depression and lesser PBT crystallinity at the corresponding increased PAr content.
Orientation studies on hot‐drawn tubular blown films of isotactic polypropene
Authors: Bottin Marie Francoise , Boudeulle Micheline , Guillet Jacques 
Published: April 2003

AbstractOrientation studies of hot‐drawn polypropene films were performed using small‐angle light scattering and wide‐angle and small‐angle x‐ray scattering over a wide range of deformation. At low deformation, the classical scheme of affine deformation, as several authors have pointed out, seems to be quite realistic. However, for high deformations, i.e., up to 500%, a new conception of the microfibrillar state is proposed. The microfibrils are formed of fully extended crystals which have a high degree of parallel orientation, but deviations of the units from their ideal position occur. “Wrong” chains are embedded in the lattice, long‐range order is lost, and paracrystallinity appears. A nematic arrangement develops gradually, and we suppose that the “needlelike entities” have some cylindrical symmetry with a crystalline core. The true amorphous component acts as a connection between these zones.
The diffusion of CO2, CH4, C2H4, and C3H8 in polyethylene at elevated pressures
Authors: Kulkarni S. S. , Stern S. A. 
Published: April 2003

AbstractDiffusion and solubility coefficients have been determined for the CO2−, CH4−, C2H4−, and C3H8‐polyethylene systems at temperatures of 5, 20, and 35°C and at gas pressures up to 40 atm. Diffusion coefficients were obtained from rates of gas absorption in polyethylene rods under isothermal‐isobaric conditions by means of a new diffusivity apparatus. The concentration dependence of the diffusion coefficients was represented satisfactorily by Fujita's free‐volume model, modified for semicrystalline polymers, while the solubility of all the penetrants in polyethylene was within the limit of Henry's law. Semiempirical correlations were found for the free‐volume parameters in terms of physicochemical properties of the penetrant gases and the penetrant‐polymer systems. These correlations, if confirmed, should permit the prediction of diffusion and permeability coefficients of other gases and of gas mixtures in polyethylene as functions of pressure and temperature.
Radiation‐induced crystallinity changes in linear polyethylene
Authors: Bhateja S. K. , Andrews E. H. , Young R. J. 
Published: April 2003

AbstractTwo kinds of ultrahigh‐molecular‐weight linear polyethylene (UHMW PE), together with conventional high‐density polyethylene (HDPE), were subjected to β irradiation, and changes in their properties were monitored. Elastic modulus increased steadily with dose for all materials, as did the yield stress. A dramatic rise of density with dose was observed in the UHMW PE specimens accompanied by a corresponding increase in heat of fusion, x‐ray crystallinity, and peak melting temperature. The magnitude of such changes in HDPE was much smaller. In UHMW PE specimens, the x‐ray long period simultaneously decreased but crystal thickness remained constant. No changes in long period occurred in HDPE. The effects are attributed to the scission of tie molecules in UHMW PE followed by a growth in the perfection of the crystal lamellae, and suggest a method for assessing the tie‐molecule content of such materials.
Crystallization in oriented polymers: A framework for analyzing orientation distributions
Authors: Abhiraman A. S. 
Published: April 2003

AbstractA framework is presented for analyzing the changes that occur in the orientation distribution of polymer segments when crystallization occurs in an initially amorphous precursor. Existing theories which relate crystalline orientation distribution to that of the precursor can be incorporated in this framework in a straightforward manner. The orientation distribution of segments that remain uncrystallized is inferred from a kinetic analysis of the incorporation of precursor segments into growing crystals. The relevance of such a framework in understanding polymer fabrication processes is discussed briefly with examples in fiber formation from the melt.
Ionomeric blends. II. Compatibility and dynamic mechanical properties of sulfonated cis‐1,4‐polyisoprenes and styrene/4‐ vinylpyridine copolymer blends
Authors: Zhou Zheng‐Long , Eisenberg A. 
Published: April 2003

AbstractDynamic mechanical and optical transparency methods were used to investigate the compatibility of a series of blends of sulfonated cis‐1,4‐polyisoprene and styrene/4‐vinylpyridine copolymers. It was found that compatibilization occurs at a degree of substitution less than 5%. It is suggested that proton transfer from the sulfonic acid group to vinyl pyridine, which results in the generation of specific anion‐cation interactions, is responsible for the compatibilization, since the removal of ionic interactions through esterification destroys the compatibility.