bluuebunny/crossref_metadata_2025_split huggingface dataset:
Miscibility of polyester/nitrocellulose blends: A DSC and FTIR study
Authors: Jutier Jean‐Jacques , Lemieux Even , Prud'homme Robert E. 
Published: April 2003

AbstractThe miscibility of polyester/nitrocellulose blends was investigated by differential scanning calorimetry and Fourier‐transform infrared (FTIR) spectroscopy. Two nitrocelluloses (NC) derived from wood and having different nitrogen contents (12.62 and 13.42%) were used. On the basis of the glass transition temperature criterion, poly(ϵ‐caprolactone) (PCL), poly(valerolactone), poly(ethylene adipate), and poly(butylene adipate) are miscible with nitrocellulose, whereas poly(α‐methyl α‐propyl β‐propiolactone) and poly(α‐methyl β‐proiolactone) are immiscible. The Tg versus composition curves of PCL/NC blends do not follow a monotone function but exhibit a singular point at a critical PCL volume fraction of 0.51 for NC‐1342 and 0.45 for NC‐1262 in agreement with Kovacs' theory. A shift of 17 cm‐1 of the carbonyl stretching band was observed with PCL/NC blends and is taken as evidence for hydrogen bonding interaction between the PCL carbonyl group and NC hydroxyl group. The frequency difference between the free hydroxyl absorbance and the absorbances of the hydrogen‐bonded species was found to be 85 cm‐1 in pure NC and 125 cm‐1 in PCL/NC blends; it indicates that the average strength of this interaction is stronger than the corresponding self‐associated hydrogen bonding in pure NC. The presence of a dipole‐dipole interaction between the nitrate‐ester groups of NC and the carbonyl groups of the polyesters is reported. The relative strength of the hydrogen bonding and dipole‐dipole interactions is discussed and correlated with polymer miscibility.
Energy storage in polymer chains under stress
Authors: Cook Robert 
Published: April 2003

AbstractThe local conformation and storage of energy in individual polymer chains during a deformation of a bulk polymer sample are examined by the computer simulation of a relatively simple model. It is shown that as the interaction between the chain atoms and surrounding medium increases, rotational angle motion is suppressed during the deformation, and large amounts of energy are stored in backbone bond angle and bond length distortions. The relationship of this phenomena to Tg and the implications for chain relaxation are discussed.
Isothermal crystallization of poly(vinylidene fluoride) in the presence of high static electric fields. I. Primary nucleation phenomenon
Authors: Marand H. L. , Stein R. S. , Stack G. M. 
Published: April 2003

AbstractPrimary nucleation of poly(vinylidene fluoride) (PVF2) γ‐phase crystals from the melt is affected by the presence of an electric field. Crystallization under the electric field is studied by polarized optical microscopy, thermal analysis, and wide‐angle x‐ray diffraction. Preliminary results indicate that the γ‐phase crystal nucleation rate and content are enhanced by the electric field.A modification of the classical theory of homogeneous nucleation of a crystalline phase is proposed to account for the experimental observations. Electrostatic interaction between the nucleus total polarization and the electric field contributes to the free energy of nucleation to a very large extent at low undercooling. Theoretical predictions indicate that a static electric field will increase the nucleation rate of a polar phase and will decrease the nucleation rate of a nonpolar phase. Confirmation of the former fact is observed experimentally.
Ionic miscibility enhancement in poly(tetrafluoroethylene)/poly(ethyl acrylate) blends. I. Dynamic mechanical studies
Authors: Murali R. , Eisenberg A. 
Published: April 2003

AbstractIt is shown that ion‐ion interactions resulting from a proton transfer induce considerable miscibility in blends of functionalized poly(tetrafluoroethylene) with ethyl acrylate copolymers containing 4‐vinyl pyridine. Dynamic mechanical measurements, in conjunction with transparency of the samples, are used to evaluate miscibility. It is shown that mixing conditions exert a profound effect on the properties of the final blend. The glass transition of the blend is shown to be strong function of the blend composition, as is characteristic of highly miscible systems.
Sorptive dilation of poly(vinyl benzoate) and poly(vinyl butyral) by carbon dioxide
Authors: Kamiya Yoshinori , Hirose Takuji , Mizoguchi Keishin , Terada Katsuhiko 
Published: April 2003

AbstractDilation of poly(vinyl benzoate) and poly(vinyl butyral) accompanying sorption of carbon dioxide is measured with a cathetometer under pressures up to 50 atm at 25°C. Sorption isotherms for carbon dioxide in these polymers were also determined gravimetrically. Each dilation isotherm plotted versus pressure, as well as the sorption isotherm, showed an inflection point corresponding to the glass transition of the polymer‐gas system. The dilation isotherms changed their form at that point from concave to convex to the pressure axis or to a straight line. Dilation and sorption isotherms exhibited time‐dependent hysteresis below the inflection point but not above the point. Partial molar volumes of carbon dioxide in polymers, which were determined from dilation and sorption data above the point, were found to be independent of concentration and larger than those below the point. The latter volumes depended on concentration. Based upon the extended dual‐mode sorption concept, which takes account of plasticization of polymer by sorbed gas, a dilation model was developed. Dilation data were described well by the model.
Polarized reflection spectrum and molecular orientation in uniaxially drawn poly(ethylene terephthalate)
Authors: Kaito Akira , Nakayama Kazuo , Kanetsuna Hisaaki 
Published: April 2003

AbstractThe polarized electronic spectrum of oriented poly(ethylene terephthalate) (PET) sheets was obtained from the specular reflection spectrum using the Kramers‐Kronig relationship. The surface orientation function of drawn and drawn/annealed PET sheets was determined from the dichroic ratio of the second π* ← π transition observed at 41,000 cm‐1. The bulk orientation functions in the crystalline and amorphous regions were evaluated from wide‐angle X‐ray diffraction and sonic modulus measurements. On annealing of drawn PET sheets, the crystalline orientation and crystallinity were much improved, but the amorphous orientation function showed a minor decrease. The overall molecular orientation in the surface of the drawn PET sheet was shown to be approximately equivalent to the molecular orientation in the bulk.
Plastic deformation of poly(tetramethylene oxide). II. Molecular orientation as measured by x‐ray diffraction and NMR measurements
Authors: Kretz M. , Meurer B. , Spegt P. , Weill G. 
Published: April 2003

AbstractThe orientation of the crystalline and amorphous phases in uniaxially drawn samples of polytetramethylene oxide has been studied by x‐ray and NMR methods. Pole figure measurements give the orientation of the crystalline phase. Its dependence on the draw ratio does not obey the pseudoaffine model. The crystalline fraction is derived from NMR measurements at temperatures between Tg and Tm, where the free induction decay (FID) of the unoriented sample can be analyzed in terms of a rigid (crystalline), a constrained, and an amorphous phase. Low temperature (T < Tg) measurements of the NMR second‐moment anisotropy in protonated and deuterated samples give a mean orientation of the chains higher than that corresponding to the crystalline phase. The lack of anisotropy in the tail of the FID at temperatures between Tg and Tm indicates no appreciable anisotropy in the truly amorphous interlamellar phase. From this and from the ratio of the P4/P2 orientations, factors which obey the “most probable distribution,” it is concluded that the amorphous orientation is due to the layer of constrained chains at the surface of the lamellae.
Characterization of the surface hydrolysis of kevlar‐49 fibers by diffuse reflectance FTIR spectroscopy
Authors: Chatzi E. G. , Tidrick S. L. , Koenig J. L. 
Published: April 2003

AbstractA modified diffuse reflectance technique is used to characterize the surface hydrolysis of Kevlar‐49 fibers. Treatment with 10 wt% NaOH solution produces carboxylate groups on the surface which increase rapidly up to treatment times of about 20 min at room temperature or 50 min in boiling solution. After this maximum the carboxylate groups decrease and then level out. This behavior can be explained by considering the increase as due to hydrolysis of the surface amide groups, competing with the decrease due to removal of the extensively hydrolyzed, fragmented molecules into the treatment solution. Our results shows that mild conditions (10 wt% NaOH and room temperature) as well as relatively small treatment times (less than 20 min) can be used for modifying the surface of the Kevlar‐49 fiber without destroying the skin and thus deteriorating the mechanical properties of the fiber.
On the distribution of dye molecules in stretched poly(vinyl alcohol)
Authors: van Gurp M. , van Ginkel G. , Levine Y. K. 
Published: April 2003

AbstractThe symmetry of the orientational distribution function of dye molecules in stretched PVA films is studied using polarized fluorescence. The different symmetries are monitored by a simple experimental technique in which angle‐resolved fluorescence depolarization ratios are measured. A uniaxial distribution of rhodamine 6G molecules is obtained on stretching the film at temperatures above 60°C. In contrast a biaxial distribution of trypaflavine molecules is found for stretch temperatures in the 50–115°C range. It is suggested that the hydrogen bonding between the PVA chains, and between the dye molecules and the PVA chains, influences the symmetry of the distribution upon stretching.
Edge‐excitation red shift of the fluorescence of flexible solute molecules in a poly(methyl methacrylate) polymer matrix
Authors: Al‐Hassan Khader A. 
Published: April 2003

AbstractAn excitation wavelength dependence of the fluorescence of tert‐butyl and methyl esters of 9‐anthroic acid and of tetraphenylbutadiene and tetraphenylmethylbutadiene in a poly(methyl methacrylate) (PMMA) polymer matrix is explained in terms of the presence of conformers that experience different free volumes at 77 K relative to room temperature.
A study of surface dynamics of polymers. II. Investigation by plasma surface implantation of fluorine–containing moieties
Authors: Yasuda T. , Okuno T. , Yoshida K. , Yasuda H. 
Published: April 2003

AbstractMacromolecules at the surface of a polymeric solid have considerable mobility, and the specific arrangement of functional groups of macromolecules at the surface is dictated by the environmental conditions in which the surface is placed. Consequently, the change of environmental conditions, such as immersion in water or placement in a biological surrounding, could cause a cosiderable degree of change in the surface characteristics of a polymer from those evaluated in the laboratory against ambient air. The mobile nature of a polymer surface can be investigated by surface‐implanting fluorine‐containing moieties, mainly—CF3, by the plasma implantation technique and following the disappearance and reappearance of fluorine atoms on the surface. The disappearance rates (based on the immersion time in water at room temperature) of ESCA F1s signals, the decay rates of (advancing) contact angle of water, and the recovery of these values on heat treatment of water‐immersed samples were measured as a function of crystallinity of polymer samples (at three levels of crystallinity) for poly(ethylene terephthalate) and nylon 6.
On the nature of the free volume in amorphous polymers
Authors: Brather A. 
Published: April 2003

AbstractIn a previous publication1 it was shown that the free volume in amorphous polymers cannot consist of empty sites according to the quasilattice model. In this paper it is demonstrated why theories which are based on the assumptions of this model are nevertheless partly successful. It is even possible to calculate all three jumplike alterations in the second derivatives of Gibbs free energy at the glass transition in accordance with the experimental results. As far as we know, this is the first time that, in addition to the steplike changes in the thermal expansion coefficient Δα and the specific heat Δcp, the analogous change in the compressibility Δχ can also be described correctly by a theory. The parameters for accommodation however reveal, that the quasilattice model does not apply. Consequently better‐founded equations are derived, which despite their simplicity, give excellent agreement with the experimental data. One conclusion is that if the free volume consists of cavities in the material, their mean size has to be at least ten times smaller than that of a segment of the chainlike polymer molecules.
Melt spinning of thermotropic liquid‐crystal polyesters to form ultrahigh‐modulus filaments
Authors: Itoyama Kuniyoshi 
Published: April 2003

AbstractThe properties and structure of ultrahigh‐modulus filaments were investigated for wholly aromatic copolyesters (WACPs) containing 60 and 70 mol% p‐oxybenzoate, based on p‐hydroxybenzoic acid, p,p′‐biphenol, terephthalic acid, and isophthalic acid and for poly(ethylene terephthalate co‐p‐oxybenzoate) containing 60 mol% p‐oxybenzoate. As‐spun filaments with varying degrees of molecular orientation were spun from melts by taking the spin‐extension ratio as a variable at given temperatures. The as‐spun filaments were further subjected to thermal annealing. Changes in the structural ordering with the extension ratio were monitored by wide‐angle x‐ray scattering, scanning electron microscopy, viscoelastic properties, and measurements of the thermal expansion coefficient. The increase in modulus is correlated well with the crystallite orientation at a relatively low extension ratio. However, for extension ratios above 10, the modulus of as‐spun filaments is almost independent of the crystallite orientation. Modulus values as high as 100 GPa are obtained for WACP filaments spun at extension ratios above 500. It is suggested that ultrahigh‐modulus values can be reached in highly oriented noncrystalline chains. Furthermore, the results for annealed filaments indicated that the relaxation of molecular orientation occurs partially in the oriented noncrystalline regions during the stage of long‐time annealing above Tg, leading to depression of the modulus.
Coextrusion drawing of reactor powder of ultrahigh molecular weight polyethylene
Authors: Pawlikowski Gregory T. , Mitchell Donald J. , Porter Roger S. 
Published: April 2003

AbstractCertain nascent polymers have been shown to have unusual thermal and morphological properties that are irretrievably lost once the polymer has been melted or otherwise reduced to the isotropic state. We show further that nascent ultrahigh molecular weight polyethylene “reactor powder” exhibits a remarkable ductility when uniaxially drawn by coextrusion techniques after initial compaction in film form at 100°C. When drawn at a temperature of 110°C, draw ratios of 56 have been obtained, resulting in an enhanced tensile modulus of 58 GPa. Thermal analyses and dynamic mechanical measurements were also made towards understanding the initial and final morphologies.
The observation of a sub(gel‐sol) transition in PVC/DOP gels
Authors: Gallego F. , Muñoz M. E. , Peña J. J. , Santamaría A. 
Published: April 2003

AbstractDynamic viscoelastic measurements on poly(vinyl chloride)/dioctyl phthalate gels have been carried out in parallel‐plate shear mode. Two transitions are observed: the well‐known gel‐sol transition at temperature Tf, which probably corresponds to the beginning of fusion of crystalities, and a transition, at a temperature below Tf, denoted as Ts and corresponding to phase separation. The sub(gel‐sol) Ts temperature is manifested as the transition from the first plateau zone to a second plateau in log G' versus temperature plots. Other techniques like polarizing microscopy and DSC measurements are not adequate for the detection of Ts.
Composition analysis of an ethylene–propylene block copolymer by fractionation and turbidity measurements at the lower critical solubility gap
Authors: Besombes Michel , Menguel Jean‐Francois , Delmas Genevieve 
Published: April 2003

AbstractThe composition of an ethylene‐propylene block copolymer with a nominal 15% content of ethylene by weight (EP−B15%) has been investigated through fractionation near the lower critical solution temperature (LCST). Observation of the solution heated above the boiling point of the solvent indicated that some polymer was phase separating, apparently continuously, between the LCSTs of polyethylene (PE) an polypropylene (PP) of similar molecular weight. IR and DSC analysis of three fractions obtained by twice separating the concentrated phase from the dilute phase gave the following result: EP−B15% consists of an ethylene‐rich block copolymer (93% E), an EP copolymer of intermediate composition, and a propylene‐rich copolymer (94% P). The three fractions constitute respectively 12%, 12%, and 76% of the total weights. In order to choose a suitable temperature for fractionation, a turbidity analysis of the solution of the initial polymer is made continuously during phase separation. The trace of turbidity against temperature shows three peaks of turbidity at temperatures T0, T1 and T2, which can be associated with the above fractions. A mixture of PE, PP, and a 33% E random copolymer gives a turbidity trace with characteristic temperatures very similar to that of EP‐B15% in the same solvent. Fractionation from several solvents or mixtures of solvents indicated that the composition of the fractions did not depend significantly on the nature of the solvent. Conditions for obtaining a quantitative analysis of a mixture from a thermogram are discussed. Turbidity analysis during phase separation and fractionation at the LCST can be a useful tool in analyzing and separating complex mixtures before use of powerful analytical techniques such as NMR or IR spectroscopy.
Statistics of polymer chains in orienting fields
Authors: Walasek Janusz 
Published: April 2003

AbstractThe theory of a freely jointed polymer chain is modified by introduction of interactions between dipole chain segments and an orienting field. Such a field results either from external forces (e.g. external electric or magnetic fields) or represents interactions between dipole segments of chains (molecular mean‐field). The distribution of orientations of chain segments and the free energy of a chain in such orienting fields are calculated and discussed.
Calorimetric relaxation and glass transition in poly(propylene glycols) and its monomer
Authors: Johari G. P. , Hallbrucker Andreas , Mayer Erwin 
Published: April 2003

AbstractThe glass transition temperature Tg of propylene glycol (PG) and poly(propylene glycols) (PPGs) of molecular weight up to 4000 has been measured by differential scanning calorimetry, and the activation energy and change in heat capacity ΔCp have been determined in the glass transition range. The activation energy increases with an increase in the molecular weight of the polymer, and ΔCp measured at a fixed heating rate decreases. The increase in Tg with molecular weight is remarkably more rapid for poly(propylene glycols) than for other polymers, and a limiting value of Tg is reached for a chain containing 20 monomer units. These results are discussed in terms of the Fox‐Flory and the entropy theories. The calorimetric relaxation times are comparable with the extrapolated dielectric relaxation times. The initial increase of ΔCp from PG to PPG 200 is attributed to the decrease of H‐bonding sites from 12 in 3 monomers to 4 on polymerization to PPG 200 and further decrease with increase in molecular weight to an increasingly large amplitude of the β‐process at T < Tg.
Single‐crystal‐like orientation of ultrahigh‐molecular‐weight polyethylene by uniaxial stretching
Authors: Seoul Chang , Kim Sang Yong 
Published: April 2003

AbstractDried gel film of ultrahigh‐molecular‐weight polyethylene (UHMW PE) can be drawn to 370 times its original length at 135°C. Single‐crystal mats and dried gel film of UHMW PE develop double orientation despite uniaxial stretching. This is unique for preferentially oriented UHMW PE systems. To elucidate the origin of this single‐crystal‐like orientation, precursors with different aspect ratios were prepared and drawn uniaxially. The degree of double orientation was measured by infrared spectroscopy. The origin of single‐crystal‐like orientation seems to reside in the necking region. The stacked lamellar structure is transformed into a fibrillar structure in a two‐dimensional fashion. This condition is easily provided when UHMW PE single‐crystal mat or dried gel film is drawn uniaxially. A draw ratio of 40 and aspect ratio of 40 are the optimal conditions to obtain a doubly oriented structure from UHMW PE single‐crystal mat or gel film at 135°C.
A 13C CP‐MAS NMR study of irradiated polyethylene
Authors: Pérez E. , Vanderhart D. L. 
Published: April 2003

AbstractSolid‐state 13C‐NMR was used to analyze several polyethylene samples, irradiated at room temperature with gamma rays in vacuum or with electrons in air up to a maximum dose of 200 Mrad. The main observed events were the formation of methyl ends and interior double bonds (vinylenes), as well as the disappearance of the initial vinyl ends. No signals associated with “H” or “Y” crosslinks were found in any of the samples.The partitioning of methyl ends and interior vinylenes between the crystalline and noncrystalline regions was determined only for the irradiated ultrahigh‐molecular‐weight polyethylene (UHMWPE) samples. Although concentration of methyl ends in the crystalline regions was approximately half that in the noncrystalline regions, the vinylenes had very similar concentrations in the two phases. Although some evidence for both cis and trans vinylenes appears in the spectrum of the noncrystalline regions, only one configuration (trans) seems to exist in the crystalline regions. No appreciable effect on the partitioning was detected after annealing the electron‐irradiated UHMWPE samples for 16 h at 130°C.
Kinetic analysis of curing of tetraepoxides and diamines in the presence of etherification side reactions
Authors: Tsou Andy H. , Peppas Nikolaos A. 
Published: April 2003

AbstractThe theory of branching processes is used to describe the polymer network formation resulting from the reaction of tetraepoxides with diamines using various initial compositions. Differences in reactivities of primary and secondary amine groups and the reaction between the epoxide groups and reaction‐generated hydroxyl groups are taken into account; however, intramolecular reactions in the pregel stage are neglected. Expressions are derived for the critical epoxide conversion at the gel point, molecular weight in the pregel stage, changes in sol and gel fraction in the post‐gel stage, and the concentration of elastically active network chains as a function of reaction conditions. The analysis of the simulation results shows that etherification reactions significantly raise the concentration of elastically active network chains of the mixture under stoichiometric excess of epoxide groups.