bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular interactions in polystyrene cosolvent systems
Authors: Parmer Jerome F. , Porter Roger S.
Published: April 2003

Studied here are miscible binary cosolvents for polystyrene, for which polystyrene is insoluble in either of the individual solvents. Polymer‐solvent interactions in solutions of atactic polystyrene in acetone/diethyl ether and in methylcyclopentane (MCP)/acetone binary cosolvents have been investigated using nuclear magnetic resonance (NMR) spectroscopy. Polystyrene 13C chemical shifts were measured as a function of miscible binary solvent compositions and temperature. The NMR data were used to calculate “association constants” as a measure of specific interactions of the solvent components with all sites on the polymer. In mixtures of acetone and diethyl ether, 13C‐NMR indicates a weak interaction between the polystyrene phenyl ring and the diethylether solvent component. In the polystyrene/MCP/acetone system, present NMR data reveal no preferential interactions. Additional NMR measurements were performed on polystyrene in mixtures of CCl4/acetone. From these results, it is concluded that although preferential polymer‐solvent interactions are present in some cosolvent systems, they are not a prerequisite for such behavior.
Permeation of carbon dioxide through homogeneous dense and asymmetric cellulose acetate membranes
Authors: Sada E. , Kumazawa H. , Yoshio Y. , Wang S.‐T. , Xu P.
Published: April 2003

Sorption isotherms for carbon dioxide in a homogeneous dense cellulose acetate membrane were measured by the pressure decay method at three temperatures between 20 and 40°C and gas pressures up to 1.7 MPa. Steady‐state permeation rates for the same system at three temperatures between 24 and 40°C and gas pressures up to 2.2 MPa were measured by the variable volume method. The equilibrium sorption was described well in terms of the dual‐mode sorption model. The pressure dependence of the mean permeability coefficient was interpreted by the total immobilization model, i.e., a limiting case of the dual‐mode mobility model, where the diffusion coefficient for the Henry's law mode is not assumed to be constant but depends upon gas pressure via a modified free‐volume theory. The observed pressure dependence of the mean permeability coefficient through an asymmetric cellulose acetate membrane was very similar to that through a homogeneous dense membrane. The thin skin layer in the asymmetric membrane can be simulated by a homogeneous dense membrane from the point of view of gas sorption and diffusion.
Selective adsorption to cellulose in cadoxen solution
Authors: Huglin Malcolm B. , O'Donohue Stephen J. , Sasia Pedro M.
Published: April 2003

Refractive index and density increments at constant composition and also at constant chemical potential have been measured on solutions of cellulose in alkaline aqueous cadoxen. Apparent and true molecular weights of cellulose in this solvent have been determined by light scattering. The findings indicate that [Cd(en)3]2+ ions are preferentially adsorbed to the polymer to the average extent of two ions per three anhydroglucose subunits. Molecular models have shown that this effect is feasible sterically. In cadoxen alone the specific conductance increased with increasing concentration of cadmium and, for a fixed cadmium concentration, the specific conductance was observed to decrease with increasing concentration of dissolved cellulose. This was attributed to reduced overall ionic mobility resulting from selective adsorption of complex cadmium ions to the polymer chain. An analysis has been proposed to quantify this interaction.
The liquid‐crystalline properties of selected cellulose derivatives
Authors: Pawlowski Walter P. , Gilbert Richard D. , Fornes Raymond E. , Purrington Suzanne T.
Published: April 2003

The liquid‐crystalline properties of three cellulose esters, phenylacetoxy cellulose (PAC), 4‐methoxyphenylacetoxy cellulose (4MPAC), and p‐tolylacetoxy cellulose (TAC) and two cellulose silyl ethers, trimethyl silyl cellulose (TMSC) and t‐butyldimethylsilyl cellulose (TBDMSC), are reported.

Hot‐stage polarized light microscopy provided evidence regarding the formation of thermotropic mesophases in the PAC, 4MPAC, TAC, and TMSC in bulk form upon heating. The concomitant DSC data showed further evidence of the thermotropic nature of these materials.

PAC, 4MPAC, TAC, and TMSC formed lyotropic mesophases at 44, 48, 50, and 27 wt%, respectively in CH2Cl2. The presence of fingerprint patterns in wholly anisotropic solutions in conjunction with optical rotation measurements confirmed the cholesteric nature of these liquid crystalline solutions. TBDMSC formed neither a lyotropic nor a thermotropic liquid‐crystalline phase due to the low degree of substitution (DS 0.68) of this derivative. The hydroxyl substituents of PAC, 4MPAC, TAC, and TMSC may be readily removed under mild conditions to regenerate cellulose.
Adhesive interface interactions between primary aliphatic amine surface conditioners and polyamic ester/polyimide resins
Authors: Linde H. G.
Published: April 2003

The interface reactions of 3‐aminopropyltriethoxysilane treated surfaces, with a polyamic alkyl ester/polyimide resin formed from pyromellitic dianhydride and oxydianiline, were defined by Fourier Transform Infrared (FTIR) analysis on the surface layers of germanium internal reflection plates. Adhesion between these interfacial layers is the result of chemical bonding, which apparently proceeds through initial amide formation between the amino function of the silylated surface and the alkyl ester group present in the polyamic ester. Heating results in diamide formation by a second alkyl, surface‐bound amine displacing the aromatic polymer amine. Heating the more stable dialkyldiamide to 300°C imidizes both the polymer and the interfacial region, producing a strong laminate composite. Polymer scission at the aromatic amide linkages occurs in this adhesion process, bonding surface‐bound alkyl amines to one end of a shortened polymer chain.
Polymer degradation during combustion
Authors: Brauman S. K.
Published: April 2003

A novel driven‐rod, radiant pyrolysis technique has been used to study the steady‐state linear regression of vertically mounted poly(methyl methacrylate) and polypropylene rods degrading from the top under high‐flux, nonflaming conditions that simulate those of combustion. With this technique reliable temperature‐depth and oxygen‐depth profiles have been obtained and used to calculate the observed mass loss rates and to elucidate the mode of polymer degradation during combustion, respectively. For poly(methyl methacrylate) burning in this rod configuration, condensed phase oxidation is unimportant and the degradation mechanism is similar to that under more conventional slow‐heating conditions in the absence of air. In contrast, for burning polypropylene condensed phase oxidation occurs; the lack of oxygen incorporation suggests that the polymer degrades by oxygen‐promoted pyrolysis.
Chemiluminescence studies of the thermooxidation of PEEK
Authors: Brauman S. K. , Pronko J. G.
Published: April 2003

A highly sensitive microcomputer‐controlled chemiluminescence apparatus capable of spectral resolution of emitted light has been used to study the oxidation of thermoplastic matrix material poly(ether ether ketone), PEEK, at 110°C in oxygen. Even after prolonged exposure and extensive decay in the chemiluminescence signal, the samples show no change in properties or accumulation of oxidation products. Evidence suggests that after oxygen‐assisted initiation, reaction proceeds by radical transfer primarily of polymer phenoxy radicals in a type of radical aromatic substitution reaction on PEEK. Similar substitution‐type biomolecular termination of polymer phenoxy radicals can lead to excited polymer and benzoquinone, emitters that account for much of the oxyluminescence spectrum of PEEK. Under the experimental conditions, the benzoquinone is volatile and the product polymer should be indistinguishable from starting polymer.
Hole transport in polymers of (N‐ethylcarbazol‐3‐yl) methyl acrylate and methacrylate
Authors: Uryu Toishiyuki , Ohkawa Haruki , Oshima Ryuichi
Published: April 2003

(N‐Ethylcarbazol‐3‐yl)methyl acrylate and methacrylate were polymerized anionically and radically. Anionically‐polymerized polyacrylate using ethylmagnesium chloride‐benzalacetophenone as catalyst is an isotactic rich polymer with 85% isotactic dyad. All polymers except anionically polymerized polymethacrylate showed good film forming property. Hole drift mobilities measured by the time‐of‐flight method at room temperature and at 5 × 105 V/cm are in the following order: isotactic polyacrylate (1.0 × 10‐5 cm2/V s) > atactic polyacrylate (1.8 × 10‐6 cm2/V s) > atactic polymethacrylate (1.2 × 10‐6 cm2/V s) at 5 × 105 V/cm. These results are discussed in terms of the hopping model between localized sites.
Role of negative ions in the RF plasma deposition of fluoropolymer films from perfluoropropane
Authors: Haque Yasmeen , Ratner Buddy D.
Published: April 2003

RF plasma‐deposited fluoropolymer films prepared from perfluoropropane were examined on a variety of metallic, glass, and polymeric substrates using electron spectroscopy for chemical analysis (ESCA) and Fourier transform infrared spectroscopy (FTIR). The F1s ESCA spectra of thin (< 100 Å) depositions on some substrates exhibited a peak suggestive of ionic fluoride species. FTIR studies demonstrated the presence of bifluoride ion in some films. Angular‐dependent ESCA studies indicated that these ionic species were not located at the outermost surface of the deposition but rather near the fluoropolymer‐substrate interface. By depositing these fluoropolymer films on a large number of different metallic substrates, and comparing the results of thermal stability studies and solubility studies with literature descriptions of the properties of each of the respective fluoride salts, additional support for the identification of ionic fluoride species at the fluoropolymer‐substrate interface was generated. The implications of this interfacial ionic zone for the adhesion of plasma‐deposited fluoropolymer films to substrates are considered.
Synthesis and characterization of ring polybutadienes
Authors: Roovers J. , Toporowski P. M.
Published: April 2003

It has been shown that butadiene initiated with potassium naphthalene in the mixture THF‐n‐hexane polymerizes conveniently rapidly. The active center is sufficiently stable below 0°C to produce narrow molecular weight linear polybutadiene. The two‐ended living polymer has also served to prepare ring polybutadienes. The analysis of the ring polymers by a high‐resolution set of SEC columns proved superior to the conventional method for the determination of the linear content in rings and in synthetic mixtures of rings and linear polymers. Dilute solution characterization of the linear and ring polymers shows that gr′ = [η]/r[η]l is less than 0.66 in a good solvent.
Sorption and transport properties of MY720/DDS epoxy reacted with blocking reagents
Authors: Kelly B. K. , Gilbert R. D. , Fornes R. E. , Stannett V. T.
Published: April 2003

Thin films of the epoxy formed by the reaction of tetraglycidyl 4,4'‐diamino‐diphenylmethane and 4,4'‐diaminodiphenyl sulfone (73:27 w/w) were reacted with acrylonitrile (ACN) and isocyanates as blocking reagents for hydroxyl, amine, and epoxy groups. The water uptake at 30, 45, 55, and 70°C of the epoxy resin was monitored gravimetrically. At each temperature the epoxy exhibited case I or Fickian behavior. The diffusion coefficient D increased from 30 to 55°C, but decreased at 70°C because of the reaction of water with residual oxirane groups. Diffusion of ACN is accompanied by both reaction and polymerization, so equilibrium could not be reached. Sorption of the isocyanates essentially follows case I or Fickian behavior. Equilibrium moisture absorptions showed a correspondence between the reduction of moisture absorption and the number of blocked functional groups, irrespective of the nature of the blocking groups. Moisture absorption reductions as high as 68% were obtained. Moisture diffusion of the films after blocking with the various reactants exhibits case I or Fickian behavior. At 30°C, D values are significantly higher for reacted films. At 70°C, the value of D is unchanged as compared with the 30°C value for films reacted with ACN, but D values are significantly lower for films reacted with isocyanate blocking reagents as compared with the epoxy resin.
Mechanical instability of amorphous polymeric networks: Asymmetric deformation under symmetric biaxial tension
Authors: Erman Burak
Published: April 2003

Asymmetric deformation of a symmetrically loaded rubber sheet was observed, many years ago, by Treloar in his experiments on natural rubber. The problem has recently been studied by Kearsley, and the possibility of asymmetric deformations in an equi‐biaxial state of force is predicted by the use of phenomenological constitutive relations. In the present study, the problem is analyzed in relation to the molecular constitution of rubber networks. It is shown that mechanical instability in symmetrically loaded networks may be possible only for limited choices of molecular parameters such as junction functionality, degree of crosslinking, and the degree of swelling during crosslinking and during deformation. Stability of multiple valued deformations is discussed by thermodynamic considerations of the elastic potential.
Computer simulation of polymeric materials. I. Stress‐strain behavior
Authors: Cook Robert
Published: April 2003

A model of polymeric materials has been developed that includes many of the features of condensed‐phase polymer chain dynamics, central among them chain relaxation via conformational motion. The model consists of a number of chains of particles that are connected by bonds with multiwelled potentials to approximate the energetics of conformational motion. Interactions between particles on adjacent chains are modeled by short range repulsive potentials. We have examined the stress‐strain behavior of the model using molecular dynamics simulations and find qualitative agreement with the observed experimental behavior of polymeric materials.
Dynamic mechanical relaxations of polyterephthalates based on trimethylene glycols
Authors: Carlos González César , Pereña José Manuel , Bello Antonio
Published: April 2003

The dynamic mechanical relaxations of poly(trimethylene glycol terephthalate) (PTMT), poly(ditrimethylene glycol terephthalate) (PDTMT) and two copolymers obtained from them have been studied between − 150 and 200°C with a dynamic viscoelastometer. The four polymers show three relaxations that are designated α, β, and γ in order of decreasing temperature. The α relaxation is considered to be the glass transition of the polymers. The β relaxation is wider and weaker than the α, as normally occurs in the polyester series. The γ relaxation takes place at temperatures below − 100°C and is usually overlapped by the β relaxation. The influence of thermal and mechanical histories on the nature, location, and intensity of the three relaxations is studied and discussed.
A dielectric study of poly(ethylene‐co‐vinyl acetate)‐poly(vinyl chloride) blends. III. Direct current conductivity and electrode polarization
Authors: Rellick G. S. , Runt J.
Published: April 2003

The large direct current (d.c.) conductance observed at low frequencies and high temperatures in conjunction with a simple electrical circuit model was used to calculate specific conductivities in PVC and mixtures of PVC with a poly(ethylene‐vinyl acetate) copolymer. Activation energies for d.c. conduction and dipole relaxation in PVC and the blends were found to be in reasonable correspondence. The effects of different electrode materials on the d.c. conductance as well as on electrode polarization are discussed.
High‐energy ion implantation of polymers: Poly(vinylidene fluoride)
Authors: Said M. A. , Balik C. M. , Carlson J. D.
Published: April 2003

Poly(vinylidene fluoride) films were implanted with high‐energy (up to 6 MeV) He, C, O, and Ni ions and characterized using DSC, FTIR, and solubility measurements. None of the ions were energetic enough to penetrate the polymer film completely. The effects of ion energy, fluence, and ion type were studied individually. The implantation process lowered the crystallinity, induced crosslinking, and produced carbonyl groups on the polymer. The ion energy (in the range 0.4–4.5 MeV for He ions) had the most drastic effect, the radiation damage was found to increase with decreasing energy. The sample implanted with 0.4 MeV He ions lost 81% of its initial crystallinity and was only 24% soluble, even though the incident ions have a range of only 2.7 μm in this case. The other samples retained most of their initial crystallinity but still were substantially cross‐linked. The results can be qualitatively explained by assuming that hydrogen free radicals, produced during implantation, can diffuse throughout the sample and react, resulting in crystallinity and solubility losses beyond the ion deceleration region.
Effect of heating and aging on microstructure of polyester‐polyamide copolymer
Authors: Lefelar J. A.
Published: April 2003

Polyester‐polyamide (PET/PA) copolymers offer a wide range of possible applications where both dimensional stability and good impact resistance can be achieved from their synergism. In order to ensure these properties for long‐term use, however, problems of phase separation, volume change, and chemical reequilibration on heating or aging must be identified and overcome. Wide‐angle x‐ray diffraction (WAXD), small‐angle x‐ray scattering (SAXS), and thermal analysis were employed to follow the microstructure of a 70:30 PET/PA copolymer with several different processing histories as a function of heat history and both short‐term and long‐term aging. Heating the copolymer, as received, above the melting temperature of PET caused phase mixing. The effect of heating on crystallinity depended on starting crystallinity. Holding the copolymer at 50°C, just below the glass transition temperature of PET, caused phase separation in samples which had been annealed for 30 min at 150°C. On long‐term aging samples gave evidence of phase mixing. The results indicate highly nonequilibrium structure in the material, regardless of the original processing.
Synthesis and properties of poly(1,2–8,9‐trans‐quinacridono)
Authors: Ruan J. Z. , Litt M. H.
Published: April 2003

The aromatic ladder polymer, poly(1,2–8,9‐trans‐quinacridono) (PQ) has been synthesized. The intermediate polymer was also characterized. Electron paramagnetic resonance (EPR) and conductivity measurements were made on PQ. PQ packs in nematic liquid crystal form. Iodine intercalates and destroys the order during doping, while raising its conductivity by five orders of magnitude.
Polymerization in submonolayers of styrene monomer adsorbed from its vapor phase
Authors: Behbahani Houshang F. , Inoue H.
Published: April 2003

The surface coverage of porous glass (PD = 500 Å) by styrene adsorbed from its vapor (0.1–6 torr) was studied in a vacuum electrobalance. The adsorption isotherm of the monomer was analyzed by the BET method, and a full monolayer coverage was found to form at a relative pressure of 0.11, weighing 6 mg per gram of glass. Polymerization in submonolayers of adsorbed styrene was initiated by thermal decomposition of predeposited BPO and found to continue until all initiator decomposed, sample cooled, or vapor removed, hence allowing a controlled film thickness. The films were extracted in THF and analyzed by computerized GPC. Molecular weights were in the range 18000–69000. These were related to the rates of polymerization by the usual statistical correlations.
Compatibility of Poly(vinyl chloride) with Polyalkyleneoxides. I. Poly(methylene oxide) and Poly(ethylene oxide)
Authors: Margaritis A. G. , Kalfoglou N. K.
Published: April 2003

The compatibility of poly(vinyl chloride) (PVC) with linear polyethers is examined over the entire composition range. This study examines blends with poly(methylene oxide) (PMO) and poly(ethylene oxide) (PEO) of medium (MMW) and high (HMW) molecular weight. The techniques used are dynamic mechanical analysis, DSC, and optical microscopy (phase contrast and polarizing). The results indicate that all polyethers show limited miscibility in the melt at high PVC contents. Proper analysis of the Tm data using the Kwei‐Frisch and Hoffman‐Weeks procedures allows the determination of the thermodynamic interaction parameter, which is found to be close to zero for all pairs of blends.
Group contribution analysis of the damping behavior of homopolymers, statistical copolymers, and interpenetrating polymer networks based on acrylic, vinyl, and styrenic mers
Authors: Chang M. C. O. , Thomas D. A. , Sperling L. H.
Published: April 2003

The integral of loss modulus versus temperature plots in the vicinity of the glass transition temperature (loss area, LA) was characterized for various homopolymers, statistical copolymers, and interpenetrating polymer networks (IPNs), based on acrylics, vinyls, and styrenic mers. The quantity LA was found to be a molecular characteristic, governed by the structure of the individual mers. The LA of both IPNs and statistical copolymers obeys an additive relation of the component polymers. A group contribution analysis for LA was developed in which each moiety contributes a specific value to LA. A table derived via this group‐contribution analysis permits the prediction of LA values. The results show that backbone motions and the moieties attached directly to the backbone contribute the most to the damping peak, and that long side chains act as diluents.
The role of colloid formation, imidization, and aggregation in the structure of BTDA‐ODA polyimide films modified with gold
Authors: Madeleine D. G. , Ward T. C. , Taylor L. T.
Published: April 2003

High‐temperature polyimide films with metallic gold surfaces can be fabricated by the incorporation of a soluble metal salt into a solution of polyamic acid. Thermal treatment of these solutions produces the polyimide, decomposes the metal salt to metallic gold, and promotes the formation and growth of the metallized surface. What appeared to be a continuous metallic surface was actually composed of large gold aggregates. It is suspected that the formation of colloidal gold during the initial thermal treatment provides precursors to the large metal aggregates. Thermal treatment has been shown to influence the size and distribution of the aggregates. The shape of the aggregates suggests that diffusion‐limited aggregation may be responsible for the unique shape of some of the gold aggregates.
Fundamental aspects of stress, deformation, and phase transitions in crystallizable polymers: Experiments with poly(ethylene terephthalate) in uniaxial stress fields
Authors: Desai Prashant , Abhiraman A. S.
Published: April 2003

Interactions between rheology and fluid→solid transformations through crystallization are demonstrated through an experimental study of crystallization of polyethylene terephthalate in uniaxial stress fields. Effect of the strength of the stress field on the kinetics of crystallization is shown to diminish greatly beyond the initiation of crystallization. Consequences of crystallization in anisotropic stress fields in the generation of mechanical properties are also described. This experimental study points clearly to the deficiencies in current theoretical formulations of kinetics of crystallization.
Structure development of fibers from liquid‐crystalline PET/60PHB copolyester
Authors: Chen G. Y. , Cuculo J. A. , Tucker P. A.
Published: April 2003

Effect of extrusion conditions, particularly temperature, on the structure development of fibers from poly(ethylene terephthalate) modified with 60 mol% p‐hydroxybenzoic acid was investigated. Light microscopy revealed that the structure of the liquid‐crystalline fiber was highly dependent on the extrusion temperature: low‐temperature‐spun fibers exhibited a structure with domains or clusters of crystallites randomly oriented, whereas the fibers spun at high temperatures had a well‐developed fibrillar texture. Anisotropy of the fibers, as evidenced by dichroism and by the variation of brightness or darkness of the fibers between crossed polars, was significantly higher for those spun at relatively high temperatures. Scanning electron microscopy revealed that the fibers spun at relatively low temperatures had poorly oriented, nonuniform morphology. Those produced at relatively high temperatures, on the other hand, consisted of well‐developed fibrils. X‐ray diffraction patterns showed that the molecular orientation increased with increasing extrusion temperature. A model for the development of fiber structure from thermotropic liquid‐crystalline polymers is proposed.
Electrical properties of MOS and MIS diodes using an electrochemically prepared poly(N‐methylpyrrole)
Authors: Tsunoda S. , Koezuka H. , Kurata T. , Yanaura S. , Ando T.
Published: April 2003

Organic semiconductor devices using electrochemically prepared poly(N‐methylpyrrole) (PNP) were characterized by capacitance‐voltage (C‐V) measurements. A device with aluminum evaporated on the PNP behaved as a MOS (metal‐oxide semiconductor) diode in vacuum. Assuming the oxide layer between the metal and the PNP to be pure Al2O3, the MOS parameters were calculated. The values obtained for depletion width W = 166 Å and acceptor density NA = 1018 cm−3 in the PNP were reasonable by comparison with the previously reported values obtained by Schottky analysis. An indium/poly(p‐phenylene)‐1,3,4‐oxadiazole (POD)/PNP diode was prepared, and C‐V measurements were carried out in air. The diode behaved like an MIS (metal‐insulator semiconductor) device, but the characteristics showed large variation with frequency. We have proposed a schematic model for this mechanism on the basis of the results obtained by dielectric measurements of POD and the temperature dependence of the MIS characteristics.
Fiber spinning from the nematic melt. V. Flow instabilities in the 75:25 copolyester of p‐hydroxybenzoic acid and 2‐hydroxy‐6‐naphthoic acid
Authors: Krigbaum W. R. , Liu C. K. , Yang D.‐K.
Published: April 2003

We have investigated the rheological properties of the Celanese copolyester with the composition 75 mol% p‐hydroxybenzoic acid and 25 mol% 2‐hydroxy‐6‐naphthoic acid (designated as 75HBA/25HNA). Three different samples having inherent viscosities 3.0, 6.0, and 9.2 dL/g were studied. A flow instability is observed at low shear stress which produces an irregularity in the fiber diameter. The surface irregularity becomes less pronounced above a minimum shear stress, indicating that the flow instability originates in the capillary. For these nematic melts, the minimum shear stress marking the onset of more regular flow is found to decrease with increasing temperature and with decreasing inherent viscosity of the copolyester. The die swell ratio of extrudates decreases with increasing shear stress. Fibers were spun from the samples having ηinh = 9.2 and 3.0 dL/g. The initial modulus and tenacity to break for 75HBA/25HNA fibers spun at sufficiently high shear stress to produce smooth filaments are significantly lower than the values we previously reported for fibers of the 58HBA/42HNA copolyester. Moreover, the optimum properties are obtained at relatively low spin‐draw ratios. The 75HBA/25HNA polyester also exhibits a yield stress which decreases with increasing temperature. This observation indicates the presence of crystallities at the test temperatures. We believe that the higher content of HBA in the present copolymer gives rise to crystallization of HBA blocks in the thread line and that defects are introduced at higher spin‐draw ratios which cause the mechanical properties to become worse.
Analysis of the thermodynamic compatibility of interpenetrating networks during their synthesis
Authors: Cuadrado T. R. , Borrajo J. , Williams R. J. J.
Published: April 2003

A thermodynamic analysis of interpenetrating polymer networks (IPNs), at any extent of reaction during their synthesis, is presented for both simultaneous and sequential procedures. A model IPN is assumed to be built up by the independent stepwise homopolymerization of two monomers: a tetrafunctional one, A4, and a trifunctional one, A3. No reaction of copolymerization or grafting is allowed between the two types of polymers. For the case of semi‐IPNs, A3 is replaced by A2, i.e., a bifunctional monomer leading to a linear polymer. The free energy of mixing is described by a Flory‐Huggins lattice model, whereas the elastic contribution is calculated by assuming affine deformation of an ideal elastic network. Results show that a sequential polymerization gives a more incompatible system (i.e., it enters the metastable region at lower conversions) than a simultaneous polymerization starting from the same monomers. In every case, a semi‐IPN is shown to be more compatible than an IPN owing to the fact that the average size of the bifunctional monomer increases less with conversion than the size of the trifunctional monomer. When a sequential polymerization begins from a swollen gel at equilibrium, any increase in the extent of reaction of the solvent monomer will lead to its segregation from the swollen gel. The critical Flory‐Huggins interaction parameter provides a simple way to ascertain the possibility of phase separation during a simultaneous polymerization.
Thermodynamics of miscible polymer blends using a concentration‐dependent χ parameter
Authors: Riedl Bernard , Prud'Homme Robert E.
Published: April 2003

The Flory equation‐of‐state theory, as expressed by Patterson and co‐workers, has been applied to two miscible polymer blends: poly(vinyl chloride)/poly(ε‐caprolactone) and poly(methyl methacrylate)/poly(vinylidene chloride). For both blends, the variation of the polymer‐polymer interaction parameter, χ, as a function of composition, is mostly small and can be accounted for by the Flory theory. However, for poly(vinyl chloride)/poly(ε‐caprolactone) blends, at high poly(ε‐caprolactone content), the large variation of χ as a function of concentration can be explained by a variation of the surface‐to‐volume ratio of the polymers in the mixture with blend composition. The variations of the surface‐to‐volume ratios determined in this study agree with those reported in the literature using small‐angle x‐ray scattering.
Effects of molecular structure and thermal annealing on gas transport in two tetramethyl bisphenol‐A polymers
Authors: Moe M. B. , Koros W. J. , Paul D. R.
Published: April 2003

The effects of molecular structure and thermal history on the gas transport properties of tetramethyl bisphenol‐A polycarbonate (TMPC) and tetramethyl bisphenol‐A polysulfone (TMPSF) are reported. The presence of the bulky methyl side groups on the aromatic rings of TMPC and TMPSF inhibits both chain packing and molecular motions in these polymers as compared with standard polycarbonate and polysulfone. The methyl substitution results in significant increases in permeability with little or no loss of selectivity, making these materials promising candidates for membrane‐based gas separations applications. Thermal annealing produces a densification of the materials, resulting in decreased permeabilities. Selectivities remained roughly the same or increased slightly upon annealing at temperatures slightly below the glass transition temperature. Thus, thermal annealing may be useful for “fine‐tuning” a membrane's properties for applications where improved selectivity is desirable, even at the expense of decreased permeability.
Molecular segregation and nucleation of poly(ethylene oxide) crystallized from the melt. III. Morphological study
Authors: Cheng Stephen Z. D. , Bu H. S. , Wunderlich Bernhard
Published: April 2003

Solvent extraction followed by DSC, optical microscopy, and transmission electron microscopy show morphological evidence of molecular segregation for binary mixtures of poly(ethylene oxide)s (PEO). Two segregation types, namely microscopic and macroscopic segregation, have been found. A special etching method for PEO has been developed, and the crystalline textures of bulk samples crystallized at different temperatures for different molecular‐mass mixtures are reported. A linkage between optical and electron microscopy is suggested. The morphology of PEO binary mixtures is crystallization‐temperature and molecular‐mass dependent.
Morphological explanation of the extraordinary fracture toughness of linear low density polyethylenes
Authors: Mirabella Francis M. , Westphal Stanley P. , Fernando Priya L. , Ford Emory A. , Williams J. G.
Published: April 2003

The fracture toughness of commercial linear low‐density polyethylenes (LLDPE) has been found to be extraordinarily high relative to commercial low‐density (LDPE) and high‐density (HDPE) polyethylenes in previously reported investigations. The present investigation shows that this extraordinary fracture toughness cannot be explained by differences in molecular structure variables, such as molecular weight, long‐chain and short‐chain branching, fractional crystallinity, and comonomer content. Instead, the presence of a second soft phase, which was extractable with a weak solvent, in a hard semicrystalline matrix was discovered by morphological investigations of LLDPE resins. This second phase arises from the extreme compositional heterogeneity of the copolymers which comprise these LLDPE resins. No evidence for a similar morphological entity was found in LDPE and HDPE resins. This finding provides persuasive evidence that this very‐low‐crystallinity second phase performs a function similar to that of the rubberlike second phase in other high impact resins and, thus, leads to the observed extraordinary fracture toughness of LLDPE resins. Evidence for the nature and existence of this second phase is given from temperature‐rising elution fractionation and scanning electron microscopy investigations.
Effect of ionizing radiation on the dynamic mechanical properties of an epoxy and a graphite fiber/epoxy composite
Authors: Wilson T. W. , Fornes R. E. , Gilbert R. D. , Memory J. D.
Published: April 2003

TGDDM/DDS epoxy and T300/NARMCO 5208 composite specimens were exposed to 0.5 MeV electrons to dose levels up to 10,000 Mrad, and the effects of radiation on the mechanical properties were characterized using dynamic mechanical analysis (DMA). In nominally cured specimens there remain unreacted epoxide groups because the epoxy system vitrifies during the cure, preventing additional reaction. DMA shows that ionizing radiation continues the reactions of epoxide groups. Also, the ultimate glass transition is shown to decrease monotonically with radiation dose. The room temperature elastic modulus of the epoxy increases slightly with radiation, but at temperatures exceeding 100°C there is a slight decrease with radiation. There is a dynamic loss phenomena associated with the composites, not seen in the epoxy, that is thought to be due to the interphase region between the fiber and the matrix.
Polymer complexes stabilized through hydrogen bonds: A semiquantitative theoretical model
Authors: Iliopoulos Ilias , Audebert Roland
Published: April 2003

Many studies have been devoted to the formation and behavior of polymer complexes. Unfortunately, the complexity of such systems do not allow a rigorous theoretical approach presently. In this paper we develop a semiquantitative theoretical model for cooperative association between macromolecules. The model is especially adapted for reversible polymer complexes stabilized through weak interactions, e.g., through hydrogen bonds. Theoretical predictions are compared with potentiometric and viscometric experimental results of poly(acrylic acid)/polybase system and a good agreement is established. The influence of parameters such as degree of neutralization of the polyacid, concentration, and molecular weight of polymers is also conveniently predicted.
The cocrystallization of polymers: Polyethylene and its copolymers
Authors: Alamo R. G. , Glaser R. H. , Mandelkern L.
Published: April 2003

In a continuation of our study of the molecular constitution requirements for the cocrystallization of chemically similar polymeric species, we have directed attention to both homopolymer‐copolymer mixtures and copolymer mixtures of polyethylene. Molecular weight and composition fractions were used exclusively. Molecular weights of the components were matched so that attention is given to the influence of chain structure. Differential scanning calorimetry and selective extraction techniques were used to assess whether cocrystallization occurs. Linear polyethylene, and random copolymers which contained up to 2 mol% of either ethyl or acetate branches, cocrystallize upon rapid crystallization from the melt. When the branching content becomes greater than about 3 mol%, cocrystallization does not occur. Copolymers containing about 1–2 mol% are found to cocrystallize with one another. However, copolymers containing higher counit contents do not cocrystallize with one another or with samples containing a smaller amount of counit. These results can be explained on the basis of the concentration of eligible sequences that are available for crystallization.
Infrared study of a thianthrenic polymer
Authors: Bertinelli F. , Bizzarri P. Costa , Casa C. Della , Fiorini M.
Published: April 2003

With the aim of finding insights into the as‐yet unclear chemical structure of thianthrenic polymers, a detailed IR analysis on a sample previously prepared by us is reported. The IR spectrum is interpreted mainly by way of two correlated reference units: the unsubstituted thianthrene and the 1,2,4,5‐tetrahalosubstituted benzene. Since a full interpretation of the spectrum of the thianthrene molecule is still lacking, we have tried a first assignment, taking o‐dihalobenzenes as component models. The spectrum of the polymer is found to correlate well with spectra of the reference moieties. Other units, taken into account to get the most reliable picture of the polymeric structure, seem to be present at appreciable concentrations. Our results lead us to propose the existence of regular, fully intramolecularly cyclized thianthrenic segments limited by defective units, mainly 1,2,4‐trithiosubstituted benzene. A narrow peak at 886 cm−1 can be interpreted as a regularity band, supporting the existence of chain segments where the repeat units are correlated by translational symmetry.
A partial phase diagram for a mixture of polystyrene with a low molecular weight styrene‐dimethylsiloxane block copolymer
Authors: Wang Baoyu , Krause Sonja
Published: April 2003

Differential scanning calorimetry (DSC) was used to examine the miscibility of polystyrene (PS), mol. wt. 105, with a phase‐separated styrene‐dimethylsiloxane (S‐DMS) diblock copolymer, Mn = 3800, 86 wt% S. Mixtures whose S content varied from 4 to 96 wt% PS were examined at a 10 K min−1 heating rate following a 200 K min−1 cooling rate from temperatures varying from 403 to 573 K. At some compositions, two glass transition temperatures, Tgs, corresponding to PS transitions were observed; at others only a single Tg was observed. When it was assumed that the 200 K min−1 cooling rate corresponded to quenching from the starting temperature, and when the heat capacity changes at the S glass transitions were used to calculate the percentage of S repeat units undergoing each glass transition, it was possible to calculate an approximate partial phase diagram for this mixture. At 96 wt% PS, there was evidence for a small amount of mixed S phase, possibly block copolymer micelles, in equilibrium with PS; from about 60 to 90 wt% PS, the S repeat units from the block copolymer appeared to be completely mixed with the PS. At lower wt% PS, unmixed block copolymer was in equilibrium with block copolymer whose S segments were mixed with the PS. The phase diagram appeared to vary only slightly with temperature.
Chemical and electrochemical doping in poly(paraphenylene vinylene) blends
Authors: Schlenoff Joseph B. , Machado Joseph M. , Glatkowski P. J. , Karasz Frank E.
Published: April 2003

Blends of poly(p‐phenylene vinylene) (PPV), with other polymers were made by film‐casting from an aqueous mixture of the water‐soluble sulfonium salt precursor to PPV and the second polymer. The rates of chemical doping, using As F5, and of electrochemical doping, using perchlorate counter ion, of the PPV component are strongly influenced by the nature of the added macromolecule. In all cases studied the blends appear to be phase separated under all conditions. The most versatile blend was with poly(ethylene oxide) (PEO), which could be heated to 225°C without degradation and which yielded the highest electrical conductivity when doped. The utility of blends was demonstrated using free‐standing PPV/PEO blend samples as rechargeable battery electrodes.
Monoclinic‐to‐orthorhombic transformation in polyethylene
Authors: Takahashi Yasuhiro , Ishida Takeshi , Furusaka Michihiro
Published: April 2003

The monoclinic‐to‐orthorhombic phase transformation induced by heat‐treatment in polyethylene was studied by x‐ray and neutron diffraction. X‐ray diffraction patterns obtained with a position‐sensitive proportional counter system showed overlaps of the several reflections of orthorhombic and monoclinic forms. Therefore, they were resolved into individual peaks by assuming the Gaussian‐Cauchy function. From the intensity distributions in reciprocal space, the geometrical relation between two forms in the transformation was clarified. Furthermore, a mechanism was proposed from the change in half‐widths. In a crystallite, the boundary between the orthorhombic and monoclinic forms, parallel to the orthorhombic (110) and monoclinic (010) planes, moves to the monoclinic side as annealing proceeds, and the transformation takes place.
Studies of self‐diffusion of poly(dimethylsiloxane) chains in PDMS model networks by pulsed field gradient NMR
Authors: Garrido Leoncio , Mark James E. , Ackerman Jerome L. , Kinsey Robert A.
Published: April 2003

We have measured the diffusion of poly(dimethylsiloxane) (PDMS) chains in PDMS model networks by using a pulsed field gradient NMR technique. The model networks have been prepared by tetrafunctional endliking of linear PDMS chains having molecular weights Mn of 3,700 and 7,400 g mol−1. The diffusants have been incorporated in the networks by immersing pieces of them in PDMS linear chains with molecular weights Mn between 3,000 and 12,000 g mol−1 and molecular weight distributions Mw/Mn between 1.1 and 1.7. Although spin‐echo attenuation results were fitted to a model which takes into account polydispersity of the diffusant, these results did not exhibit any dependency upon the molecular weight distribution. The self‐diffusion coefficients of PDMS chains in the PDMS model networks were found to be smaller than in the melt, and the exponents for the diffusion coefficient dependence on Mn in the networks were found to be about‐1.3. Free diffusion will give an exponent equal to‐1, whereas free volume contributions or behavior intermediate between free and entangled diffusion will increase the magnitude of the exponent.
Layer‐lattices in Ziegler–Natta catalysts
Authors: Zannetti R. , Marega C. , Marigo A. , Martorana A.
Published: April 2003

Some layered inorganic compounds of interest in old and new polymerization processes by Ziegler‐Natta stereospecific catalysis have been studied. The results are reported of an investigation concerning the crystallographic disorder phenomena in α‐TiCl3, VCl3, FeCl3, ball‐milled α‐MgCl2, β‐MgCl2, and in a new catalytic system produced according to some recent trends in the field. Best fits are reported of the experimental x‐ray diffraction patterns with patterns calculated for a theoretical model that accounts for structural disorder; the different fits indicate that disorder phenomena due to stacking faults are rather frequent in the examined compounds. The catalytic systems are more and more dispersed, and the maximum of dispersion in heterogeneous systems is reached for the recently proposed formulations.
A nucleation theory for the anomalous freezing point depression of solvents in swollen rubber gels
Authors: Honiball D. , Huson M. G. , McGill W. J.
Published: April 2003

It is shown that, on cooling, solvent present at the surface of swollen vulcanizates freezes before the onset of freezing in the gel solvent, causing gel solvent to diffuse to the sample surface where it adds to existing crystalline areas. At the freezing point of the gel solvent a liquid‐solid equilibrium does not exist, and a theory is postulated to account for the freezing point depression observed in swollen gels in terms of the conditions required for the formation of crystalline nuclei within the gel solvent. The theory is shown to apply to the freezing of cyclohexane and benzene in vulcanized and unvulcanized natural rubber. In line with the theory the presence of carbon black does not alter the solvent freezing point, but vacuole formation around nonreinforcing fillers leads to lower freezing point depressions.
Electroinitiated polymerization of halophenols: Electroinitiation potential‐lumo relations
Authors: Türker L. , Kisakürek D. , Şen Ş. , Toppare L. , Akbulut U.
Published: April 2003

Electroinitiated polymerizations can be carried out by direct electron transfer via constant potential electrolysis.1–3 In doing so, the anodic (Ep, a) and the cathodic (Ep, c) potentials of the monomers must be measured by cyclic voltammetry. The cathodic peak potentials of halophenols were measured on Pt0 electrode versus Ag0/Ag+ in acetonitrile.

Electroinitiated polymerization of bis(pyridine), bis(4‐chloro‐2,6‐dibromophenoxide) copper (II) complex was studied in dimethylformamide‐tetrabutylammonium fluoroborate by direct electron transfer from the cathode. Poly(phenylene oxides) obtained from the anolyte revealed that the monomer undergoes 1,2 as well as 1,4 addition reactions.

Lowest unoccupied molecular orbital energies of the monomers were calculated by Hückel molecular orbital theory. The experimental Ep, c values were correlated to theoretical LUMO energies and electron densities using a multivariable linear regression model.
Uniaxial drawing of poly(ethyleneoxide)/poly(methyl methacrylate) blends by solid‐state extrusion
Authors: Kim Bong Shik , Porter Roger S.
Published: April 2003

Ultradrawn ribbons of solution‐cast blends of poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) have been prepared by a solid‐state coextrusion in a capillary rheometer. An increase of noncrystallizable PMMA in the blends drastically decreased the drawability from a draw ratio of 36 for pure PEO to 5 for a mixture of PEO/PMMA 40/60% by weight. A low crystallinity and depression of melting temperature for PEO were observed with increasing draw. The Flory‐Huggins theory for melting temperature depression has been used to derive the binary interaction parameter for these blends.
Effect of drawing on the α relaxation of poly(vinyl alcohol)
Authors: Garrett Paul D. , Grubb David T.
Published: April 2003

The α relaxation of isotropic and drawn poly(vinyl alcohol) dried gel films was studied using dynamic mechanical analysis. The temperature of the relaxation Tα increased from 160°C in the isotropic gel to 220°C in a fiber drawn 19 ×. The relaxation, which is associated with the crystalline regions of the material, also decreased continuously in magnitude as drawing proceeded, although crystallinity increased. At draw ratios over 12 ×, the relaxation became difficult to resolve, and no relaxation was observed in fibers drawn over 19 ×. The melting points of the fibers increased with draw ratio, but not enough to account for the large change in Tα. Crystal thickness in the fiber direction also increased with draw ratio. An analogy is drawn to the case of polyethylene where crystal thickness has been found to control Tα. The absence of a resolvable α relaxation is one reason why it is difficult to draw poly(vinyl alcohol) gels to extremely high ratios.