bluuebunny/crossref_metadata_2025_split huggingface dataset:
High density polyethylene/hydrogenated oligo(cyclopentadiene) blends: Tensile stress‐strain behavior
Authors: Cimmino S. , Di Pace E. , Martuscelli E. , Silvestre C. , Mendes L. C. , Bonfanti G. 
Published: April 2003

AbstractThe influence of hydrogenated olio(cyclopentadiene) (HOCP) on tensile mechanical properties of its blends with high density polyethylene (HDPE) has been studied at 20, 80, and 100°C. The nominal stress‐strain curves performed at 20°C indicate an increase of the modulus and a conspicuous decrease of the ultimate properties increasing the HOCP content in the blend. Blends with HOCP content > 20%‐wt are found to be very fragile at 20°C. These behaviors have been related to the presence of the HOCP‐rich phase that has the glass transition at about 55°C. At 20°C the HOCP oligomers act as a hardener for the HDPE. The nominal stress‐strain curves performed at 80 and 100°C show a strong decrease of the modulus (compared to the value at 20°C), plastic deformation for all the blends tested, and rupture of HDPE and blend samples at the beginning of the cold‐drawing. Moreover, the modulus and the ultimate parameters are found to decrease with the composition. The behaviors at 80 and 100°C have been related to several factors: the higher mobility of HDPE molecules at these temperatures compared to that at 20°C; the HOCP‐rich phase that is at temperatures higher than its glass transition, and so it acts as a plasticizer for the HDPE; and the decreases of crystallinity and number of entanglements when the HOCP is added to the HDPE component. ©1995 John Wiley & Sons, Inc.
Dielectric relaxation spectroscopy in poly(hydroxyethyl acrylates)/water hydrogels
Authors: Kyritsis A. , Pissis P. , Grammatikakis J. 
Published: April 2003

AbstractThe electrical and dielectric properties of poly(hydroxyethyl acrylate), PHEA, hydrogels were studied by means of dielectric relaxation spectroscopy in wide ranges of frequencies (5–2 × 109 Hz), temperatures (173–363 K) and water contents (0.065–0.46, g of water per gram of dry material). The secondary dipolar mechanisms (γ and βsw) and the dc conductivity mechanism were studied in detail by analyzing the dielectric susceptibility data within the complex permittivity formalism, the modulus formalism, and the complex impedance formalism. For both mechanisms molecular mobility was found to increase with increasing temperature or increasing water content (T‐f‐h superposition principle). The energy parameters and the shape parameters of the response were determined for both mechanisms at several water contents and temperatures. The temperature dependence of dc conductivity was found to change from Vogel‐Tamman‐Fulcher (VTF) type to Arrhenius type at water contents of ca. 0.30. At water contents lower than about 0.30 the hydrogels are homogeneous whereas at higher water contents a separate water phase appears. In terms of the strong/fragile classification scheme our results suggest that the PHEA hydrogels are fragile systems. ©1995 John Wiley & Sons, Inc.
Kinetic gelation predictions of species aggregation in tetrafunctional monomer polymerizations
Authors: Anseth Kristi S. , Bowman Christopher N. 
Published: April 2003

AbstractDuring the polymerization of tetrafunctional monomers, a heterogeneous distribution of species exists throughout the reaction mixture and dramatically complicates the network structural evolution. This work attempts to quantify this heterogeneity using kinetic gelation simulation predictions of a defining parameter called the heterogeneity index. The heterogeneity index directly measures how heterogeneous the polymerization is with respect to interactions of like species or pairs of species. Examples of the species are polymer segments, monomeric double bonds, pendant double bonds, initiator molecules, radicals, and free volume. By implementing this index, it is clear that the heterogeneity in the polymer network dramatically changes as a function of conversion and polymerization conditions. In particular, microgel formation and monomer pooling were characterized and quantified with the heterogeneity index. In addition to characterizing the structural heterogeneity, the influence of the heterogeneity on the initiator efficiency and trapping of free radicals was also studied and qualitatively compared to experimentally observed behavior. ©1995 John Wiley & Sons, Inc.
Ramp rate effect on polyimide film properties and morphology
Authors: Jou Jwo‐Huei , Lin Chen‐Piao , Sheu Wei‐Hwa 
Published: April 2003

AbstractThe stress in films of semirigid and rigid polyimides (PIs) on silicon (Si) substrate has been measured in situ during curing using a newly modified bending beam apparatus. By using the apparatus, the onset of residual stress in the initially solvent‐rich films has also been investigated. The stress characteristics of the PI films are strongly ramp rate dependent. Different ramp rates result in markedly different stress patterns, thermo‐mechanical properties, and film morphologies. The residual stress at room temperature after curing is scattered around 23–31 MPa for the films of pyromellitic dianhydride‐4,4′‐oxydianiline (PMDA‐ODA). For pyromellitic dianhydride‐p‐phenylenediamine (PMDA‐PDA), it systematically increases from −6 to 28 MPa for ramp rate increasing from 0.5 to 10°C/min. The residual stress is very low in the slowly cured PMDA‐PDA films. However, these films have gone through a very high‐stress transient state during curing. The maximum transient stress is comparatively higher in the films of PMDA‐PDA than in PMDA‐ODA. Slowly cured PMDA‐PDA films exhibit high structural ordering, high in‐plane anisotropy, and low coefficient of thermal expansion. ©1995 John Wiley & Sons, Inc.
Self‐diffusion in melts of statistical copolymers: The effect of changes in microstructural composition
Authors: Losch Andreas , Salomonovic Radan , Steiner Ullrich , Fetters Lewis J. , Klein Jacob 
Published: April 2003

AbstractWe have used nuclear reaction analysis to measure diffusion coefficients D in couples consisting of hydrogenated polybutadienes of structure (C2H3(C2H5))x(C4H8)1−x and their partly deuterated counterparts. The 1,2‐ and 1,4‐olefinic isomers are randomly distributed along the chains and the mean vinyl fraction x varies between 0.38 and 0.94. We find that the effective monomeric mobility D0 [defined by D = D0(Ne/N2) for each copolymer, where N is the backbone length and Ne the entanglement spacing] decreases monotonically with increasing vinyl content x. Over the range of microstructures and temperatures T (−14−40°C) investigated we find log(D0/T) varies smoothly with (T − Tg), where Tg is the glass transition temperature of the respective melts. An analysis of our data in terms of a simple activated rate process model suggests that D0 is controlled by thermally activated hopping of segments whose effective volume is close to that of the respective statistical segment lengths of the copolymeric chains. ©1995 John Wiley & Sons, Inc.
Interfacial tension between low molecular weight polymers from the static analysis of cylindrical drops and their break‐up dynamics
Authors: Quirion François , Pageau Johanne 
Published: April 2003

AbstractA spinning drop tensiometer was used to measure the interfacial tension between the coexisting phases of mixtures of low molecular weight polypropylene glycol, Mw = 1000, and polyethylene glycol, Mw = 300, 400, or 550. Two types of experiments gave concordant interfacial tensions. First, the static analysis of the equilibrium diameter of cylindrical drops according to Vonnegut and, second, Tomotika's dynamic analysis of Rayleigh instabilities caused by a sharp decrease of the angular speed. The end‐pinching process also lead to the break‐up of the drops and it was characterized by a rapid expansion of the hemispherical ends followed by a slower pinching step. The pinching rate increases as the final angular speed decreases while the growth rate of Rayleigh instabilities shows no definite trends in the range 118‐245 rad · s−1. It is shown that the end‐pinching of long cylindrical drops can be analyzed in terms of short fiber retraction to get the interfacial tension. © 1995 John Wiley & Sons, Inc.
Evaluation of the orientation coefficient for the c axis in poly(ethylene terephthalate) fibers
Authors: Auriemma Finizia , Guerra Gaetano , Parravicini Lidia , Petraccone Vittorio , Russo Giuseppe 
Published: April 2003

AbstractThe literature methods for the determination of the mean of the crystallite orientation distribution for the c axis, that is of the orientation coefficient fc, for poly(ethylene terephthalate) (PET), based on the azimuthal scan of the (105) reflection, are reviewed. These methods appear unsuitable for samples presenting the “tilted orientation”; that is, the molecular chain axis inclined by some degrees with respect to the fiber axis, as frequently occurs for PET fibers. A new method for the determination of fc for PET, also based on the azimuthal scan of the (105) reflection (which can be applied also to samples with “tilted orientation”), is proposed. This method implies as a first step the determination of the tilt angle, for which the complete fiber pattern is required. A possible simplifying assumption, which allows use of the sole azimuthal (105) profile and makes the method also applicable to poorly oriented samples (for which the determination of the tilt angle is not easy), is also discussed. © 1995 John Wiley & Sons, Inc.
The effects of annealing on fatigue crack propagation in polyethylene
Authors: Strebel J. J. , Moet A. 
Published: April 2003

AbstractFatigue crack propagation tests on annealed and quenched medium‐density polyethylene showed the annealed specimens to have much lower resistance to crack initiation and subsequent propagation. Although the same fracture mechanism, in which the brittle crack gradually becomes more ductile, prevailed in both cases, the voided and fibrillated crack tip root craze in the annealed material was much weaker that the nonfibrillated quenched root craze. Microstructural analyses indicate that the annealed material had separate crystallite populations, whereas the quenched material had a more homogeneous morphology. The highest melting fraction of the annealed material was composed of lamellae that were about 270 Å thick, and the quenched lamellae were estimated to be 160 Å thick. The reduced fatigue crack propagation resistance of the annealed material was suggested to be a result of a lower concentration of tie molecules and its reduced damping capability, compared to the quenched material. © 1995 John Wiley & Sons, Inc.
Structure and molecular conformation of tussah silk fibroin films: Effect of methanol
Authors: Tsukada Masuhiro , Freddi Giuliano , Monti Patrizia , Bertoluzza Alessandro , Kasai Nobutami 
Published: April 2003

AbstractStructural changes of tussah (Antheraea pernyi) silk fibroin films treated with different water‐methanol solutions at 20°C were studied as a function of methanol concentration and immersion time. X‐ray diffraction measurements showed that the α‐helix structure, typical of untreated tussah films, did not change for short immersion times (2 min), regardless of methanol concentration. However, crystallization to β‐sheet structure was observed following immersion of tussah films for 30 min in methanol solutions ranging from 20 to 60% (v/v). IR spectra of tussah films untreated and methanol treated for 2 min exhibited strong absorption bands at 1265, 892, and 622 cm−1, typical of the α‐helix conformation. The intensity of the bands assigned to the β‐sheet conformation (1245, 965, and 698 cm−1) increased for the sample treated with 40% methanol for 30 min. Raman spectra of tussah films with α‐helix molecular conformation exhibited strong bands at 1657 (amide I), 1263 (amide III), 1106, 908, 530, and 376 cm−1. Following α → β conformational transition, amide I and III bands shifted to 1668, and to 1241, 1230 cm−1, respectively. The band at 1106 cm−1 disappeared and new bands appeared at 1095 and 1073 cm−1, whereas the intensity of the bands at 530 and 376 cm−1 decreased significantly. ©1995 John Wiley & Sons, Inc.
Characterization and promotion of dilatation bands in toughenable thermosetting resins
Authors: Sue H.‐J. , Bertram J. L. , Garcia‐Meitin E. I. , Puckett P. M. 
Published: April 2003

AbstractFormation of dilatation bands has been found in a series of moderately crosslinked thermosets with molecular weights between crosslinks, Mc, ranging from 560 to 1000 g/mole. These dilatation bands, although they do not show distinct craze fibrils inside the band, do behave mechanically like the well‐known crazing phenomenon observed in polystyrene. Although the cause for the formation of dilatation bands is still largely unknown, the occurrence of the craze‐like fracture phenomenon (dilatation bands) is found to be strongly influenced by the stress state the matrix experiences, by the type of loading applied to the specimen, and by the type/size of toughener particles incorporated in the matrix. The tendency for dilatation band formation in engineering thermosets can be greatly enhanced by the use of craze‐prone toughener particles, such as nylon particles. The toughening effect via these newly observed dilatation bands is found to be quite impressive, and in some cases, can approach that via the shear‐banding process. The potential significance of the present finding for a better design of toughened thermosets for structural applications is discussed. ©1995 John Wiley & Sons, Inc.
Novel cellulose derivatives. III. Thermal analysis of mixed esters with butyric and hexanoic acid
Authors: Glasser Wolfgang G. , Samaranayake Gamini , Dumay Michelle , Davé Vipul 
Published: April 2003

AbstractCellulose derivatives with low degrees of substitution (i.e., DS < 1.5) often fail to reveal glass transition temperatures (Tg) by virtue of their tenacious adherence to moisture, thus preventing systematic analysis of substituent effects (size and DS) on Tg and Tm transitions. On the other hand, cellulose triesters have Tms that decline with acyl substituent size except when the substituent size becomes very large (i.e., > C6), and they have Tgs within 5–20°C of their Tms. This proximity is unusual for a semicrystalline material, and it interferes with the crystallization process that occurs between Tm and Tg. Triesters of cellulose with mixed acyl substituents (one smaller and one larger) allow not only unambiguous observation of Tgs and Tms but also an adjustable Δ(Tm − Tg) window that depends upon the size and the DS of the larger substituent. The materials studied including cellulose acetate butyrate triesters (DSbu 0.8–2.6), cellulose acetate hexanoate triesters (DShex 0–3.0), and cellulose acetate (DSac 2.44), revealed that only the mixed esters, in which the bulkier acyl group is in the range of DS 0.3–1.0, had a Δ(Tm − Tg) value in excess of 40°C. Although the Tm of cellulose acetate hexanoate declined by ca. 150°C per unit of DShex as DShex rose from 0 to 1, this was only ca. 25°C between DShex of 1 and 3. Frequently observed dual‐melt endotherms were attributed to two separate crystal morphologies. ©1995 John Wiley & Sons, Inc.
Thermal conductivity and thermal expansivity of thermotropic liquid crystalline polymers
Authors: Choy C. L. , Wong Y. W. , Lau K. W. E. , Yang Guangwu , Yee A. F. 
Published: April 2003

AbstractThe thermal conductivity and thermal expansivity of a thermotropic liquid crystalline copolyesteramide with draw ratio λ from 1.3 to 15 have been measured parallel and perpendicular to the draw direction from 120 to 430 K. The sharp rise in the axial thermal conductivity Kpar; and the drastic drop in the axial expansivity α∥ at low λ, and the saturation of these two quantities at λ > 4 arise from the corresponding increase in the degree of chain orientation revealed by wide‐angle x‐ray diffraction. In the transverse direction, the thermal conductivity and expansivity exhibit the opposite trends but the changes are relatively small. The draw ratio dependences of the thermal conductivity and expansivity agree reasonably with the predictions of the aggregate model. At high orientation, Kpar; of the copolyesteramide is slightly higher than that of polypropylene but one order of magnitude lower than that of polyethylene. In common with other highly oriented polymers such as the lyotropic liquid crystalline polymer, Kevlar 49, and flexible chain polymer, polyethylene, αpar; of the copolyesteramide is negative, with a room temperature value differing from those of Kevlar 49 and polyethylene by less than 50%. Both the axial and transverse expansivity show transitions at about 390 and 270 K, which are associated with large‐scale segmental motions of the chains and local motions of the naphthalene units, respectively. ©1995 John Wiley & Sons, Inc.
Solution viscosity behavior of complexes of poly(γ‐benzyl‐L‐glutamate) with lightly sulfonated polystyrene or its zinc salt
Authors: Shao L. , Weiss R. A. , Lundberg R. D. 
Published: April 2003

AbstractThe rheological behavior of solutions containing blends of poly(γ‐benzyl‐L‐glutamate) (PBLG) and either the free acid or the zinc salt of lightly sulfonated polystyrene (SPS) was studied as a function of blend composition, polymer concentration, degree of sulfonation of the SPS, and the polypeptide molecular weight. The zinc salt of SPS formed a transition metal complex with the amine‐end groups of the PBLG, and this resulted in an enhancement of the solution viscosity relative to a weighted average of the viscosities of the individual polymer solutions. The ZnSPS/PBLG solutions showed no anomalous time or shear dependencies. In contrast, solutions containing PBLG and the sulfonic acid derivative of SPS also had enhanced viscosities, but in addition, they exhibited time‐dependent viscosities (thixotropic behavior) and shear thickening (dilatant behavior). This was attributed to a nonequilibrium structure of the interpolymer complex due to a competition between acid‐amine and acid‐ester interactions. Although the acid‐amine interaction is enthalpically favored, when sufficient sulfonic acid groups were available, interactions between the sulfonic acid and the glutamate ester side groups of PBLG developed and this interaction promotes a helix‐to‐coil transition of the PBLG. ©1995 John Wiley & Sons, Inc.
Miscibility of poly(ε‐caprolactone), a semicrystalline polymer, with amorphous poly(styrene‐4‐hydroxystyrene) copolymers
Authors: Vaidya Milind M. , Levon Kalle , Pearce Eli M. 
Published: April 2003

AbstractThe miscibility of poly(ε caprolactone) (PCL) with poly(styrene‐co‐4‐hydroxystyrene) (PHS) copolymers was investigated as a function of comonomer composition experimentally and with calculations by two models; the binary interaction model and the association model. PCL was found to be completely miscible with PHS copolymers containing 5 or more mole percent of 4‐hydroxystyrene (HS) comonomer units for the entire range of blend compositions. Segmental interaction densities, Bijs, were determined by the analysis of the equilibrium melting point depression and by the application of the binary interaction model. By correlating the segmental interaction energy densities with the binary interaction model, thermodynamic miscibility is for comonomer composition over five mole percent of 4‐hydroxystyrene, which is in agreement with the experimental phase behavior. Application of the association model for specific interactions to blends also predicts the experimental miscibility boundary and phase behavior for all the PHS copolymers/PCL blends. © 1995 John Wiley & Sons, Inc.
Crowned polyacetylene. 2. cis form determination of poly(4′‐ethynylbenzo‐15‐crown‐5) by solid‐state NMR method
Authors: Kakuchi Toyoji , Matsunami Shigeyuki , Kamimura Hiroyuki , Ishii Fumiaki 
Published: April 2003

AbstractThe chain structure of cis‐poly(4′‐ethynylbenzo‐15‐crown‐5) (PEB15C5), prepared using the rhodium complex catalyst, was studied at −175°C using the solid‐state NMR technique. The second moment of PEB15C5 was 7.0 G2 for the main chain and 19.0 G2 for the side chain. These values agreed well with the respective theoretical ones for the cis form in the rigid state rather than the trans one. This agreement between experiment and theory suggested that the plane of the side chain (i.e., the benzo‐15‐crown‐5 group) is orthogonal to the main chain plane of the cis‐transoidal form. It was verified that the strong dipoledipole interaction between the side chains plays an important role as a clue to theoretically determine the cis‐transoidal form. NMR results in solid state confirmed theoretically that multipeaks in the 1H and 13C NMR spectra in CDCl3 solution are attributed to cis‐transoidal form in the chain. © 1995 John Wiley & Sons, Inc.
Phase‐matched second‐harmonic generation in poled polymer waveguide based on a main chain polymer
Authors: Tao X. T. , Watanabe T. , Zou D. C. , Shimoda S. , Usui H. , Sato H. , Miyata S. 
Published: April 2003

AbstractThe electric field‐induced dynamic phase‐matching of second harmonic generation (SHG) waveguide was demonstrated by using a main chain polyarylamine. The linear and nonlinear optical properties of this polymer are presented. The optimum phase‐matching thickness was controlled by applying an electric field to the polymer waveguide. The effective phase‐matching thickness variation induced by poling is about 0.025 μm that is six times larger than full width at the half‐maximum (FWHM) of phase‐matching thickness in conventional slab waveguide. The efficient phase‐matched SHG was observed from a taperless slab wave‐guide. The optical loss of poled polymer on glass substrate at 632.8 nm was 2.7 dB/cm. © 1995 John Wiley & Sons, Inc.
Hydrodynamic behavior of anionically prepared linear polyisoprenes and polystyrenes in carbon tetrachloride
Authors: Allorio Serena , Pispas Stergios , Siakali‐Kioulafa Ekaterini , Hadjichristidis Nikos 
Published: April 2003

AbstractIntrinsic viscosity, [η], weight‐average molecular weight, Mw, relationships are reported for narrow molecular weight distribution linear polyisoprene and polystyrene samples in CCl4 at 25°C. Molecular weight values cover a range nearly two orders in magnitude, extending as low as 3 × 103. In the case of polystyrene there exists a molecular weight range (around Mw = 16,700) corresponding to a change in the Mark‐Houwink‐Sakurada (MHS) exponent from α = 0.71 to α = 0.54. Comparisons between the viscometric and hydrodynamic radii, from literature data, are made. For polyisoprene the MHS relationship is reported in CCl4, for the first time. For this case α = 0.713 for the whole range of molecular weights studied. Values for the second virial coefficient from low‐angle light‐scattering measurements support the conclusions drawn from viscometry that CCl4 is a good solvent for both polymers studied. The different behavior of the MHS exponent may be attributed to the difference in chain flexibility. © 1995 John Wiley & Sons, Inc.