bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fourier‐transform infrared studies of polymer blends. III. Poly(β‐propiolactone)‐poly(vinyl chloride) system
Authors: Coleman M. M. , Varnell D. F. 
Published: April 2003

AbstractFourier‐transform infrared (FTIR) studies of the poly(β‐propiolactone) (PPL)‐poly(vinyl chloride) (PVC) blend system are presented. PPL‐PVC blends are observed to be incompatible in the molten (80°C) and solid (25°C) states, over the entire range of compositions. This is in marked contrast to our previous results of the poly(ϵ‐caprolactone)‐PVC blend system which was shown to be compatible in the amorphous state. The results of both studies are compared and discussed with particular reference to the detection of intermolecular interactions by FTIR and correlation with compatibility in polyester‐PVC blends. The role of the chemical interactions in the compatibilization of polymer blends is discussed in terms of thermodynamic considerations. Finally, it is well known that changes in refractive index of polymer blend compositions can cause frequency shifts of infrared bands, which are particularly relevant to the interpretation of residual peaks obtained by difference spectroscopy. The FTIR results of the PPL‐PVC blends are germane to this subject and are discussed.
Rigid backbone polymers. XI. Solution phase‐viscosity relationship
Authors: Aharoni Shaul M. 
Published: April 2003

AbstractUsing combined results of isothermal viscosity measurements and cross‐polarized light microscopy on four polyisocyanate/solvent systems, the following were demonstrated: (a) an anisotropic phase appears, associated with a shoulder in the viscosity curve, at a concentration v lower than the peak viscosity at v; (b) the inversion from anisotropic inclusions in an isotropic matrix to isotropic inclusions in an anisotropic matrix, occurs at concentrations v > v and (c) the attainment of a single phase, microscopically anisotropic, occurs at v > v; where the viscosity is decreasing but has not yet reached its minimum. When the experiments were repeated with changes in temperature, the following were observed: (a) within each single phase the viscosity drops with increased temperature; (b) in the biphasic range, the total viscosity η0 remains about constant in the concentration range ≤ and increases with temperature in the range v > v; (c) in the interval v > v of the biphasic range, at constant temperature an increase in concentration decreases η0, and at constant concentration, a decrease in temperature lowers η0. Qualitative explanations of the observations are proposed.
SAXS analysis of a linear polyester and a linear polyether urethane—interfacial thickness determination
Authors: Ophir Zohar , Wilkes Garth L. 
Published: April 2003

AbstractA small‐angle x‐ray scattering (SAXS) investigation of two linear segmented polyurethanes was carried out to learn about the respective domain structure (morphology). Both urethanes had a hard segment of methylene‐bis(4)phenyl isocyanate (MDI) and butanediol. These two components comprised 28% by weight of each system. The soft segments differed in that one was a polyether (tetramethylene oxide, molecular weight 1000), while the other was a polyester (polytetramethylene adipate, molecular weight 1000). Both of these segmented urethanes were stored at room temperature for over 6 months prior to investigation. Using an automated Kratky camera, SAXS scans were made. By detailed analysis (using the computer program of Vonk) the average interfacial thickness E of the domains was determined by two approaches. The value of E for the polyester was 10–12 Å, while it was 5–7 Å for the polyether. Within the limits of the assumptions used for analysis, these data directly support the conjecture that polyether urethanes generally lead to better phase separation. Other aspects of the analysis provided further information on the morphological structure. Some cautionary comments are provided on the use of quantitative SAXS data obtained from these or similar systems.
Kinetics and equilibria of sulfur dioxide sorption in kapton polyimide
Authors: Koros W. J. , Patton C. J. , Felder R. M. , Fincher S. J. 
Published: April 2003

AbstractThe kinetics and equilibria of SO2 sorption in Kapton polyimide film have been measured at 25°C for pressures up to 58 cm Hg using a quartz spring balance. The observed equilibria are described well by the dual‐mode model for sorption of penetrants in glassy polymers. Observed hysteresis in sorption‐desorption cycling indicates that the diffusivity of SO2 increases markedly with increasing local penetrant concentration in the polymer. The concentration dependence of the effective average diffusion coefficient is described well by an expression from dual‐mode theory. The Langmuir component of the sorption population has an extremely low mobility compared to that of the Henry's law component; in fact, the so‐called “total immobilization” limiting case, which assigns a zero diffusion coefficient to this component, appears to be satisfactory under the conditions studied. These results, coupled with published results for other penetrants, suggest that the degree of immobilization of the Langmuir population depends to a great extent on the condensability and/or the molecular size of the penetrant. Predictions of the SO2 diffusion time lag and permeability in Kapton as functions of the upstream SO2 pressure are presented and discussed in terms of the dual‐mode theory.
Sequence distribution in ethylene‐propylene copolymers. II. The 13C NMR spectra, multad populations, and kinetic parameters
Authors: Smith Wendell V. 
Published: April 2003

AbstractMonad, dyad, and triad populations have been derived from the 13C NMR spectra of eight ethylene‐propylene copolymers. Using these values, Kinetic parameters of the polymerization have been calculated, including conditional probabilities, and reactivity ratios. The fraction of propylene entering in an inverted order has been found to be about 20%. The copolymerization is dominated by the relatively large reactivity of ethylene. There is an alternating tendency for the two monomers which is evident both in the normal addition of propylene and the inverted addition. Penultimate effects do not play a significant role.
Effect of molecular weight on the diffusion coefficient of carbon dioxide in polystyrene
Authors: Toi Keio , Ohori Yuko , Maeda Yasushi , Tokuda Taneki 
Published: April 2003

AbstractThe permeability and time lag at pressures below 1 atm were measured for carbon dioxide in five polystyrene samples with different molecular weights at 25 to 40°C. The apparent permeability coefficient decreases with increasing carbon dioxide pressure and also decreases with increasing molecular weight of polystyrene, whereas the apparent diffusion coefficient calculated from time lag increases with pressure and is independent of molecular weight. Parameters for the partial‐immobilization model were determined from the apparent diffusion and permeation coefficients by using a nonlinear least‐squares optimization program without using sorption data. The results suggest that the void‐saturation constant C′H decreases as the molecular weight of the polymer increases or as the chain‐end free volume decreases. The significance of these observation and their interpretation is discussed in terms of free‐volume theory for glassy polymers.
Comparison of theory and experiment for diffusion in dilute polymer solutions
Authors: Vrentas J. S. , Liu H. T. , Duda J. L. 
Published: April 2003

AbstractResults from a number of theories for the concentration dependence of the mutual diffusion coefficient in dilute polymer solutions are examined, and clarifications are made as to what forms of the equations for these theories should be used in comparisons with experimental diffusivity data. An evaluation of the available theories for the concentration dependence of the diffusivity under theta conditions is carried out using experimental diffusivity data taken using sharp fractions of polystyrene. It is concluded that the Pyun—Fixman theory appears to provide the most promising method for estimating the concentration dependence of the mutual diffusion coefficient in dilute polymer solutions at the present time.
Cold crystallization of polytetrafluoroethylene by γ irradiation
Authors: Takenaga Mitsuru , Yamagata Kyozo 
Published: April 2003

AbstractChanges in density and in the corresponding degree of crystallinity with radiation dose are studied experimentally for γ‐irradiated polytetrafluoroethylene (PTFE) in the dose range from 1 X 103 to 1 X 109 R. The relation between the amorphous fraction and the radiation dose is derived from a quantitative analysis of cold crystallization by scission of polymer backbone chains. The characteristic radiation dose, at which one break occurs on the average per initial molecule, is estimated as about 3 X 104 R on the basis of a derived kinetic equation. The theoretical relation is modified by considering microvoids produced in the irradiated samples. The radii of microvoids in the form of spheres are evaluated as about 0.2 nm, and are also related to cage spheres relevant to the chain scission process. Good agreement between the modified theoretical relation and experimental data is attained over the entire range of radiation dose.
Dilute solution properties of a polybenzimidazole
Authors: Kojima Takakazu , Yokota Rikio , Kochi Masakatsu , Kambe Hirotaro 
Published: April 2003

AbstractLight scattering and viscometric studies have been carried out on dilute solutions of a polybenzimidazole in N,N‐dimethylacetamide. The data, which span the molecular weight range 2.9 ≦ 10−4Mw ≦ 23.3, and the temperature range 290 ≦ T/K ≦343, yield the dependence of the mean‐square radius of gyration 〈s2〉LS, the second virial coefficient A2, and the intrinsic viscosity [η] on molecular weight Mw and temperature. The unperturbed mean‐square radius 〈s〉LS was calculated using experimental values of 〈s2〉LS and A2. It was found that excluded volume effects on 〈s2〉LS are very small. The unperturbed hydrodynamic chain dimension 〈s〉η was estimated by considering draining effects. A small value of the draining parameter was obtained. Analysis of the temperature dependence of A2 and [eta;] leads to the conclusion that this system approaches a lower theta temperature with increasing temperature. The steric factor σ = 〈s〉/〈s〉f, based on the value of 〈s〉f calculated for the polymer chain with free rotation, is nearly unity. Most of these properties can be interpreted in terms of long rotational units within the main chain.
Dynamics of noncrystalline polyethylene
Authors: Swaminathan K. , Tewari S. P. 
Published: April 2003

AbstractAn anisotropic dispersive continuum model for the collective modes of polyethylene of any degree of crystallinity is suggested. The model successfully explains the experimental results for specific heat of polyethylene of 100%, 84.1%, 74.5%, 45.9%, and 0% crystallinity in the temperature range 2.5–60 K, where the specific heat of amorphous polyethylene is markedly different from that of crystalline polyethylene. The variation of specific heat with degree of crystallinity can be obtained by varying only one parameter θ1 (characterizing the low energy cubic modes), keeping the other two parameters (characterizing the transverse and longitudinal chain modes) constant. Thus, in going from the crystalline to the amorphous state, it is essentially the interchain binding which is affected, the chain modes being left undisturbed. Using the calculated values of specific heat for varying degrees of crystallinity, the variation of θ1 with the crystallinity is reported. Observed high‐temperature specific heats for crystalline and amorphous polyethylene up to 300 K are also explained using additional optical modes. The anisotropic Mössbauer elastic scattering fraction (MESF) for polyethylene of different degrees of crystallinity in the temperature range 0–425 K is obtained. For a given degree of crystallinity there is marked anisotropy in MESF which increases with increase in temperature. For a given direction, longitudinal or transverse, there is a large difference between the MESF of 0% and 100% crystalline polyethylene, which also increases with the increase in temperature. It is quite possible that the MESF experiment may prove to be more sensitive than the usual method for the determination of degree of crystallinity.
High‐conversion emulsion polymerization in a continuous reactor: Predictions using smith–ewart kinetics
Authors: Friedman Emil M. 
Published: April 2003

AbstractSmith–Ewart Case‐2 kinetics are applied to a continuous stirred tank reactor operating at steady state in the high and middle range of conversion. Above the conversion CD at which the monomer droplets disappear in a batch reaction, the predictions are surprising. The particle size is predicted to be inversely proportional to the effective soap concentration S and independent of mean residence time θ below CD it is predicted to be proportional to the one‐third power of θ and independent of S. Above CD the particle concentration should be proportional to the cube of S and independent of θ; below this it should be as predicted by previous workers. The expressions for conversion are also different above CD. A new, more instructive, derivation is used. Simple analytic expressions are given for commonly used breadth parameters of the particle size distribution. It is shown that when conversion is low, an approximation made by previous workers is invalid, in that the growth rate can no longer be considered continuous.
Application of the porous‐sphere hydrodynamic model to dilute polymer solutions
Authors: McDonnell Milton E. , Jamieson Alexander M. 
Published: April 2003

AbstractThe porous‐sphere model of Debye–Brinkman–Bueche is applied to predict the limiting frictional coefficient f0 and intrinsic viscosity [η] of polystyrene fractions in tetrahydrofuran and random protein coils in 6M guanidine hydrochloride. Following the formulation of Wiegel and Mijnlieff, the molecular permeability is modeled to increase exponentially as the square of the distance from the center of the molecule. A method is developed to obtain this permeability from the translational diffusion coefficient. The experimental values of f0 and [η] are in satisfactory agreement with the calculated values. Also, this analysis predicts values of the Mandelkern–Flory–Scheraga parameter for flexible coils which are significantly smaller than the minimum values permitted by the Kirkwood–Riseman theory. This is in accord with the experimental evidence.
New evidence for molecular entanglements
Authors: Plazek D. J. , Raghupathi N. , O'rourke V. M. 
Published: April 2003

AbstractTorsional creep and creep recovery measurements have been made on a 56% polymer weight solution of an extremely high molecular weight polystyrene (M = 4.4 × 107) in tri‐m‐tolyl phosphate and on the polymer itself after recovery both from relatively dilute and more concentrated solution in benzene by freeze drying. Although viscoelastic steady state was not achievable, an anomalously shorter rubbery plateau in the response of the bulk polymer relative to its solution was indicated. On the basis of the assumed presence of physical entanglements of the threadlike molecules, which determine the length and height of the rubbery plateau, it was predicted and confirmed that the undiluted polystyrene recovered from dilute solution would have the highest and shortest creep compliance plateau.
Manifestation of microgel‐like particles of styrene‐ethylene dimethacrylate copolymers in solution in 1H and 13C NMR spectra
Authors: Spêváĉek J. , Duŝek K. 
Published: April 2003

AbstractFrom the integrated intensities of 1H NMR bands it has been found that in solutions of styrene (St)‐ethylene dimethacrylate (EDMA) copolymers, a considerable part of the monomer units do not show directly in high‐resolution 1H NMR spectra and it is suggested that these monomer units form compact structures, probably acting as cores of microgel‐like particles. In 13C NMR spectra all monomer units are shown, including those which are part of the compact microgel structures. From a comparison of 1H NMR spectra with other analytical methods (elemental analysis, infrared spectra) it follows that the composition of the copolymer in the core of the microgel is the same as the overall composition of the copolymer. The content of the compact structures in the microgel increases with the content of the EDMA component. The results are discussed from the point of view of structural features and of the motional restrictions of the St/EDMA copolymers in CCl4 solution. The consequences for 1H NMR analysis of copolymer composition are also discussed.
Effects of memory on the coherent scattering function for the rouse–zimm model of dilute polymer solutions
Authors: Fesciyan Sezar , Jhon Myung S. , Dahler John S. 
Published: April 2003

AbstractWe study the effect of the memory function on the coherent scattering function of a dilute polymer solution, taking into account hydrodynamic interactions among the polymer segments. The line shape, given by a sum of two exponentials, is very accurate numerically for ka ≳ 3 (with a the length of a polymer segment) and for times such that ω0(k)t ≲ 1.5 [with ω0(k) the initial slope]. However, this approximation to the scattering function is not nearly so accurate at the smaller values of ka encountered in light scattering experiments. The amplitudes and relaxation times associated with the two exponentials are found to be markedly dependent on the strength of the hydrodynamic interactions.
Vibrational spectra and normal coordinate analysis of trans‐1,4‐poly(2,3‐dimethylbutadiene) and the two polymorphic forms of trans‐1,4‐poly(isoprene)
Authors: Petcavich R. J. , Coleman M. M. 
Published: April 2003

AbstractThe infrared and Raman spectra of the two polymorphic forms of trans‐1,4‐poly(isoprene) (TPI) and trans‐1,4‐poly(2,3‐dimethyl butadiene) (TPDMB) are presented. Infrared spectra of the alpha and beta forms of TPI were obtained by digitally subtracting the amorphous contribution from the corresponding spectra of semicrystalline TPI polymers. Normal coordinate calculations are presented for both polymorphic forms of TPI and TPDMB, and the assignments of the normal modes are discussed.
Side‐chain crystallinity, heat of melting, and thermal transitions in poly[N‐(10‐n‐alkyloxycarbonyl‐n‐decyl)maleimides] (PEMI)
Authors: De La Campa J. I. González , Barrales‐Rienda J. M. , Ramos J. González 
Published: April 2003

AbstractThe heat of melting, the melting temperatureTm, and the sub‐Tgtransition temperature have been studied from –120°C to aboveTmin a series of 11 poly[N‐(10‐n‐alkyloxycarbonyl‐n‐decyl)]‐maleimides (PEMI). Side‐chains from ethyl to n‐docosyl withneven have been included. The contribution to the heat of melting per methylene group shows that the hexagonal paraffin crystal modification is present in these poly(N‐maleimides), in agreement with x‐ray data for the same compounds. The enthalpy data show that only a part of the outer methylene groups are present in the crystalline aggregates. Furthermore, DSC traces exhibit a typical distribution of crystallite sizes, which become narrower as the side‐chains become longer. The critical chain length needed to form a stable nucleus includes nine methylene groups in the outer part of the n‐alkyl side‐chain. The influence of the side‐chain length and crystallinity on the γ‐transition temperature of these polymers was also investigated. In the range where these polymers are essentially amorphous the sub‐Tgtransition temperature decreases continuously as the number of methylene groups in the side‐chain increases. This transition is attributed to internal motion within the external side‐group without any interaction with the main chain. This is presumably made possibly by the partial rotation of the oxycarbonyl group. We suggest that this transition is similar to the well known γ transition which has been attributed to various segmental motions in all ethylene copolymers and in all homopolymers containing a determined number ofCH2units in the main‐chain or in the side‐chain. Estimates based on the chemical structure, yield a value for the γ transition of CH2similar to that measured by other methods in polyethylene and related materials.
Heat capacity of a polydiacetylene single crystal from 3 to 300 K
Authors: Engeln I. , Meissner M. 
Published: April 2003

AbstractHeat capacities Cp of a polydiacetylene‐bis(toluene sulfonate) single crystal and its monomer have been measured in the temperature range from 3 to 300 K. The temperature dependence of Cp for both monomer and polymer crystals differs from that for monoatomic solids. By applying a chain lattice model for a polymer crystal, the temperature dependence of the heat capacity can be described assuming a phonon density of states given by bending and stretching modes of the polymer backbone. With a combination of one‐dimensional and three‐dimensional elastic continuum approximations, the heat capacity has been calculated and a good fit to the data has been obtained. A small peak in Cp was detected at 161 K for the monomer and at 198 K for the polymer. This may be ascribed to a lower‐temperature phase transition in the polydiacetylene crystals evidenced by previous x‐ray and spectroscopic measurements.
Incompatible blends: Thermal effects in a model system
Authors: Harrison Ian R. , Runt J. 
Published: April 2003

AbstractThere has been a growing interest in compatible blends in which one of the polymers is crystallizable. At appropriate compositions some of this polymer will crystallize, the remainder forms a compatible blend with the other polymer component; attempts have been made to relate melting point depression of the crystalline component to diluent effects, i.e., polymer/polymer interactions. Melting point is also a function of lamella thickness, the determination of which is very difficult in such systems. It is assumed in this type of study that the melting point of a crystal in an incompatible matrix will be unchanged. In an attempt to test this assumption we have determined the melting behavior of isothermally grown, single crystals of polyethylen (from the same preparation) embedded in a variety of incompatible matrices. The matrices used were polybutadiene, polystyrene, and polyphenylene oxide. This work shows that polymer single crystals embedded in an incompatible polymer matrix can show apparent melting point depressions of up to 5°. This size of depression represents a significant part of that reported for compatible systems.
Chemical analysis of vinyl‐crosslinked poly(dimethylsiloxane) model networks and use of the resulting structural information in the interpretation of their elastomeric properties
Authors: Llorente M. A. , Andrady A. L. , Mark J. E. 
Published: April 2003

AbstractModel networks were prepared by selective crosslinking through vinyl groups occurring as either chain ends or as side‐groups on a poly(dimethylsiloxane) backbone. Iodometric titrations were used to determine the number of unreacted groups, thereby providing detailed information on the completeness of the reactions and the structure of the resulting networks. The end‐linking reaction of the vinyl‐terminated chains was generally found to be at least 95% complete. In the case of very high junction functionality, however, the extent of reaction was significantly lower, presumably because of steric interferences in the vicinity of the junctions, as was concluded in a previous investigation. Lower extents of reaction were also found in the case of vinyl groups located along the chains, probably because such groups are constrained by two chain sequences instead of one. The equilibrium elastomeric properties of both types of networks were interpreted using the structural information thus obtained and were found to be in good agreement with previous experimental results. They are also in satisfactory agreement with theory, without introduction of the highly questionable assumption of large contributions from interchain entanglements.