bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of counterion distribution in polyelectrolyte solutions by the rate of reaction of two charged species
Authors: Morawetz H.
Published: April 2003

It is shown that second‐order rate constants of reactions of two charged, small molecules yield parameters characterizing the counterion distribution in solutions of polyelectrolytes. The rates constant is larger than in conventional buffers if the reagents carry charges of the same sign and smaller if they carry charges of opposite sign.
Proton magnetic resonance of some polyamides
Authors: Woodward A. E. , Glick R. E. , Sauer J. A. , Gupta R. P.
Published: April 2003

Proton magnetic resonance of a number of polyamides has been investigated in the 80–410°K. range. Line width and second moment vs. temperature plots for dry specimens of poly(hexamethylene adipamide) and poly(hexamethylene sebacamide) are found to exhibit two transition regions. Saturation with H2O or D2O lowers the temperature of the principal line‐narrowing process for the above two polymers as well as for poly(decamethylene sebacamide) and shifts part of the second‐moment transition which occurs above room temperature to lower temperatures; in both cases H2O has a more pronounced effect than D2O. Exchange of the protons, presumably on the amide groups, for deuterium leads to small decreases in line width and second moment at temperature in and below the main transition. N‐methylation of poly(decamethylene sebacamide) up to 58% causes marked shifts of the principal line‐narrowing process and NMR second moment transition to lower temperatures. The NMR data are found to be in qualitative agreement with dynamic mechanical measurements on similar samples.
Polymerization in the crystalline state. I. Acrylamide
Authors: Fadner T. A. , Morawetz H.
Published: April 2003

Crystalline acrylamide was irradiated at −78°C. with γ‐rays and the postpolymerization of the irradiated crystals was studied in the temperature range 0–60°C. The polymerization rate decays rapidly at low conversion, and the polymer yield is, for long polymerization times, linear in the logarithm of time. The activation energy for the polymerization is 25 kcal./mole. The molecular weight of the polymer depends at a given polymerization temperature on the polymerization time, but remains unchanged over a sixteenfold variation of the irradiation dose. The number of polymer chains, as deduced from the ratio of polymer yield and molecular weight, increases only slightly with conversion, probably due to chain transfer to monomer. The number of chains calculated in this way is in satisfactory agreement with the number of radicals estimated from electron spin resonance. The ESR signal changes very little during the postpolymerization. The presence of oxygen has little effect on the polymerization. Molten and shock‐cooled monomer yields about twice as much polymer as large slowly grown crystals, but the molecular weight of the product is the same, implying that crystal imperfections increase slightly the chain initiation efficiency, but are without effect on chain propagation. Propionamide is isomorphous with acrylamide and forms with it solid solutions over the entire concentration range. The polymerization of acrylamide in solid solutions containing up to 10% propionamide proceeds at a rate indistinguishable from that for pure acrylamide; at higher propionamide concentrations the rate falls off less rapidly than the concentration of the monomer. The molecular weights of polymers obtained from solid solutions approach a limiting value for long polymerization times which is determined by chain transfer to propionamide. Up to 10% propionamide concentration, the limiting polymer chain length is inversely proportional to the propionamide concentration and corresponds to a chain transfer coefficient of 0.022 at 25°C. and 0.0064 at 60°C. The high value of the chain transfer coefficient at 25°C. is ascribed to the directing influence of the crystal lattice which makes it difficult for a chain to “grow around” a site occupied by a propionamide molecule. The gradual loosening of the lattice restraints at higher temperatures explains the decrease in the chain transfer at higher temperatures. Acetamide is not isomorphous with acrylamide, but a limited amount of acetamide can be incorporated into the acrylamide lattice; the polymerization of such solid solutions exhibits, however, no chain transfer. X‐ray diffraction studies indicate that partially polymerized acrylamide contains separate monomer and polymer phases. Since the chain transfer behavior of propionamide and other evidence points to the importance of lattice control in solid‐state polymerization, it is suggested that the polymer chains grow at a monomer—polymer interface with the growing end anchored in the crystal lattice of the monomer.
Studies on polyoxypropylene glycols. Part IV. Elastic properties of derived elastomers
Authors: Conway B. E.
Published: April 2003

The stress‐strain behavior of three elastomers prepared from polyoxypropylene glycols has been examined, and the components of the elastic retractile force have been derived for one of the polymers. The data are used as a basis for interpretation of the swelling equilibrium behavior reported in the previous paper (Part III). The swelling volume ratios for the elastomers swollen in nonpolar solvents are related to the retractile forces at a given elongation in the manner expected theoretically. The degree of crosslinkage as determined by the number of elastic elements per cubic centimeter is discussed in relation to the retractile force and equilibrium swelling measurements.
A theory of the thermodynamic behavior of nonelectrolyte solutions. VI. Critical miscibility of polymer solutions
Authors: Maron Samuel H. , Nakajima Nobuyuki
Published: April 2003

Maron's theory of the thermodynamics of nonelectrolyte solutions has been applied to the condition of critical miscibility in polymer solutions on the basis of an interaction parameter μ linearly dependent on the volume fraction v2, i.e., μ=μ°+σ°v2. The results yield expressions for μc, μc°, σc°and (μc° − σc°) at the point of critical miscibility which are related to the molar volume ratio, the critical volume v, and effective volume factors. For the limit of infinite molecular weight these equations yield σc°= 1/6, (μc° − σc°) = 1/2 and μc= μc°=2/3. These results differ from the χc=1/2 predicted by the Flory‐Huggins theory on the basis of an interaction parameter χ independent of concentration.
Anhydrous lithium perchlorate as an initiator of vinyl polymerization
Authors: Hodgdon Russell B.
Published: April 2003

Anhydrous lithium perchlorate is an effective catalyst for the polymerization of certain vinyl monomers. Evidence shows that it behaves more as a cationic catalyst than a radical type, but is much milder in action than the better known representatives of this type of catalyst. Other perchlorates and lithium compounds show only a fraction or none of the activity of anhydrous lithium perchlorate in initiating vinyl polymerization.
Polyethylidene from diazoethane upon metal catalysts: Chromatographic analysis of evolved gases and mechanism of reaction
Authors: Nasini A. G. , Saini G. , Trossarelli L. , Campi E.
Published: April 2003

It has already been shown that many pure metals, as evaporated metal films, are suitable catalysts in giving polyethylidene from the decomposition of diazoethane in ethereal solution, whilst other metals (for instance Ag and Pd), although decomposing diazoethane, do not give polymer. The composition of the gases evolved during the reaction, as obtained by gas chromatographic analyses, is different in the two cases: besides nitrogen the 2‐butenes represent the main fraction of the gases evolved when polymer formation occurs; ethylene when no polymer is formed is the most important fraction of the light hydrocarbons evolved. A mechanism for the reaction of polymer formation from diazoethane is proposed, as derived from the results reported here.
Solid state polymerization of formaldehyde induced by ionizing radiation
Authors: Tsuda Yoshizo
Published: April 2003

Irradiation with gamma rays or electrons of solid formaldehyde at −196°C. induces polymerization, which proceeds explosively on warming the irradiated solid monomer. The G value for conversion was much larger than those of any other radiation polymerizations. Polyoxymethylene of very high molecular weight was obtained in bulk and in solid solution irrespectively of dose rate and irradiation time. Acrylonitrile was found also to polymerize explosively on warming the solid monomer irradiated at −196°C. It was concluded that ions or highly excited molecules formed from the irradiation at −196°C. are trapped in the solid state and that they initiate the polymerization on warming the irradiated solid monomer.
Vinyl polymerization photosensitized by uranyl ions
Authors: Mahadevan V. , Santappa M.
Published: April 2003

A systematic investigation of the kinetics of polymerization of the vinyl monomers methyl methacrylate, methyl acrylate, and acrylonitrile in aqueous solution, photosensitized by uranyl ions, was undertaken. Light of wavelengths 300–450 mμ was used for irradiation. Complex formation and ion‐pair formation was kept to the minimum. The course of the reactions was followed in terms of rates of monomer disappearance, rates of uranous ion formation, and the chain length of the polymer formed. Under controlled conditions of acidity and ionic strength, quantitative correlations between the various rates and chain length, and the variables (1) fractional light absorption, (2) uranyl ion concentration, (3) wavelength of incident radiation, (4) monomer concentration, (5) light intensity, and (6) temperature of the reaction were obtained. The influence on the reaction of uranous ion present initially in the system was studied. The quenching of the fluorescence of uranyl ions by vinyl monomers and by other standard quenchers was compared. The tentative mechanism proposed for the overall reaction is discussed in the light of these experimental results. Ratios of specific rate constants and activation energies for the various steps have been evaluated.
Analysis of intrinsic viscosity data
Authors: Kawai Tōru , Kamide Kenji
Published: April 2003

In order to interpret quantitatively intrinsic viscosity data for polymer solutions, especially for chains of poor flexibility, the partially free draining effect discussed in the theories of Kirkwood and Riseman and Debye and Bueche must be also taken into account, as well as the excluded volume effect considered in the theory of Flory and Fox. Although the Flory‐Fox theory is widely used at present for analysis of intrinsic viscosity data, it appears that in most actual cases the draining effect may also play an important part and the two effects may overlap each other to some extent. A new method has been presented in this paper, through which the separation of these tow contributions becomes possible. The exponent a in the Mark‐Houwink equation, [η] = KmM̄va, is divided into two parts: a1, related to the volume effect, and Δ, related to the draining effect. Making use of the theoretical relationship between Km and a, which was derived in the preceding paper, we can calculate the value of Δ, if the Mark‐Houwink constants have been established for a given series of polymer homologues in two solvents. In this way, we can discuss the volume effect and the draining effect separately, and interpret completely intrinsic viscosity data in terms of the parameters appearing in the Flory‐Fox and Kirkwood‐Riseman theories. Furthermore, a new method has been proposed for estimating the Mark‐Houwink constants from the measurements of intrinsic viscosity and molecular weight for a single sample. Only one sample need be used, and thus recourse to the usual more laborious methods is unnecessary. General applicability of our methods has been shown by several examples cited from published data.
Diffusion of gases and vapors through polyvinyl chloride–polyvinyl acetate copolymer films II. The effect of polymer segment mobility
Authors: Kumins C. A. , Roteman J.
Published: April 2003

The minimum free volumes involved in the diffusion of gases of various sizes through a copolymer of polyvinyl chloride–polyvinyl acetate have been calculated by use of equations developed by F. Bueche. It was found that as the gas diameter of the diffusant increased, the minimum free volume for diffusion increased exponentially. Bueche's modification of the Williams, Landel, and Ferry equation permitted use of the diffusion data to determine the number of polymer segments that cooperate in the diffusion process for each particular gas. The internal pressure of the polymer and the energy of activation for viscous flow were also calculated from the gas diffusion data. A discussion of the results is given.
Birefringence in a strained viscoelastic fluid under steady‐state rotary conditions. II
Authors: Gill Stanley J. , Dintzis Frederick R.
Published: April 2003

A rotary strain device for introducing a calculable amount of strain into a viscoelastic fluid under essentially zero flow conditions has been built and tested. The principle of the device is based upon the continuous deformation of a flexible Teflon tube which is rotated within a closely fitting, stationary, rigid metal tube that has an elliptical cross section. A polymer solution placed in such a rotating tube is subjected to an alternating strain and rotation of the bulk material. Under such conditions a steady‐state situation occurs where the material has well defined anisotropic properties. This anisotropic state is characterized by measuring both the retardation and orientation of the principle axes of the induced birefringence with a Soleil Babinet compensator. Measurements made on fluid systems at rotations of approximately 50–400 rpm yield experimental results that agree with general theoretical requirements. Mooney has analyzed the analogous situation of a microscopic rotating region. This analysis, when applied to measurements made in the rotary strain device, permits calculation of functions proportional to the storage modulus, the loss modulus, and the relaxation function of the polymer. Measurements and calculations are presented for carboxymethyl cellulose solutions in water.
The catalyst‐forming reaction between trimethylaluminum and titanium trichloride
Authors: Rodriguez L. , Gabant J.
Published: April 2003

Experimental data and a reaction scheme concerning the reaction between TiCl3 and Al(CH3)3 are presented. The reaction yielding a polymerization‐active catalyst was studied in the absence of a solvent, predominantly at 65°C. The conclusion is drawn that about half of the carbon present on the catalyst is in the form of easily exchangeable CH3 groups.
New polyelectrolytes: Synthesis and preliminary characterization
Authors: Blatz P. E.
Published: April 2003

Methacryloyl chloride was polymerized in a solvent mixture of benzene and cyclohexane. The degree of polymerization was determined for the methyl ester in acetone. Solid amino acids and hydroxy acids were added to the poly(methacryloyl chloride), and the insoluble polyelectrolytes that formed were separated and purified in selected solvents. In this manner derivatives of glycine, p‐aminobenzoic acid, sulfanilic acid, β‐alanine, and glycolic acid were prepared. The resulting polyelectrolytes were subjected to acid and base hydrolysis. The amide bonds showed considerable stability while the imide bonds were readily hydrolyzed. The results of elemental analysis, degree of hydrolysis, infrared analysis, and titration are used to arrive at a qualitative description of the structures.
Thermal degradation of polymers. I. Aspects of polytetrafluoroethylene degradation
Authors: Goldfarb I. J. , McHenry R. J. , Penski E. C.
Published: April 2003

The mechanism of the thermal degradation of polytetrafluoroethylene is investigated. It is shown that the chain transfer reaction should not be ignored and that a reasonable explanation for the observation that monomer is almost the exclusive product of vacuum thermal degradation is the rate of diffusion and volatilization of larger fragments from the polymer. Diffusion of tetrafluoroethylene and hexafluoropropylene through polytetrafluoroethylene was studied. The diffusivities are 72 and 39 × 10−10 cm.2/sec. for C2F4 and C3F6, respectively, at 24°C. An apparatus for measuring the weight and temperature of degrading polymers under vacuum is also described.
Thermally stable salts of polyvinylphthalic acid
Authors: Winslow Eugene C. , Laferriere Arthur
Published: April 2003

The heretofore unreported monomer 4‐vinylphthalic acid has been synthesized and characterized. Polymerization in aqueous solution employing a peroxydisulfate–hyposulfite redox catalyst system yielded glasslike polyvinylphthalic acid. Molecular weights of polyvinylphthalic acid appear to be in the range of 104–105. Alkaline earth polyphthalates show thermal stability to temperatures of 560°C. for periods of approximately 1 hr. Phthalocyanine crosslinks can be formed between chains of polyvinylphthalic acid, but such polymers do not show remarkable thermal stability.
Persistent polarization in poly(vinylidene fluoride). III. Depolarization and pyroelectricity of poly(vinylidene fluoride) thermoelectrets
Authors: Murayama Naohiro , Hashizume Hideyuki
Published: April 2003

Persistent polarization in poly(vinylidene fluoride) thermoelectrets prepared under high electric field has been studied by measurements of depolarization and pyroelectricity. Various polarizations are examined in detail; the polarizations related to a characteristic molecular motion near 60°C and the polarizing temperature are not responsible for the major piezoelectric effect in β‐form electrets. The piezoelectricity is attributed to a polarization appearing near the melting temperature. The persistent polarization corresponding to d31 of 2 × 10−11 coul/N is about 5 × 10−6 coul/cm2. The pyroelectricity of β‐form electrets is linearly correlated with the piezoelectricity.
Application of semiempirical melting formulas to the melting of polymer crystals
Authors: Bohlin L. , Kubát J.
Published: April 2003

This paper discusses the applicability of three melting equations to the melting temperature and its pressure dependence in polymer crystals. The equations considered are the empirical Simon equation and two semiempirical equations, the Lindemann equation and the anharmonic potential barrier equation (APB equation). It was found that although the Simon equation fits melting curves of polymeric solids well, it is merely an interpolation and extrapolation formula. There appears to be no correspondence between theoretical and experimental values of the exponent in the Simon equation. With regard to the melting temperature at atmospheric pressure, the APB and Lindemann equations perform equally well. Using the value 3.5 for the universal Grüneisen constant, it is shown that T (Lindemann) = 1.07 T (APB). On the other hand, the different physical arguments behind the two approaches lead to a very different behavior at high pressures. For the predicated initial change of melting temperature with increasing pressure a ratio close to 5:1 is obtained between the APB and the Lindemann equation. For high‐density polyethylene the Lindemann equation yields a melting temperature of 470°K when θ3 = 112°K given by Wunderlich is substituted for the Debye temperature. The observed melting temperature 405°K Corresponds to a Debye temperature of 107°K. The increase of the melting temperature with pressure for high‐density polyethylene is predicted as 31°K/kbar by the Lindemann equation as compared with 23°K/kbar found by experiment.
Comparison of head‐to‐head and head‐to‐tail polystyrenes by thermally stimulated discharge
Authors: Marchal E. , Benoit H. , Vogl O.
Published: April 2003

Thermally stimulated depolarization (TSD) experiments were carried out on several polystyrene samples. They included normal head‐to‐tail polystyrene (atactic) obtained by anionic polymerization of styrene, amorphous and substantially crystalline isotactic polystyrene, and the newly available head‐to‐head polystyrene. By TSD, six maxima of current intensity occurred at specific temperatures. Their features are compared for the various samples. Only three peaks could be identified with transitions which had been found by other techniques. Peak 5, located near Tg, is the primary relaxation. Maximum 6 could be the transition found above the Tg by torsional braid analysis and called T11 for polystyrene samples. Maximum 1 seems to correspond to what is sometimes referred to as the γ transition.
Small‐angle x‐ray scattering and crystallization kinetics of poly(ethylene terephthalate) crystallized in a liquid environment
Authors: Makarewicz P. J. , Wilkes G. L.
Published: April 2003

By small‐angle x‐ray scattering, a systematic investigation was performed of the long spacing of poly(ethylene terephthalate) (PET) crystallized in a liquid environment. The results indicated that the measured long spacings were temperature dependent and apparently relatively insensitive to liquid type under the conditions studied. The kinetic nucleation model of polymer crystallization was found to adequately explain this dependence. The differences in the long spacings between thermal and liquid‐induced crystallization were in part rationalized in terms of the suspected supercoolings involved in the respective processes. Calculation of the spherulite growth rates for liquid‐induced crystallization was made on the basis of the kinetic nucleation model and the classic theory of polymer–diluent crystallization. The results were shown to agree with inferential experimental observations of these growth rates and to elucidate the physics underlying liquid–induced crystallization. Finally, use of this growth rate theory in conjunction with a previous model for overall crystallization kinetics was shown to adequately describe and predict the diffusion‐limited kinetics observed experimentally for most liquid‐induced crystallization situations.
Model of sorption of simple molecules in polymers
Authors: Pace R. J. , Datyner A.
Published: April 2003

A model of simple molecule sorption in polymers is proposed which embraces both the glassy and rubbery regions, and incorporates the successful dual‐mode model below the glass‐transition temperature. Hole filling is shown to be an important sorption mechanism both above and below Tg, although saturation effects do not occur in the rubbery polymer. The model interprets the “dual‐mode” Langmuir and Henry's law parameters at the molecular level, and a simple statistical mechanical analysis allows estimation of the parameter values, as well as specifying certain interrelationships between the parameters. Applications of the model to gas solubility data in five polymers are considered [polyethylene (PE), poly(ethylene terephthalate) (PET), polystyrene (PS), polymethacrylate (PMA), poly(vinyl acetate) (PVAc)] and semiquantitative agreement is obtained for PE, PET, and to a lesser extent, PS. For PMA and PVAc, the agreement is qualitative only.
Analysis of the products of copolymerization with chain branching in the pregelation stage
Authors: Mrkvičková Libuše , Kratochvíl Pavel
Published: April 2003

The copolymerization of methyl methacrylate with small amounts (0.25‐1 mol %) of bis (4‐methacryloxybenzilidene)‐1,2‐diaminoethane in the pregelation stage was investigated. The mole fractions in the copolymers of the divinyl monomer, of the reacted vinyl groups of divinyl monomer, and of the totally reacted divinyl monomer units forming intermolecular crosslinks were determined experimentally and some other parameters were calculated from these quantities. The amount of intramolecular crosslinks, forming closed rings, has been shown to predominate over the amount of intermolecular crosslinks. The comparison of the experimental data with values calculated from Wesslau's theory, based on the classical concepts of copolymerization, reveals differences increasing up to an order of magnitude with rising content of the divinyl monomer. A major reason for this divergence appears to be the intramolecular crosslinking.
Calculation of electronic band structures for some rigid benzobisoxazole and benzobisthiazole polymers
Authors: Bhaumik D. , Mark J. E.
Published: April 2003

Quantum‐mechanical methods were employed to calculate electronic band structures for the polybenzobisoxazole (PBO) and polybenzobisthiazole (PBT) chains originally synthesized and much studied because of their utility as high‐performance fibers and films. For cis‐PBO, trans‐PBO, and trans‐PBT chains in their coplanar conformations, the band gaps in the axial direction were found to be 1.72, 1.62, and 1.73 eV, respectively. Since trans‐PBT is nonplanar, calculations on it were also carried out as a function of the rotation angle ϕ about the C—C bond joining the two +ing systems in the repeat unit. The band gap was found to increase markedly with increase in nonpla‐narity, as would be expected from the decrease in charge delocalization. The calculations suggest the most likely value of ϕ to be ca. 30°, in good agreement with the experimental value 23° obtained by x‐ray analysis of a crystalline trans‐PBT model compound. At this value of ϕ, the calculated value of the band gap is.1.98 eV. All of these values are very close to the corresponding values of 1.4‐1.9 eV reported for trans‐polyacetylene, which should encourage further theoretical and experimental investigations of the electronic properties of these polymers.
Properties of semidilute polymer solutions: Investigation of an optically labeled three‐component system
Authors: Cotts David B.
Published: April 2003

A three‐component system containing a polymer (2), a good solvent (1) for that polymer, and a second polymer (3) that is compatible with component (2) and isorefractive with the solvent (1) has been studied by static and dynamic light‐scattering methods. In concentrated toluene (1) solutions of poly(vinyl methyl ether) (3), where appreciable chain overlap occurs and excluded‐volume effects are reduced, polystyrene (2) may be studied in the dilute‐solution limit. Consequently, these light‐scattering measurements provide an explicit measure of both thermodynamic and hydrodynamic changes that occur as the total polymer concentration is increased from dilute to concentrated solution. Precise numerical coefficients, correct scaling exponents, the radius of gyration, and the effective hydrodynamic radius can be measured directly along with the observation of long‐wave single‐chain reptation motions and short‐range cooperative motions in semidilute and concentrated solutions.
Fourier‐transform infrared studies of the thermal degradation of isotopically labeled polyacrylonitriles
Authors: Rafalko Joseph J.
Published: April 2003

Poly(d3‐acrylonitrile), poly(1‐13C‐acrylonitrile), poly(15N‐acrylonitrile), and 18O2 have been used to assign the infrared spectra of the thermal degradation products of polyacrylonitrile. Isotopic data and elemental analyses show that the degradation products can be made free of oxygen. The infrared data suggest that the reaction proceeds sequentially from imines to fused pyridine‐dihydropyridine moieties.
Linear polymers in nonhomogeneous flow fields. I. Translational diffusion coefficient
Authors: Brunn P. O. , Grisafi S.
Published: April 2003

The translational diffusion coefficient D, needed in treatments of flow‐induced polymer migration phenomena, is studied. Explicit results are reported for bead–spring model macromolecules with two, three, and four beads, respectively. If the number of beads is large, an integral formulation is used. The results obtained show that D depends upon the hydrodynamic interaction parameters h* and h*N1/2. Nondraining behavior of D is predicted irrespective of h if h* is close to 0.2357. Approximations for D are obtained and the error involved is estimated.
Heat capacities of liquids linear aliphatic polyoxides
Authors: Suzuki Hidematsu , Wunderlich Bernhard
Published: April 2003

Heat capacities at constant pressure of liquid polyoxymethylene (430‐540 K) and polyoxyethylene (330‐430 K) have been measured by scanning calorimetry. These new data are discussed together with the heat capacity of polyethylene and other linear, aliphatic polyoxides to arrive at a wide‐range addition scheme for heat capacities. Values of absolute entropy, enthalpy, and Gibbs free energy are estimated. The new data are offered as “Recommended Data 1984” in our ATHAS Data Bank.
Surface modification of contact‐lens materials by silanization: An FTIR‐ATR study
Authors: Khoo C. G. L. , Lando J. B. , Ishida H.
Published: April 2003

The adsorption, desorption, and orientation characteristics of two long‐chain chlorosilane compounds, octadecyltrichlorosilane and 1‐undecylene‐dimethylchlorosilane, onto poly(methyl methacrylate) (PMMA) and poly(2‐hydroxyl‐ethyl methacrylate) (PHEMA) are studied using Fourier‐transform infrared attenuated total reflection (FTIR‐ATR) spectroscopy. Quantitative monitoring of the amount of silane adsorbed is also attempted. It is believed that the surface modification reaction has been successfully confined to monolayer coverages and that sufficient detection sensitivity has been achieved to observe the reaction at these low levels on both PMMA and PHEMA. Also, ATR polarization studies indicate that on both substrates, a definite preference for orientation exists such that the long molecular axis is perpendicular to the substrate surface. The silanes are observed to be only physisorbed onto the PMMA surface under the anhydrous conditions applied during adsorption, whereas a chemical reaction is observed on the PHEMA surface.
Chemiluminescence from oxidation of polypropylene: Some comments on a kinetic approach
Authors: Billingham Norman C. , George Graeme A.
Published: April 2003

We present a detailed criticism of the kinetic approach to the analysis of data obtained from measurements of the very weak chemiluminescence accompanying the oxidation of polypropylene. It is shown that a kinetic model proposed by other workers is based upon invalid assumptions, leads to kinetic parameters which are not sensible, and requires measurement of the properties which it claims to predict.
Ion transport and states of water in charged poly(allylamine) membranes
Authors: Yonetake Koichiro , Seo Toshihiro , Iijima Toshiro
Published: April 2003

Cationically charged poly(allylamine) (PAA) membranes having various water contents [0.49 < H < 0.63 (g H2O/g wet membrane)] were prepared. Sorption and permeation of simple salts (sodium chloride and sodium tetraphenylborate) were investigated, taking into account the state of the water in these membranes. The weight ratios of freezable water and free water to total water (Wfz/Wt, and Wf/Wt) in the membranes were estimated by means of DSC and pulsed 1H‐NMR measurements, respectively. Partition coefficients K for total water were converted into those in freezable and free water, Kfz and Kf, using Wfz/Wt and Wf/Wt. The permeability of both salts in the membranes could be interpreted satisfactorily by an equation derived from the Teorell‐Meyer‐Sievers theory using values of Kf. The free water is mainly involved in the permeation of simple salts through PAA membranes while bound water hardly takes part.
The effects of physical aging in polycarbonate
Authors: Hill A. J. , Heater K. J. , Agrawal C. M.
Published: April 2003

The effects of physical aging below the glass transition temperature on selected properties of polycarbonate have been studied. Changes in tensile yield strength, post yield stress drop, and fracture toughness as a result of annealing at 120°C for 240 h have been measured and are related to changes in free volume as measured by positron annihilation lifetime spectroscopy. The free volume concentration remains constant during the aging heat treatment at 120°C but decreases after cooling due to aging. The relationship between free volume changes and physical property changes is discussed in terms of molecular conformations and fracture mode. The effect of aging on fracture morphology is presented to aid interpretations of fracture mode.
Electrical conductivity of cationic polyelectrolytes in aqueous solution
Authors: Ríos Hernán E. , Sepúlveda Luis N. , Gamboa Consuelo I.
Published: April 2003

Four different fluoride, chloride, bromide, and nitrate cationic polyelectrolytes were prepared. Their electrolytic conductivity in aqueous dilute solution was investigated. The results show a remarkable increase, with dilution being practically constant down to limiting concentration. The limiting equivalent conductivity Λ° follows the order
$\[ {\rm F}^ - \gg {\rm Cl}^ - > {\rm Br}^ - \approx {\rm NO}_3^ - \]$
The distances between neighboring charges calculated from experimental data are in good agreement with those calculated geometrically according to Manning's definition. The results are mainly dependent on the assumption that Br− and NO3− interact in a similar manner with the cationic charges on the polyion. This phenomenon also has been observed in cationic micelles.
Oxygen and water‐vapor diffusion through biaxially oriented poly(ethylene terephthalate)
Authors: Orchard G. A. J. , Spiby P. , Ward I. M.
Published: April 2003

The gas barrier properties of a wide range of biaxially oriented polyethylene terephthalate films have been investigated. The permeability and diffusion coefficients for oxygen and water vapor transmissions were determined for films prepared by both simultaneous and sequential biaxial stretching. The effect of annealing was also studied and a comparison made with previous results for uniaxially oriented films. It was found that the permeability correlated well with the density of the sample, but that the dependence on the gauche/trans conformer ratio shown for uniaxial material was not so clear. A good empirical correlation was also obtained between permeability and a proposed measure of molecular orientation obtained from refractive index measurements. A more detailed interpretation, based on infrared measurements of orientation, showed that there is a systematic reduction in permeability as the planes of the terephthalate residues become parallel to the film surface.
Gas transport and diffusive resistance in highly oriented high‐density polyethylene
Authors: Chau C. C. , Raspor O. C.
Published: April 2003

High density polyethylene was biaxially oriented by high‐pressure forging and subsequently low‐pressure thermal forming. The permeability of O2, CO2, and CH4 was reduced slightly by biaxial orientation, the diffusivity of the gases was found to increase with the degree of orientation. The solubility decreased markedly with orientation. Density measurements indicated that crystallinity increases with the extent of biaxial deformation. Based on the concept of particle flow in viscous media, the variation of gas diffusivity with orientation is viewed as a frictional resistance effect. The diffusivity is inversely proportional to a phenomenological friction coefficient; which can be related to orientation by a shape factor s. The diffusivity for the oriented state, D, is then related to that of the nonoriented state, D0, as D = D0/(1 + sϕ). The variation of diffusivity selectivity with orientation is also formulated based on this consideration. Results on both biaxially and uniaxially oriented HDPE are examined in light of this model.
Dielectric and conductivity relaxations in poly(hema) and of water in its hydrogel
Authors: Pathmanathan K. , Johari G. P.
Published: April 2003

The dielectric permittivity ε′ and loss ε″ of anhydrous poly(2‐hydroxyethyl methacrylate) and its 38.6 w/w% hydrogel have been measured in the frequency range from 12 Hz to 200 kHz and the temperature range from 77 to 273 K. The former has a sub‐Tg relaxation with a half‐width of 4.5 decades for the loss spectra, whose strength increases with temperature, and an activation energy of 62.5 kJ/mol. The dielectric relaxation time of the α process of supercooled water in the hydrogel is 53 s at its calorimetric Tg of 135 K. The half‐width of the relaxation spectrum is 2.85 decades and, in the narrow temperature range, its apparent activation energy is 60.8 kJ/mol. Heating of the hydrogel causes crystallization of water which begins at about 207 K and becomes readily detectable as a second dielectric loss peak at about 230 K. For each temperature between 207 and 267 K, supercooled water in the hydrogel coexists with its crystallized form, with the amount of the crystallized solid increasing with increasing temperature. These results are discussed in terms of “bound” and “free” states of water in the hydrogel.
Bubble nucleation in polymeric liquids. I. Bubble nucleation in concentrated polymer solutions
Authors: Han James H. , Dae Han Chang
Published: April 2003

Laser light scattering, with the aid of Mie's scattering theory, was used to investigate bubble nucleation in concentrated polymer solutions. Solutions with 40, 50 and 60 wt % polystyrene in toluene were used. A test solution in a high‐pressure optical cell made of strain‐free quartz was heated to a predetermined temperature under pressure. Upon release of the pressure in the cell, both scattered and transmitted light fluxes were measured with photomultipliers, and the variation of system pressure with time was measured using a piezoelectric pressure transducer. The measurement of the light scattering flux and control of the experiment were performed by means of a microcomputer with a general‐purpose data acquisition interface. Data reduction was done using the same microcomputer. The critical bubble size was determined by obtaining a one‐to‐one correspondence between the extrema of the experimental and theoretical scattering curves. While the Mie scattering theory is for monodisperse particles, the experimental scattering curves indicated that the bubbles had a distribution of sizes. Therefore, the log‐normal distribution function was used to represent the size distribution; and theoretical scattering curves were computed by varying the breadth parameter in the log‐normal distribution function, until we had a one‐to‐one correspondence between the extrema of the experimental and theoretical scattering curves. In this way, we were able to determine (a) the size distribution of bubbles in the optical cell, (b) the critical bubble size, (c) the total number of bubbles nucleated, and (d) the critical pressure for bubble nucleation, as functions of temperature, the initial equilibrium pressure in the optical cell, and the concentration of the polymer solution.
Graft interpenetrating polymer networks of polyurethane and epoxy. II. Toughening mechanism
Authors: Hsieh K. H. , Han J. L.
Published: April 2003

Graft interpenetrating polymer networks (graft‐IPNs) of polyurethane (PU) and the diglycidyl ether of bisphenol A (epoxy) were prepared by first grafting excess PU prepolymer to the epoxy and then simultaneously polymerizing the PU prepolymer and epoxy. The fracture properties, at high shear rate (e.g., impact) and low shear rate (e.g., pseudostatic tensile fracture energy measurement) of these graft‐IPNs exhibit opposite behavior. Although dispersed rubber particles can enhance the Izod impact strength, toughening of the matrix of graft‐IPNs was found to be the main contribution. In contrast, it was found that a heterogeneous morphology with suitably dispersed rubber domains of appropriate size as well as the toughness of the matrix are requirements for effectively increasing the fracture energy at low shear rate. A reinitiating crack in the plastic matrix is proposed as the main toughening mechanism and can be invoked to interpret the fracture behavior at high and low shear rates of the graft‐IPNs.
Diffusion after chain fragmentation in the glassy state: A SANS study
Authors: Meurer E. , Kuhn K. J. , Hellmann G. P. , Rennie A. R.
Published: April 2003

A new method to measure the extremely slow chain diffusion in polymer systems at and below the glass transition temperature is proposed. It requires polymers that can be fragmented in a well‐defined manner in the glassy state. The idea is first to split all chains, while their conformations are frozen in, and then to measure at some higher temperature the diffusion of the chain fragments by small‐angle neutron scattering. The structure factor changes in the course of the fragment diffusion from that of the initial long chains to that of the uncorrelated fragments. Preliminary results from experiments on blends of thermosensitive copolycarbonates and tetramethylpolycarbonate are presented. They demonstrate the viability of the technique.
Mass diffusion of camphorquinone in poly(methyl methacrylate) hosts with different molecular weights
Authors: Xia J. L. , Wang C. H.
Published: April 2003

Diffusion coefficients of camphorquinone (CQ) and its photoproduct (CQP) in two poly(methyl metbacrylate) (PMMA) samples with different molecular weights are measured as a function of temperature. Above the glass transition, the temperature dependence is not Arrhenius and can be described by the Williams‐Landel‐Ferry equation. It is also shown that the difference in the temperature dependence of the diffusion coefficients of CQ in the two PMMA samples is attributable to the difference in glass transition temperatures.
A free‐volume‐based approach to modeling thermoset cure behavior
Authors: Sanford W. M. , McCullough R. L.
Published: April 2003

The free‐volume theory for the temperature dependence of transport properties of glass‐forming polymers is extended to obtain their relationship to the extent of cure. This treatment centers on the unifying role of molecular mobility and yields a model which connects extent of reaction, viscosity, diffusivity, ionic conductivity and dipole relaxation time. The temporal dependence of these properties is expressed by coupling the extended free‐volume model with a relationship for the rate of cure, which included diffusional limitations. Analyses based on this model are applied to the observed behavior of a model epoxy‐amine resin system. The intrinsic kinetics of this model system are shown to be first order. It is shown that diffusional limitations strongly affected the progress of the reaction in the final stages of cure. The diffusion‐modified rate expression predictions agree with extent of reaction versus time data over the range of experimental temperatures. The temporal dependence of viscous behavior of the curing resin is measured. The extended free‐volume model accurately describes the evolution of resin viscosity during cure. The dielectric behavior is similarly characterized and is in close agreement with the predictions of the general free‐volume expression. The results of this study indicate that the free‐volume theory modified to account for molecular weight effects allows prediction of resin properties with a two‐parameter model. The results show that a power‐law relationship exists between viscosity and ionic conductivity. This result suggests that electrical properties may be used for on‐line measurement of resin viscosity during cure.
Dynamic x‐ray diffraction studies of liquid‐crystalline polyesters
Authors: Ober C. K. , Delvin A. , Bluhm T. L.
Published: April 2003

Mesophase transitions in liquid‐crystalline (LC) polyesters were studied by dynamic x‐ray diffraction using a synchrotron radiation source. Powder and fiber samples were examined by continuous heating from 50°C to 270°C in a hot stage. The polymer systems consisted of two types of thermotropic polyesters with mesogenic cores composed of combinations of substituted terephthalate, oxybenzoate and hydroquinone units combined with aliphatic spacers placed in the main chain. One of these samples was a chemically homogeneous LC polyester (HTH12) while the other LC polyester possessed chemical heterogeneity (BP6). BP6 could also be processed to form fibers which showed thermal transition behavior by x‐ray diffraction and no detectable melting or clearing transition by thermal measurements. LC textures were observed using polarized light microscopy. Results of the dynamic x‐ray diffraction studies of these two LC polymers are described.
Acoustic emission during crystallization of polymers
Authors: Galeski A. , Piorkowska E. , Koenczoel L. , Baer E.
Published: April 2003

Ultrasonic emission was found to accompany spherulitic crystallization of polymers from the melt. The source of acoustic waves was identified as an abrupt negative pressure release in regions of melt occluded by spherulites (weak spots) in the course of crystallization. The buildup of a negative pressure in occluded areas is a result of a density change during crystallization. When the level of stress approaches the limit related to melt cohesion, cavitation occurs, the stress is released, and acoustic wave is emitted. On the basis of a statistical approach to the description of spherulitic structure formation, it was predicted that most acoustic events should occur at a high degree of conversion—close to the end of crystallization. The ultrasonic emission was found during isothermal crystallization of isotactic polypropylene and poly(methylene oxide). In the case of Nylon 6, acoustic emission was attributed to environmental stress cracking and degradation. No acoustic events were recorded during crystallization of high‐density polyethylene and during similar thermal treatment of a series of noncrystallizable polymers. Addition of a nucleating agent to crystallizable polymers drastically reduces the acoustic emission during crystallization, which indicates that the spherulite size is one of the most important parameters. Depending on the size and geometry of weak spots, melt properties, and mechanical properties of spherulites, the stress in weak spots is either released by cavitation or remains frozen in the material. It was found that the time distribution of acoustic emission is located between the time distributions of the formation of weak spots and the formation of quadruple boundary points between spherulites.
Dynamic bulk modulus of various elastomers
Authors: Burns J. , Dubbelday P. S. , Ting R. Y.
Published: April 2003

The dynamic bulk modulus of elasticity has been measured for 14 different rubbery elastomers: three natural rubbers, five neoprenes, three polyurethanes, and one each of butyl, nitrile, and butadiene types. The measurements ranged in temperature from −10 to +40°C, at frequencies from 5 to 3000 Hz, but mostly in the range 100–1000 Hz, at 2.5 MPa pressure. Values of the real (storage) part of the modulus fell within 35% of the mean value of 2.9 GPa for all elastomers, whereas loss moduli were a few percent of the storage moduli. Master curves were obtained for two neoprenes, a polyurethane, and a butyl rubber. These were fitted by hyperbolic functions with four adjustable parameters. Effects of room‐temperature aging in artificial sea water were also studied. Aging versus time profiles fell into two distinct forms. Natural rubbers were least stable, neoprenes were intermediate, and urethanes proved most stable in bulk modulus.
Formation of ringed spherulites in polyethylenes
Authors: Chiu G. , Alamo R. G. , Mandelkern L.
Published: April 2003

The effects of molecular weight, molecular weight distribution, crystallization temperature, quenching medium, and sample preparation on the formation of ringed spherulites in linear polyethylenes were studied by polarized light microscopy and small‐angle light scattering. When the samples were crystallized at a predetermined temperature, ringed spherulites were formed over a narrow range of temperature and molecular weight with both fractionated and unfractionated polymer samples. Quenching the samples in air at room temperature considerably extended the range of molecular weights for the formation of ringed spherulites. Minor modification of an airquench method further extended the range and yielded better‐defined structures. The results are interpreted in terms of the anisotropy of the melt, the thermal conductivity of the quenching medium, and the shear stress applied during the crystallization process. That highly specific conditions are necessary for spherulite formation, of both the conventional and ringed type, is a major conclusion of this study.