bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymorphism in alternating polyketones studied by x‐ray diffraction and calorimetry
Authors: Klop E. A. , Lommerts B. J. , Veurink J. , Aerts J. , Van Puijenbroek R. R. 
Published: April 2003

AbstractDifferential scanning calorimetry and high temperature x‐ray diffraction were used to study the perfectly alternating copolymer of ethene and carbon monoxide (polyketone; POKC2). It was found that oriented POK‐C2 fibers show a crystalline phase transition at a temperature between 110–125°C with a 10% change in crystalline density. At this temperature, the crystal structure reported recently (POK‐α) is transformed to a crystal structure that was reported in the past for room temperature imperfectly alternating polyketone. The latter structure will be designated as POK‐β. The influence of chain defects on the crystal structure was studied by synthesizing terpolymers (POK‐C2/C3), in which small amounts of propylene‐CO units are incorporated into the polymer backbone. The resulting terpolymers differ from the copolymer by the presence of methyl groups randomly distributed along the polyketone backbone chain. Evidence is presented that indicates that the methyl groups are built into the crystal lattice as defects. With more than 5 mole‐% propene the terpolymer fibers crystallize exclusively in the β‐modification. Below this level the α/β ratio (at room temperature) increases with decreasing amounts of propene. Both as‐synthesized and as‐spun POK‐C2 were found to consist of both POK‐α and POK‐β; the α/β ratio depends on the method of preparation. Because the drawn POK‐C2 fibers studied here consist exclusively of POK‐α, the process of spinning and drawing leads to the transformation of unoriented β‐rich material into oriented POK‐α. © 1995 John Wiley & Sons, Inc.
Local chain motions of poly(β‐hydroxyoctanoate) in the bulk. 13C NMR relaxation study
Authors: Spyros A. , Dais Photis , Marchessault R. H. 
Published: April 2003

AbstractVariable‐temperature 13C NMR spin‐lattice relaxation times (T1) and Nuclear Overhauser Enhancements (NOE) at two magnetic fields have been used to study the dynamics of the amorphous part of a semicrystalline sample (33% of crystallinity) of poly(β‐hydroxyoctanoate) (PHO). The interpretation of the relaxation data of the backbone carbons was made by employing a number of motional models. Among these, the DLM model offered the best interpretation of the relaxation data in terms of conformational transitions and librational motions of the backbone CH vectors, and proved to be superior to unimodal distribution functions. The interpretation of temperature‐ and frequency‐dependent T1 and NOE data of the carbon nuclei in the n‐pentyl side chain was made by employing a newly developed composite spectral density function for multiple internal CC bond rotations of restricted amplitude and chain segmental motion. The temperature dependence of the linewidths of the various protonated carbon resonances of PHO has been discussed in terms of the semicrystalline character of this polymer. © 1995 John Wiley & Sons, Inc.
NMR studies of water in polyimide films
Authors: Li S. Z. , Chen R. S. , Greenbaum S. G. 
Published: April 2003

AbstractCommercial polyimide films containing up to ∼ 3 wt % water have been studied by proton, deuteron, and oxygen‐17 nuclear magnetic resonance (NMR). Comparisons between NMR results and previous dielectric relaxation (DR) results for a variety of Kapton films show that there is a one‐to‐one correspondence between specific dielectric loss peaks and features of the 2H or 17O NMR spectra. It is concluded that water molecules, which interact only weakly with the polymer, reside in the polyimide matrix in two configurations, randomly oriented single molecules and chains of water molecules oriented perpendicular to the plane of the film. The correspondence between NMR and DR observed in water in Kapton extends to water in Upilex and to methanol and acetic acid in Kapton. © 1995 John Wiley & Sons, Inc.
NMR characterization of styrene‐divinylbenzene gel beads using freezing point depression of benzene
Authors: Ogino Kenji , Sato Hisaya 
Published: April 2003

AbstractFreezing processes of benzene in the presence of styrene‐divinylbenzene gel beads were investigated by proton nuclear magnetic resonance spectroscopy. Some portion of benzene in the pore did not freeze below its freezing point, which was detected until −80°C. Temperature dependence of the amount of unfrozen benzene was discussed in relation to the pore size and the cross‐linking density of gel beads. The small pore size and high crosslinking density increased the amount of unfrozen benzene, whereas the polymer matrix concentration showed little effect on the freezing processes. © 1995 John Wiley & Sons, Inc.
Structure and properties of a photosensitive polyimide: Effect of photosensitive group
Authors: Ree Moonhor , Nunes Thomas L. , Chen K.‐J. Rex 
Published: April 2003

AbstractThe photosensitive poly(p‐phenylene biphenylteracarboximide) (BPDA‐PDA) precursor was synthesized by attaching photocross‐linkable 2‐(dimethylamino)ethyl methacrylate (DMAEM) monomer to its poly(amic acid) through acid/base complexation. The polyimide thin films were prepared by a conventional cast/softbake/thermal imidization process from the photosensitive precursors with various concentrations of DMAEM. The structure and properties of the polyimide films were investigated by small‐angle and wide‐angle x‐ray scattering, refractive indices and birefringence analysis, residual stress and relaxation analysis, stress‐strain analysis, and dynamic mechanical thermal analysis. In comparison with the polyimide film from the poly(amic acid), the films, which were imidized from the photosensitive precursors, exhibited a better molecular order and microstructure; however, they exhibited less molecular orientation in the film plane. Despite the enhancement in both the molecular order and microstructure, the film properties (i.e., mechanical properties, thermal expansion, residual stress, optical properties, dielectric constant, and water sorption) degraded overall due to both the decrease in molecular in‐plane orientation and the formation of microvoids caused by the bulky photosensitive group during thermal imidization. That is, on one hand, the PSPI precursor formation provides an advantageous, direct patternability to the BPDA‐PDA precursor, and on the other hand, it results in degraded properties to the resulting polyimide film. © 1995 John Wiley & Sons, Inc.
Gas transport properties of polymers based on spirobiindane bisphenol
Authors: Pessan L. A. , Koros W. J. , Schmidhauser J. C. , Richards W. D. 
Published: April 2003

AbstractTransport properties of pure gases in polycarbonates, polyesters, and polyetherimides based on 6,6′‐dihydroxy‐3,3,3′,3′‐tetramethyl‐1,1′‐spiro biindane (SBI) and bisphenol‐A (BPA) are compared at 35°C. The SBI monomer contains two spiro‐linked five‐membered rings which are fused to the phenyl rings at the meta and para positions to the hydroxyl groups. This molecular structure gives SBI‐based polymers with higher fractional free volume (FFV) and lower intramolecular motions as compared to the BPA‐based analogs. The inhibition of chain packing due to the SBI moiety yields polymers with much higher permeabilities for all the gases studied, despite the hinderance of mobility associated with the SBI structure. Simultaneous increase in selectivity was also observed for some gas pairs. Oxygen permeabilities up to 5.9‐fold higher with increases of up to 13% in O2/N2 selectivities were observed for a polyester based on SBI as compared to its analog based on BPA. Higher permeabilities of up to 4.3‐fold for He and up to 4.8‐fold for CO2 were observed due to the substitution of SBI for BPA. Not surprisingly, lower values of He/CH4 and CO2/CH4 selectivities were obtained for the more open SBI‐containing polymers. The changes in fractional free volume and inhibition of small‐scale mobility for some materials caused by the SBI moiety were measured and used in the interpretation of the gas transport properties. The individual contributions of diffusivity and solubility to the overall transport behavior of the polymers are discussed and correlated to the structural alterations caused by the SBI substitution for BPA monomer. © 1995 John Wiley & Sons, Inc.
Star‐shaped polymers by living cationic polymerization. VIII. Size and shape of star poly(vinyl ether)s determined by dynamic light scattering and computer simulation
Authors: Kanaoka Shokyoku , Sawamoto Mitsuo , Higashimura Toshinobu , Won Jongok , Pan Chuanbin , Lodge Timothy P. , Fujiwara Masaaki , Hedstrand David M. , Tomalia Donald A. 
Published: April 2003

AbstractThe sizes and shapes of star‐shaped poly(vinyl ether)s, prepared by living cationic polymerization, were studied by dynamic light scattering and molecular mechanics‐based computer simulation. The hydrodynamic radii (Rh) of star poly(isobutyl vinyl ether)s (4a; M̄w = 2.2 × 104 − 1.7 × 105) determined by dynamic light scattering were in the range from 30 to 90 Å in tetrahydrofuran or ethyl acetate. Consistent with the expected multiarmed architecture of 4a, the radius for a given number (f) of arms per molecule increased with the degree of polymerization [DP(arm)] of the arms, and for a fixed DP(arm), the radius increased with f. The relationship between arm number f and the “shrinking” factor h [Rh(star)/Rh(linear)] was consistent with multibranched structures for the star polymers. These results are supported by those for the molecular weight itself; the apparent weight‐average molecular weights by size‐exclusion chromatography are less than the corresponding absolute values by static light scattering. The dependence of h on f suggests some degree of asymmetry in the star shape. Similar results were also obtained by the computer simulation of potential energy‐minimized conformations of the arms, which implied almost spherical but slightly asymmetric shapes. The computer simulation also demonstrated that the star polymer (4b) with pendant hydroxyl groups in the arms is smaller in size than the corresponding alkyl (isobutyl) (4a) with the identical arm number and arm degree of polymerization. © 1995 John Wiley & Sons, Inc.
Isotope and pressure effects in polymer solutions. Demixing of polystyrene(h/d) poly‐2‐chlorostyrene blends
Authors: Zywocinski Andrzej , Wieczorek Stefan A. , Van Hook W. Alexander 
Published: April 2003

AbstractLiquid‐liquid demixing, following spinodal quenches of poly‐2‐chlorostyrene/polystyrene blends, was followed by light scattering at 632.8 nm. The dependences of demixing on H/D substitution and molecular weight of the polystyrene, and on pressure, are reported. In the region of interest, the phase diagram is of the lower critical solution (LCS) type, and demixing is induced by raising the temperature. The transition temperature is lowered by deuterium substitution. At constant quench depth the transition proceeds more rapidly at elevated pressure. © 1995 John Wiley & Sons, Inc.
The effect of aryl nitration on gas sorption and permeation in polysulfone
Authors: Ghosal Kanchan , Chern Rey T. , Freeman Benny D. , Savariar Raj 
Published: April 2003

AbstractCO2, CH4, O2, and N2 permeability and solubility of unmodified and aryl‐nitrated polysulfone were determined at 35°C and pressures up to 20 atm. The degree of nitration was varied from 0 to 2 nitro groups per repeat unit. The permeability and diffusion coefficients for all gases decreased with increasing degree of nitro substitution. The decrease in gas diffusivity is attributed to a combination of decreased fractional free volume and decreased torsional mobility with increasing degree of substitution. The solubilities of N2, O2, and CH4 do not show a systematic dependence on degree of substitution. However, CO2 solubility apparently goes through a minimum as the degree of substitution is increased. CO2 solubility may be influenced by a competition between increases in polymer polarity (favoring higher solubility) and lower free volume (favoring lower solubility) that accompanies increases in the polar nitro substituent concentration. CO2/CH4 solubility selectivity increases monotonically as the degree of substitution increases. CO2/CH4 permselectivity and diffusivity selectivity increased with increasing degree of substitution. © 1995 John Wiley & Sons, Inc.
Block copolymers as compatibilizers for blends of linear low density polyethylene and polystyrene
Authors: Li T. , Topolkaraev V. A. , Hiltner A. , Baer E. , Ji X. Z. , Quirk R. P. 
Published: April 2003

AbstractCompatibilization of blends of linear low‐density polyethylene (LLDPE) and polystyrene (PS) with block copolymers of styrene (S) and butadiene (B) or hydrogenated butadiene (EB) has been studied. The morphology of the LLDPE/PS (50/50) composition typically with 5% copolymer was characterized primarily by scanning electron microscopy (SEM). The SEB and SEBS copolymers were effective in reducing the PS domain size, while the SB and SBS copolymers were less effective. The noncrystalline copolymers lowered the tensile modulus of the blend by as much as 50%. Modulus calculations based on a coreshell model, with the rubbery copolymer coating the PS particle, predicted that 50% of the rubbery SEBS copolymer was located at the interface compared to only 5–15% of the SB and SBS copolymers. The modulus of blends compatibilized with crystalline, nonrubbery SEB and SEBS copolymers approached Hashin's upper modulus bound. An interconnected interface model was proposed in which the blocks selectively penetrated the LLDPE and PS phases to provide good adhesion and improved stress and strain transfer between the phases. © 1995 John Wiley & Sons, Inc.
Microwave frequency dielectric properties of poly(vinylidene fluoride) films
Authors: Osaki Shigeyoshi 
Published: April 2003

AbstractThe frequency dependence of dielectric constant ϵ′, dielectric loss ϵ″, and dielectric anisotropy were determined for poly(vinylidene fluoride) (PVDF) in microwave frequencies from 4 to 13 GHz. The ϵ′ and ϵ″ for PVDF films decreased with increasing frequency. Both ϵ′ and ϵ″ were larger in the transverse direction than in the machine direction or draw direction, but the values at 12 GHz were smaller than those observed at 4.0 GHz. The angular dependence of ϵ″ at microwave frequency reflects the orientational distribution of molecules in the amorphous region. The orientation function was determined to be about 0.04 and 0.01 for uniaxially and biaxially stretched PVDF, respectively. © 1995 John Wiley & Sons, Inc.
Structural characterization of polypyrrole in the solid state by high resolution 15N NMR spectroscopy [II]
Authors: Kurosu Hiromichi , Kikuchi Mizuyo , Ando Isao 
Published: April 2003

AbstractThe solid‐state 15N CP/MAS NMR spectra and 15N spin‐lattice relaxation times (T1) of doped and dedoped 15N‐labeled polypyrroles prepared by electrochemical polymerization, have been measured by means of high‐resolution solid‐state 15N NMR. The 15N signal of polypyrrole consists of four peaks decomposed by line shape analysis. The four peaks obtained have been assigned to the various structures of polypyrrole. Further, the half‐width of the 15N NMR spectra of polypyrroles is discussed as related to the electrical conductivity. © 1995 John Wiley & Sons, Inc.
Heat capacity of water in poly(methyl methacrylate) hydrogel membrane for an artificial kidney
Authors: Ishikiriyama Kazuhiko , Todoki Minoru 
Published: April 2003

AbstractThe heat capacities of a poly(methyl methacrylate) hydrogel membrane for an artificial kidney have been determined over the range of temperatures from 228 to 298 K as a function of water content. At least two kinds of water were found: freezable water and nonfreezable water. The partial specific heat capacities of both waters were calculated from the dependence of heat capacity of the hydrogel on the water content. The heat capacities of freezable water were estimated to be 1.04 cal g−1 K−1 at 298 K and 0.47 cal g−1 K−1 at 228 K. The mobility must therefore be similar to that of bulk water at 298 K, though the melting temperature was lower than that of bulk water. Consequently, the freezable water was not assigned to bound water but to pore water for which the melting temperature was depressed due to interfacial tension. On the other hand, the heat capacities of nonfreezable water were estimated to be 1.02 cal g−1 K−1 at 298 K and 1.06 cal g−1 K−1 at 228 K. The mobility of the water would be similar to that of free water at both 298 and 228 K. © 1995 John Wiley & Sons, Inc.
Elastic and quasielastic light scattering from mixtures of three polymers and a solvent: The effects of polymethylmethacrylate concentration and molecular weight on the properties of polystyrene/polydimethylsiloxane/toluene solutions
Authors: Strazielle Claude , Duval Michel , Benmouna Mustapha 
Published: April 2003

AbstractElastic and quasi‐elastic light scattering data obtained from PS/PDMS/PMMA/toluene mixtures are reported. Several systems characterized by different concentrations and different molecular weights of PMMA are considered. For each of these systems, a systematic investigation is performed as a function of the scattering angle and the concentration of the PS/PDMS mixture using both techniques. The PMMA does not contribute directly to the scattered light since its increment of refractive index is zero. However the data show that its presence modifies substantially the apparent interaction parameter of PS and PDMS and the single diffusion coefficient of these polymers in the solution. The variations of these quantities with the concentration and molecular weight of PMMA are obtained. The data are analyzed within a simplified model combining based on the random phase approximation and the Rouse dynamics for ternary polymer mixtures. © 1995 John Wiley & Sons, Inc.
Long‐chain branching in free‐radical polymerization due to chain transfer to polymer
Authors: Tobita Hidetaka , Hatanaka Koji 
Published: April 2003

AbstractThe Monte Carlo sampling technique is used to investigate the branched structure formation during free‐radical polymerization that involves chain transfer to polymer. This method accounts for the history of the generated branched structure and can provide virtually any structural information, because one can observe each polymer molecule directly. In this paper, we investigate the whole molecular weight distribution (MWD) for both pre‐ and postgelation periods, the MWDs for polymer molecules containing 0, 1, 2, 3, … branch points, the branching density of polymer molecules as functions of both size and the number of branch points, the spatial distribution of the branched chains at the theta state, etc. Contrary to the term ‘long‐chain’ branching, many branch chains are relatively small, and the branched structures formed are significantly different from those usually depicted to introduce ‘branched polymers’ in many introductory textbooks. The radii of gyration at the theta state can be approximated by the Zimm‐Stockmayer equation for random branching, in spite of various violations against the assumptions used in deriving the equation © 1995 John Wiley & Sons, Inc.
Role of polyester resin on the epoxy matrix system
Authors: Mukherjee G. S. , Saraf M. N. 
Published: April 2003

AbstractInterpenetrating polymer network (IPN) as a polymer blend matrix was prepared using different ratios of polyester (PE) to epoxy (E) resins. It was observed that 11.33 wt % PE in the blend provides maximum mechanical properties, particularly the modulus for the casting, and such a blend is referred to as “optimum casting” (OC). The density of the blends containing up to 11.33% PE, especially of OC, was found to have increased by the presence of PE in the E network significantly more than would have been estimated from the calculation based on the rule of additivity. The thermal expansion coefficient parameter (Δαi) of the OC was found to be 2.68 × 10−4K−1. The scanning electron micrograph (SEM) of the fracture surface of OC only showed a glass‐like smooth surface. The change in the mechanical properties due to the varying proportions of PE in the blend was studied critically on the basis of failure mechanisms and morphological features. The differential thermogravimetric analysis (DTGA) of OC indicated only one peak in spite of the presence of two resin constituents, whereas castings with an excess of PE in the blend showed multiple peaks. Interestingly, as far as the DTGA is concerned, a domain of seemingly OC origin was found to remain, even in the blends containing PE resin above its optimum level (> 11.33 wt %). ©1995 John Wiley & Sons, Inc.
Properties of an amphoteric cellulose derivative containing anionic carboxymethyl and cationic 2‐hydroxy‐3‐(trimethylammonio) propyl substituents
Authors: Zheng Guo‐Zhen , Meshitsuka Gyosuke , Ishizu Atsushi 
Published: April 2003

AbstractAn amphoteric cellulose derivative, O‐carboxymethyl‐O‐2‐hydroxy‐3‐(trimethylammonio) propylcellulose (CM‐HTMAPC), was prepared by the etherification of O‐carboxymethylcellulose (CMC) with (3‐chloro‐2‐hydroxy‐n‐propyl)‐trimethylammonium chloride in a NaOH solution. Apparent molecular sizes of the amphoteric cellulose derivative in aqueous solutions of different NaCl concentrations under various pH conditions were investigated by gel permeation chromatography (GPC), and results were evaluated in terms of inter‐ and intramolecular ionic interactions. Relation between GPC and viscosity results was also discussed. A titration method to determine the apparent acidic dissociation constants of carboxymethyl substituents was developed and the effect of cationic substituents on apparent acidic dissociation constants was examined. ©1995 John Wiley & Sons, Inc.
Holographic grating relaxation studies of probe diffusion in amorphous polymers
Authors: Xia Jiulin , Wang C. H. 
Published: April 2003

AbstractProbe diffusion of camphorquinone, thymoquinone, and diacetyl in polymers was studied by the laser‐induced holographic grating relaxation (HGR) technique in polymers. The effects of changing the probe size and various parameters of the polymer, such as the molecular weight, chain conformation, and the glass transition temperature, on the probe diffusion coefficient have been investigated. Furthermore, effects of cross‐linking and plasticizing the chains of the polymer host on the probe diffusion coefficient were also studied. Temperature‐dependent studies show that except for the very low molecular weight poly(methyl methacrylate), all probe diffusion coefficient data above the glass transition temperature fit well to the WLF equation. ©1995 John Wiley & Sons, Inc.
Unique crystalline structure and performance of poly(ethylene terephthalate) melt spun fibers
Authors: Zhou Qiang , Wu Gang , Tucker Paul A. , Cuculo John A. 
Published: April 2003

AbstractModification of the threadline dynamics has effected significant alternations in the structure and improvements in the properties of high‐speed melt spun poly(ethylene terephthalate) (PET) fibers. Key process parameters extant in the threadline dynamics, such as temperature, tensile stress, and deformation time, were independently controlled through proper implementation of on‐line perturbations. The placement of a liquid isothermal bath in close proximity to the spinneret in the melt spinning threadline provided tremendous increase in the spinning stress while at the same time controlled the filament temperature corresponding to development of the desired fiber structure. Characterization of the fiber structure and physical properties has been carried out using birefringence measurements, density, shrinkage, x‐ray diffraction, DSC, FTIR spectroscopy, and tensile tests. The results provided sufficient evidence to support the existence of a unique crystalline morphology that led to the significantly improved tensile properties and excellent dimensional stability of the resulting fibers. This unique crystalline morphology was typically characterized by the presence of a larger amount of extended chain segments and an enhanced molecular connectivity. ©1995 John Wiley & Sons, Inc.