bluuebunny/crossref_metadata_2025 huggingface dataset:
NMR of dissolved water in ultrathin and thick membranes of cellulose acetate
Authors: Krishnamurthy S. , McIntyre D. , Santee E. R. , Wilson C. W.
Published: April 2003

Wide‐line proton magnetic resonance spectra of thick (100 μ) and ultrathin (0.25 μ) membranes of cellulose acetate have been obtained in the “bone‐dry” state and in the wet state up to 2.5% water by weight. The NMR spectra were recorded with the membrane face aligned parallel and perpendicular to the magnetic field direction. The first derivative spectra of wet thick membrane (above 0.4% water) show a sharp center peak and at least one broad outer peak, both in the parallel and perpendicular orientations. The spectra of wet ultrathin membrane, on the other hand, show a pseudodoublet in the perpendicular orientation and a broad singlet in the parallel orientation. The differences in the spectra of the thick and ultrathin membranes are discussed in terms of “free” and restricted water believed to arise from the differences in the structure of thick and ultrathin membranes.
Pulsed NMR study of molecular motion in the diglycidyl ether of bisphenol‐A cured with 4,4′‐methylenedianiline
Authors: Larsen David W. , Strange John H.
Published: April 2003

The monomeric diglycidyl ether of bisphenol‐A cured with methylenedianiline has been studied by pulsed NMR. Values of the proton relaxation times T1, T1p, and T2 have been measured over the temperature range −160 to 200°C. The system was studied after being fully postcured at 180°C and after being cured at 100°C and at 54°C. The relaxation times are interpreted in terms of molecular motion in the cured resins, i.e., methyl group reorientation, segmental motions, and general molecular motion. The results are compared with those obtained previously by us for the uncured resin. Correlation frequencies for the segmental motions are compared with those obtained from dielectric relaxation and mechanical loss studies. There are at least two principal segmental motions present in the cured system, and the nature of these motions is found to depend on the cure temperature. These effects are discussed in terms of crosslinking and annealing of the system.
Thermodynamics of n‐alkane systems and the solution theories of flory and prigogine
Authors: Hammers W. E. , De Ligny C. L. , Vaas L. H.
Published: April 2003

The partial molar excess free enthalpies and enthalpies as well as the molar excess enthalpies of a number of n‐alkane systems were reexamined within the scope of the polymer solution theory of Flory, Orwoll, and Vrij and that of Prigogine in the version after Delmas, Patterson, and Somcynsky. A semiempirical method was used to obtain characteristic n‐alkane data, which obey the principle of corresponding states. By using these data (instead of those from the partition function after Flory and collaborators), a physically realistic interpretation of the excess free enthalpies over the whole concentration range is possible if the combinatorial contribution is purely athermal in nature. Both theories give an enthalpy interaction parameter near zero as expected, whereas neither a significant end effect nor an entropic interaction contribution is apparent from the analyses of the excess free enthalpies. The poor results obtained for the partial excess enthalpies and the enthalpies of mixing reflect the inadequacy of the partition functions on which these modern solution theories are based.
Spectroscopic method for the analysis of polyalkenamers
Authors: Tosi Camillo , Ciampelli Federigo , Dall'Asta Gino
Published: April 2003

A method based on use of NMR and infrared spectroscopy is described for the quantitative determination of the structural units generally occurring in polyalkenamers. The possibilities offered by both techniques are pointed out: in particular, the values found for the absorptivities of the infrared bands typical of unsaturated alkenamer units are extensively discussed.
Effect of the reference chain dimension on the viscoelastic and stress–strain behavior of poly(n‐butyl methacrylate) networks
Authors: Ilavský M. , Hasa J.
Published: April 2003

The linear viscoelastic and stress‐strain behavior of poly(n‐butyl methacrylate) networks at a content of crosslinking agent (ethyleneglycol dimethacrylate) of c0–1 × 10−4 mole/cm3 was investigated in the main transition and rubberlike region in the temperature interval from 20 to 150°C. The dependence of the unperturbed chain dimensions on temperature was determined from thermoelastic measurements in the rubberlike region; this dependence was unaffected by the content of crosslinking agent. Application of time–temperature superposition to the linear viscoelastic behavior did not give a continuous superimposed curve in the proximity of the rubberlike region; superposition within the whole time region required introducing the change of the unperturbed chain dimensions with temperature. This correction was sufficient for a sample with a higher content of the crosslinking agent. However, for loose networks (c< 0.1 × 10−4 mole/cm3) it was insufficient, because of another relaxation mechanism in the region of high temperatures. It was found that the intensity and temperature dependence of this relaxation mechanism, which is probably due to a change of the number of entanglements with temperature, are connected with the magnitude and the temperature dependence of the C2 constant of the Mooney‐Rivlin equation.
Numerical calculations of the viscoelastic properties of solutions of branched polymers based on the Zimm‐Kilb theory
Authors: Osaki Kunihiro , Schrag John L.
Published: April 2003

Numerical calculations were performed for the viscoelastic properties of dilute solutions of branched star polymers with equal branch lengths as formulated in terms of a bead‐spring model by Zimm and Kilb without using the integrodifferential equation approximation method to calculate the eigenvalues. The complex modulus and complex viscosity were calculated as functions of frequency for various combinations of the number of branches f (4, 8, and 13), the number of beads in one branch Nb (= N/f; 20 to 100, where N + 1 is the total number of beads, N the number of springs in the molecule) and the reduced hydrodynamic interaction parameter h* (= h/N1/2 0.05 to 0.3, where h is the hydrodynamic interaction parameter of Zimm and Kilb). The frequency dependence of the complex modulus in the low‐frequency range depends mainly on h* and not on Nb if Nb is large enough, and it is very close to that calculated from the eigenvalues for h→∞ obtained by Zimm and Kilb, if h* is about 0.25. As h* decreases from 0.25, the frequency dependence gradually approaches that of the free‐draining cash (h→0). Calculations may be carried out for h* values somewhat larger than 0.25 and result in a frequency dependence that is not intermediate to the h → 0 and h → ∞ cases as evaluated by Zimm and Kilb. The physical meaning of such “super‐non‐free‐draining” values of h* is uncertain, however. The intrinsic viscosity ratio g′ = [η]f/[η]lin is an increasing function of h* and changes very slowly with N. For h* = 0.25, g′ is close to the non‐free‐draining limit for any value of N.
Raman spectral changes during the solid‐state polymerization of diacetylenes
Authors: Melveger A. J. , Baughman R. H.
Published: April 2003

Raman spectral changes resulting from the solid‐state 1,4‐addition polymerization of conjugated diacetylenes are reported. The monomers show an intense CC stretching frequency near 2260 cm−1, where as the polymers showed two strong bands, a CC vibration near 2100 cm−1 and a CC vibration near 1500 cm−1. The presence of both double and triple bonds in the polymers suggests the backbone structure (CCCC)n. The alternate mesomeric structure (CCCC)n can be eliminated as a possibility by the presence of the strong CC vibration in the polymer. Sequential Raman spectra obtained during radiation‐induced polymerization revealed intermediate spectral states between the initial monomer and final polymer. Intermediate‐state vibrations first increase and then decrease in intensity as polymerization proceeds. However, the observed vibtrational frequencies of intermediate states were not dependent upon the extent of polymerization. Whether polymerization occurred thermally or as a result of radiation did not appear to influence the spectrum of the final polymer, but the observed number of intermediate states differed. Polymerization mechanisms, required molecular motions, and resulting structural changes are discussed.
Conformational energies, stereoregularity, and the role of nonstaggered conformations in polymer chains
Authors: Flory Paul J.
Published: April 2003

The role of nonstaggered conformations in polymethylenes and in vinyl polymers is discussed in some detail. In incorporating such conformations into rotational isomeric state treatments, it is essential to so choose rotational states as to assure equitable sampling of configuration space. Tacit identification of rotational states with minima in the conformation energy surface, a common practice at present, may lead to serious errors. The significance and limitations of conformational energy calculations are discussed. It is pointed out that the alleged discrepancy between theory and experiments on the spatial configurations of isotactic polymers of α‐olefins in general and of polypropylene in particular is unsupported by valid experiments on polymers of established stereochemical constitution.
Dielectric relaxation of collagen and gelatin
Authors: Chang E. P. , Chien James C. W.
Published: April 2003

Dielectric dispersions of reconstituted collagens and gelatin were measured from 0.1 to 10 kHz and −160 to +160°C. At 0.1 kHz there is a γ transition at −80°C which is attributed to the H2O‐coupled local modes. The process has an activation energy of 7.5 kcal. A devitrification process is observed at 10–20°C. Both of these processes have their counterparts in the dynamic mechanical measurements. The tan δ values are up to 3 times as great for the dynamic mechanical dispersions. There is an additional hightemperature dielectric loss transition which does not correspond to any seen with the mechanical experiments. A probable mechanism for this absorption is the Maxwell‐Wagner‐Sillars effect.
Roughness and anisotropy effects on wettability of polytetrafluoroethylene and sodium‐treated polytetrafluoroethylene
Authors: Cirlin Eun Hee , Kaelble David H.
Published: April 2003

The effect of roughness on wettability of skived polytetrafluoroethylene (PTFE or Teflon) and Na‐treated PTFE film were studied by advancing contact angle measurements. The effect of an anisotropic force field of elongated Na‐treated PTFE on the shear bond strength were also studied as a function of elongation. The results are analyzed in terms of London dispersion γsd and Keesom polar γsp contributions to surface energy γs.

It was found that the roughness effect on wettability of PTFE is significant for untreated PTFE and negligible for Na‐treated PTFE. Our shear bond strength σb analysis of elongated Na‐treated PTFE showed that σb is influenced by an anisotropic force field and the σb increases with the fractional polarity p = γsp/γs but decreases with the dispersion fraction d = γsd/γs of solid‐vapor surface tension γs = γsd + γsp
An entanglement model for the dependence of fracture surface energy on molecular weight
Authors: Moon P. C. , Barker R. E.
Published: April 2003

Over the last decade, empirical evidence has indicated that the effective surface energy γ associated with the fracture of noncrystalline is a linear function of the reciprocal of the viscosity–average molecular weight: \documentclass{article}\pagestyle{empty}\begin{document}$ \gamma = \gamma _\infty - b\bar M_v ^{ - 1} $\end{document}. For poly(methyl methacrylate), data of J. P. Berry, G. C. Berry and Fox show that gamma; ∼ 0 at about the same value of M̄v that corresponds to the polymer chain‐entanglement length. From this fact, we have developed an entanglement network model for fracture, that bears a resemblance to F. Bueche's entanglement model for the melt viscosity of bulk polymers. Our model allows for the expression of the previously empirical constants, γ∞ and b, in terms of molecular parameters: \documentclass{article}\pagestyle{empty}\begin{document}$ {{\gamma _\infty = \gamma _{\rm s} A_{\rm s} Z_{\rm c} \rho _{\rm c} N_A } \mathord{\left/ {\vphantom {{\gamma _\infty = \gamma _{\rm s} A_{\rm s} Z_{\rm c} \rho _{\rm c} N_A } {\bar M_{\rm s} }}} \right. \kern-\nulldelimiterspace} {\bar M_{\rm s} }} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ b = 2({{\bar M_v } \mathord{\left/ {\vphantom {{\bar M_v } {\bar M_n }}} \right. \kern-\nulldelimiterspace} {\bar M_n }})\gamma _\infty M_{\rm f} $\end{document} where M̄n and M̄f are the number‐average molecular weights of the polymer and of the free chain ends, M̄v is the viscosity‐average molecular weight, γs is the average fracture‐energy per entanglement in the craze volume, As is the average cross‐sectional area of the polymer chain, Zc and ρc are the thickness and density of crazed material on the fracture surface, respectively; M̄s is the average strand molecular weight between entanglements, and NA is AvogadrO's number.
Morphology of injection‐molded polypropylene
Authors: Fitchmun D. R. , Mencik Z.
Published: April 2003

A surface zone composed of at least three distinct layers has been detected in injection‐molded polypropylene. The morphology of these layers as determined by optical and scanning electron microscopy forms a continuous picture from the “as‐molded” surface to the core. With the exception of the first layer which is always featureless, the observed morphology is mostly spherulitic. Starting in the second layer, the spherulites decrease steadily in size until they reach a minimum somewhere near the middle of the third layer. After passing this point, they increase in size—rather rapidly—as the boundary between layer 3 and the core is approached. In samples prepared at the shorter fill times, the spherulites continue to decrease in size until they are replaced by the mixed matted straw–flat plate texture. The overall morphological features of this surface zone are explained by using an extension of a model for the crystallization of a quiescent polymer melt. In this model, growth originates from heterogeneous nuclei whose density varies throughout the sample as a function of both a temperature gradient and the induction time. Interpretation of anomalies in the fine structure of the individual layers indicates that shear is influencing the crystalline morphology also.
Environmental stress cracking of polyethylene
Authors: Schonhorn Harold , Frisch H. L. , Albarino R. V.
Published: April 2003

Modification of the Griffith theory for the presence of liquids has been shown to explain some facets of the environmental stress cracking of polyethylene. In the absence of intercrystalline links and tie molecules, we find that one important factor is the interfacial tension generated between the spherulite boundary and the liquid environment. Judicious incorporation of silanes into polyethylene appear to reduce the tendency to stress cracking by modifying the interfacial tensions between the environment and the polymer.
Crystal structure of nylon 12
Authors: Inoue Kazuo , Hoshino Sadao
Published: April 2003

The crystal structure of nylon 12 prepared by polymerization of dodecalactam has been determined by x‐ray diffraction. Nylon 12 fiber exhibits only the γ form as its stable crystal structure. The unit cell of nylon 12 was determined with the aid of the x‐ray diffraction pattern of a doubly oriented specimen. The unit cell is monoclinic with a = 9.38 Å, b = 32.2 Å (fiber axis), c = 4.87 Å and β = 121.5° and contains four repeating monomer units. The chain is planar zigzag for the most part but is twisted at the position of amide groups, forming hydrogen bonds between neighboring parallel chains. The chain conformation is similar to that of the γ form of nylon 6 proposed by Arimoto. It was deduced from the calculations that there are two chain conformations statistically coexistent according to the direction of twisting. In each conformation, hydrogen bonds are formed between parallel chains to make pleated sheetlike structures. The sheets are nearly parallel to (200) and in the sheet the directions of the neighboring chains are antiparallel, as is the case with nylon 6.
Lower‐frequency infrared spectra and structures of some typical aliphatic polyamides
Authors: Matsubara Ikuo , Magill J. H.
Published: April 2003

The Polarized lower‐frequency infrared spectra (800–33 cm‐1) of nylon 66 (α form), nylon 77 (γ form), and nylon 6 (both α and γ form) have been examined. The spectral changes which occur on complex formation of the polyamides with iodine‐potassium iodide solution and on subsequent iodine desorption have been studied in relation to the changes in the polymer structures. On the basis of these results, most of the stronger bands have been reasonably assigned to the vibrations characteristic of the amide group and the methylene chain of the polyamides, and some new structure–frequency correlations have been established for the polymers.
Small‐angle x‐ray scattering experiments for investigating the validity of the two‐phase model
Authors: Strobl G. R. , Müller N.
Published: April 2003

A New method for evaluating SAXS curves of polymer samples with lamellar structure is applied to two typical scattering curves measured with a solution‐crystallized linear polyethylene and a melt‐crystallized branched polyethylene respectively. The method permits a rigorous check of the validity of the two‐phase model and yields, without additional measurement, the volume fractions of the two phases and the difference in their densities. The densities can than be obtained by measuring the overall density of the sample. The results are: ρc = 0.996 g/cm3,ρa = 0.854 g/cm3, wa = 0.20 for the solution‐crystallized sample; ρc = 0.967 g/cm3,ρa = 0.850 g/cm3, wa = 0.36 for the melt‐crystallized sample.
Interpretation of the heat capacity of polymer melts
Authors: Bares Vera , Wunderlich Bernhard
Published: April 2003

Heat capacity values for melts of polystyrene, poly(methyl methacrylate), polypropylene, and polyethylene are calculated on the assumption that the total constant‐volume heat capacity Cv is made up of two parts: one associated with molecular vibrations, and one, with holes. Numerical values of both components are given for a wide range of temperatures and compared with experimental data. For poly‐1‐butene insufficient data for complete evaluation are available, so that only the vibrational contribution could be discussed.
Energetics of phase transformations in polyethylene
Authors: Yemni Tarik , McCullough R. L.
Published: April 2003

The molecular mechanisms involved in the orthorhombic‐to‐monoclinic phase transformation in polyethylene were investigated by the computer simulation of a structure–energy map based on empirically justified intermolecular potential functions. Stable packing structures for the orthorhombic and monoclinic form were isolated as relative minima, cohesive energies were determined from the energy minima, specific chain motions involved in the transformation were identified by the minimum energy path connecting the packing minima, and the activation energy for the transformation was determined from the energy barrier along the minimum energy transformation path. The packing structure parameters predicted from the energy map were in excellent agreement with unit cell dimensions observed near 0°K. The activation energy predicted for the transformation is relatively low (∼0.5 kcal/mole of ethylene at 0°K and 0.25 kcal/mole of ethylene near the melting point, 411°K). Monoclinic packing was predicted to be slightly more stable than orthorhombic. Since this result is inconsistent with a large body of observations, we propose that the intramolecular energy of chain folds plays a dominant role in establishing chain‐packing geometry. The inclusion of fold‐transition energetics could give rise to transformation mechanisms which differ in details from those proposed in this work.
Characterization and properties of macromolecules. III. Gel‐permeation chromatography: The effect of temperature upon the elution volume and the efficiency of the separation process
Authors: Cooper A. R. , Bruzzone A. R.
Published: April 2003

We report the first study of the effect of temperature on the elution volume and efficiency of the gel‐permeation chromatographic (GPC) process with the use of porous glass column packings. Monodisperse polystyrenes and narrow fractions of polyisobutenes were used as solutes and 1,2,4‐trichlorobenzene as the eluting solvent. This study has been made possible by the development of a successful method of eliminating the adsorptive properties of the glass surface with hexamethyldisilazane. Previously, without glass treatment, polystyrene would not elute from this system at 150°C. Previous studies dealing with this topic have been limited to the use of polystyrene gel column with ill‐defined temperature–structure behavior. Several measures of polymer dimensions have been correlated with the GPC elution volumes to ascertain which best reduces the data to a common calibration for these linear chains.
Analysis of flow behavior of polyethylenes and polypropylenes with graessley's theory
Authors: Saeda Shigeru
Published: April 2003

Graessley's theory of non‐Newtonian behavior of linear polymers is tested with data on polyethylenes and polypropylenes having a wide range of molecular weights and molecular weight distributions, and for a polyethylene fraction. Theoretical flow curves derived by using molecular weight distribution data from column fractionations are in good agreement with experimental curves obtained from a cone‐and‐plate viscometer and an extrusion‐type rheometer, when the distribution is assumed to cut off at a maximum molecular weight. The experimentally obtained relaxation time for entanglement is found to be proportional to the Rouse relaxation time, though the former is about one decade smaller than the latter.
Crystallization kinetics of biaxially stretched natural rubber
Authors: Oono Ryo , Miyasaka Keizo , Ishikawa Kinzo
Published: April 2003

The isothermal crystallization of natural rubber was investigated under biaxial stretching. A marked planar orientation of crystals occurs in such a way that the (010) plane orients parallel to the film plane. The rate of crystallization increases with the biaxial stretching ratio, and the Avrami exponent n decreases. At the highest extension, n becomes less than unity. The equilibrium degree of crystallinity decreases with the stretching ratio. The crystallinity was less than 10% for the highest extension. The melting behavior is similar to that in uniaxial stretching.
Dielectric and ultrasonic studies of the δ‐relaxation of poly(ethyl methacrylate)
Authors: Shimizu Kazuharu , Yano Okimichi , Wada Yasaku , Kawamura Yasuaki
Published: April 2003

Complex dielectric constants at frequencies of 110 Hz, 1 kHz, and 10 kHz and complex elastic moduli at 34 kHz and 3 MHz were measured in the temperature region the of δ relaxation of poly(ethyl methacrylate) (PEMA) down to 4°K. The temperatures of the loss maximum correlate well with literature values of the temperatures of mechanical loss maxima and with T1 minima. The activation energy is 2.1 kcal/mole. The energy map for the internal rotation of the ester ethyl group of PEMA was calculated; the activation energy and the energy difference between the two energy minima (0.31 kcal/mole) were found to agree well with those determined from experiment. The strength of dielectric relaxation is interpreted on the basis of 0.11 D as the dipole moment of the ethyl group. The strength of mechanical relaxation obtained in the present study as well as the previously published values are discussed. The volume change arising from the internal rotation of an ethyl group is found to be comparable at low temperatures with the van der Waals volume of the ethyl group and to decrease with increasing temperature.
Diffusion and reaction in polyester melts
Authors: Pell T. M. , Davis T. G.
Published: April 2003

An understanding of the physical and chemical processes involved in the melt polymerization of polyesters in the higher inherent viscosity ranges is of fundamental importance in polyester preparation. For example, the volatile condensation product must diffuse to a polymer–vapor interface before polymerization can take place. Thus, the rate of polymerization of a polyester may be dependent not only upon the chemical kinetics of the polymerization reaction but also upon the diffusion of the condensation product through the polymer melt. The objective of the work presented in this paper was to determine to what degree diffusion or reaction kinetics, or both, limit the melt polycondensation of poly(ethylene terephthalate). Degrees of polymerization in melts between 0.0285 and 0.228 cm in depth at 270°C were measured for various reaction times and were compared with the predictions of mathematical models. The polycondensation rates under these conditions depend upon both the polycondensation rate constant k1 and the diffusivity D of ethylene glycol through the melt. Estimates of the values to these parameters are: k1 = 0.0500 (moles/mole of repeat unit)−1 sec−1; D = 1.66 × 10−4 cm2/sec.
Thermal degradation of cellulose in nitrogen
Authors: Dollimore D. , Holt B.
Published: April 2003

The thermal degradation of four different forms of cellulose in nitrogen has been studied by using a thermobalance. In TG experiments a total weight loss at 900°C was 80% in the cases of film and pulp samples and 83% for two powder forms. The results for the isothermal degradation of the four samples at 270°C are plotted as degree of degradation α against reduced time t/t0.5 and compared with the master plots of Sharp, Brindley, and Achar. The experimental data fit most closely the plot for the Avrami‐Erofeev equation in the form kt = {–ln (1–α)}1/n where n = 2. An activation energy of 144 kJ/mole has been found for the degradation of one of the celluloses from the results of isothermal runs at six different temperatures. It is postulated here that the thermal degradation occurs by random nucleation and nucleus growth in the cellulose fibrils so as to yield a carbon whose microporous structure is a replica of the pore system in the parent cellulose.
Studies of polymer blends. I. Compatibility of poly(vinyl chloride) and poly(ethylene‐co‐vinyl acetate‐co‐sulfur dioxide)
Authors: Hickman James J. , Ikeda Richard M.
Published: April 2003

Various methods of determining polymeric molecular compatibility were applied to blends of poly(vinyl chloride) (PVC) and poly(ethylene‐co‐vinyl acetate‐co‐sulfur dioxide) (E/VA/SO2). In one series, where the E/VA/SO2 had a mole composition of 72.7/18.5/8.8, true compatible blends were demonstrated by phase‐contrast microscopy, torsion pendulum studies, and differential scanning calorimetry experiments for blends containing up to 40% E/VA/SO2. These blends exhibited a single Tg whose compositional variation was found to follow the Fox expression. Experimental densities were slightly greater than predicted on assuming volume additivity. This observation implies better packing and a negative heat of mixing and thus is in harmony with a negative free energy of mixing and the observed molecular compatibility.
Chain‐folding measurements in annealed poly(ethylene terephthalate)
Authors: Mehta R. E. , Bell J. P.
Published: April 2003

Chain folding in unoriented poly(ethylene terephthalate) (PET) films has been investigated as a function of annealing time and temperature. To meet this objective dynamic mechanical, infrared, and molecular weight measurements were used, together with selective chemical degradation to remove chain folds and amorphous regions. The β dispersion in the dynamic mechanical spectrum of PET is here tentatively associated with motions of methylene and/or carboxyl groups in irregular chain folds; the β dispersion is not found in quenched amorphous polymer, in polymer where amorphous regions and chain folds have been removed, or in highly annealed PET where the irregular folds have regularized. Upon mild crystallization and annealing (30 min at 110°C) of initially amorphous film a large β dispersion appears and then diminishes upon further annealing at 220°C. As the β dispersion diminishes, the infrared regular fold band increases more than the crystallinity band, indicating regularization of folds. The molecular weight of the degraded residue corresponds approximately to typical fold‐period dimensions (∼130 Å), and increases on annealing as expected from lamellar thickening. The degradation process has, by fold removal, reduced the chains in the crystals to a very short, uniform length.
Solution properties of polymers of pyridinium and ammonium methacrylates
Authors: Stejskal Jaroslav , Beneš Milan J. , Kratochvíl Pavel , Peška Jan
Published: April 2003

Solution properties of poly[1(2‐hydroxyethyl)pyridiniumbenzene sulfonate methacrylate] and poly[1(2‐hydroxyethyl)trimethylammoniumbenzene sulfonate methacrylate] were studied. Within a certain concentration range of some added low molecular weight electrolytes, phase separation occurs. The dependence of intrinsic viscosity on molecular weight was determined and the steric factor estimated for both polymers. For nonaqueous solvents, an extrapolation of the dependence of the refractive index increment of the polymer on the refractive index increment of the polymer on the refractive index of the solvent leads to an apparent refractive index of the polymer, different from the refractive index determined directly by the immersion method. Some peculiarities of light scattering in solutions with no electrolyte added are mentioned.
Heat capacity of amorphous polyhexene‐1 between 20 and 300°K: Intramolecular vibrational contribution to Cvbelow the glass transition
Authors: Bourdariat J. , Isnard R. , Odin J.
Published: April 2003

The heat capacity of polyhexene‐1 was measured between 20 and 300°K. The apparatus, an adiabatic calorimeter giving results with a random error of 0.2–0.4%, is briefly described. The characterization of the sample by x‐ray diffraction patterns established that it was amorphous at all temperatures. Gold foil was incorporated with the sample to increase the apparent thermal diffusivity and so to decrease the time needed for the measurements. The glass transition temperature was found to be 215.5 ± 1°K. On theCpcurve, no subglass anomaly was detected, unlike the results of experiments described elsewhere. The calculation ofCvis discussed, and an explanation is given for the choice of the number of intramolecular vibrational modes per monomer which are assumed to contribute toCv. A linear continuum model with characteristic temperature θ1= 736°K allows us to fit the experimental curve over a temperature range of 140°K.
A theory for environmental craze yielding of polymers at low temperatures
Authors: Brown Norman
Published: April 2003

It has been recently discovered that polymers craze at low temperatures in the presence of nitrogen or argon. A quantitative theory has been developed which explains (1) the critical temperature above which the phenomenon disappears, (2) the critical stress for nucleating a craze, (3) the effect of strain rate on the yield point and size of crazes, (4) the drop in the load during craze yielding, and (5) the increase in strength of the polymer in N2 or Ar at high strain rates so that the ultimate strength may exceed that in He or vacuum. The crazing action of the gases is described qualitatively at the molecular level.
Annealing effects in poly(vinylidene fluoride) as revealed by specific volume measurements, differential scanning calorimetry, and electron microscopy
Authors: Nakagawa Koichi , Ishida Yoichi
Published: April 2003

Specimens of poly(vinylidene fluoride), crystal form II, annealed at different temperatures between 130 and 180°C were characterized by specific volume measurements, differential scanning calorimetry (DSC), and electron micróscopy. The degree of crystallinity calculated from the specific volume changed only by 15% i.e., from 50% to 65%. On the other hand, the melting behavior changed with annealing conditions. When a specimen was annealed above 170°C, two endothermic peaks appeared on either side of the annealing temperature. Results from DSC measurements made at different heating rates and electron microscopy showed that the two endotherms were caused by a bimodal distribution of lamellar thicknesses. The equilibrium melting point was found to be 210°C from the linear relation of the melting point and the annealing temperature. The equilibrium enthalpy and entropy of fusion were found to be 1.6 keal/mole and 3.3 eu/mole of repeat units by measurement on polymer–diluent mixtures. The surface free energy was found to be 5.1 kcal/mole of lamellar sequences from the plot of melting point versus reciprocal lamellar thickness obtained by electron microscopy. From a plot of enthalpy of fusion versus reciprocal lamellar thickness the surface enthalpy was found to be 20 keal/mole of lamellar sequences. These data lead to the estimate that a chain fold consists of about 30 repeat units.
Shear bands in polycarbonate
Authors: Wu W. , Turner A. P. L.
Published: April 2003

Lexan polycarbonate specimens in the form of tubes were deformed in torsion. The deformation occurs by the nucleation and growth of discrete shear bands. Shear bands are initially formed at the upper yield point. Development of the bands is accompanied by a drop in the stress to a lower yield point. At the lower yield point the strain inside the bands is approximately 70% and remains constant thereafter. Further deformation occurs by growth of the bands until they cover the entire sample. When the direction of twisting is reversed after the shear bands are formed, the deformed material untwists uniformly, without deformation in the previously undeformed material, and the stress required for untwisting the deformed material is lower than the stress required to propagate the band into undeformed material.
Polymer emissivity
Authors: Gay F. P.
Published: April 2003

The thermal emission characteristics of polypyromellitimides have been examined as a function of temperature by measurement of the power required to maintain steady‐state temperatures in an evacuated system. The emissivity was derived and found to increase with increasing temperature up to a saturation limit of above 0.9 at temperatures above 475°K. The effect is explained as a thermal population of excited infrared transitions. Power emitted is dominated by the most intense bands which are common to absorption and emission spectra.
Detection of “memory” effects in polyethylene by magnetic susceptibility
Authors: Phaovibul O. , Loboda‐Čačković J. , Hosemann R. , Baltà‐Calleja F. J.
Published: April 2003

The relevance of diamagnetic susceptibility as a tool for the structure analysis of solid high polymers is stressed in the light of some new examples. The present results complement previous data and offer new aspects on the diamagnetic investigations of longchain hydrocarbons, especially polyethylene (PE). The molecular susceptibility is proportional to the average number of repeat units in the chain. The proportionality factor defines an intermolecular constant μk which characterizes different physical states. This was found to be 2.5 × 10−6 for the liquid and 3.5 × 10−6 cgs for the crystalline state of paraffins and polyethylene (solution‐crystallized). For melt‐crystallized material, μk, approaches the typical value of the liquid paraffin in agreement with previous results. Such a low μk is probably related to the increased disorder of the paracrystalline lattice domains, in contrast to the more ordered microparacrystallites in the so‐called “single crystals,” where μk = 3.5 × 10−6. In single crystals of branched PE, μk approaches 2.5 × 10−6 with increasing branching ratio. Like paraffins in the gaseous state, molten PE, with chains longer than 1000 Å, has μk = 0. If the solution‐crystallized material is molten for 10 min and thereafter cooled, μk retains the original value 3.5 × 10−6 cgs characteristic of the crystalline state. Hence, solution‐crystallized polyethylene apparently possesses a kind of “memory.” Such a “memory” can, nevertheless, be partly destroyed when molten PE is stirred for 10 min and then quenched. Aggregates of solution‐precipitated crystals with 3% branching concentration give μk = 2.9 ± 0.2 × 10−6 in good agreement with x‐ray diffraction data. Finally, experimental details on the magnetic measurements are critically discussed, and various aspects of improvements for further investigations are also described.
ESR study of structural changes in high‐density polyethylene subjected to cyclic tensile stress
Authors: Nagamura Toshihiko , Kusumoto Naoshi , Takayanagi Motowo
Published: April 2003

Bulk‐crystallized high‐density polyethylene is subjected to cyclic tensile stress and then irradiated by γ‐rays to “spin‐label” polymer molecules. The change of crystalline texture in the fatigue process before initiation of necking is detected by the ESR method. The line‐resolution parameter of the ESR spectrum, which reflects the degree of regularity of molecular arrangement, first decreases, then increases somewhat, and finally becomes almost constant during fatigue cycling. The concentration of radicals trapped in a fatigued sample is larger than that in the unfatigued one. The excess radicals disappear during heating by a process of low activation energy in the temperature region of the mechanical γ dispersion. The degree of crystallinity evaluated from x‐ray diffraction and density scarcely changed during fatigue cycling. The size of the mosaic block crystals estimated from the radical trapping capacity showed a rapid decrease at the initial stage of fatigue. The x‐ray paracrystalline analysis indicates a similar but not so drastic decrease. These results lead to the conclusion that the slight disordering of crystalline texture accompanying the decomposition of mosaic block crystals in the lamellae occurs at the initial stage of the fatigue process, following which crystals reform somewhat and then remain unchanged until the initiation of necking.
Crystal structure of poly‐p‐xylylene. I. The α form
Authors: Iwamoto Reikichi , Wunderlich Bernhard
Published: April 2003

The molecular conformation and the crystal structure of α‐form poly‐p‐xylylene has been determined by x‐ray diffraction. The polymer has a monoclinic unit cell with a = 5.92, b = 10.64, c (fiber axis) = 6.55 Å, and β = 134.7°. Two chains pass through the unit cell, and the space groups is C2/m. The packing fraction is 0.705. One monomer unit makes up the fiber identity period and the internal rotation angles are 0° and 90° for the CH2CH2 and CH2ϕ bonds, respectively. All benzene rings are in parallel orientation, perpendicular to the ac plane.
Slow motion of long‐chain molecules in solution with internal correlations
Authors: Caroli B. , Saint‐James D. , Jannink G.
Published: April 2003

The Rouse equations for the dissipative motion of long‐chain molecules are reformulated in terms of coupled Langevin equations. While in the conventional Rouse model the random forces acting on each bead are supposed to be uncorrelated, the calculation given here admits of any correlation between the forces. By virtue of the second fluctuation dissipation theorem this corresponds to an added friction factor, called the “internal viscosity” in agreement with earlier work of Kuhn and Kuhn, Cerf, and of Peterlin. In the mode decomposition, this added friction factor happens to be an even function of the mode frequency. From this general model it is possible to compute formally the mean‐square displacement function. It takes a simple form if one assumes that forces are correlated only on adjacent beads and that their correlation functions are δ functions. The results of the calculation are best displayed in the Fourier transform of the meansquare displacement, which is directly related to the neutron incoherent scattering cross section. It is seen that the presence of internal viscosity modifies the behavior of the chain for a time scale of the order of the relaxation time of the elementary segment.
Decay of catalytic activity during the cationic polymerization of capryllactam
Authors: Puffr R. , Šebenda J.
Published: April 2003

At lower concentrations of initiator and temperatures above 200°C, the polymerization of capryllactam initiated by hydrogen chloride is characterized by two kinetically different stages: the initial rapid growth becomes considerably slower due to the fast transformation of the original growth centers into amidines. The steep decrease in molecular weight during hydrazinolysis indicates that the amidine groups are also present inside polymer molecules. The formation of these structures may be explained by condensation of the amino endgroups with the amide or acyllactam groups.
Stereochemistry of alternating methacryloyl‐L‐valine methyl ester–maleic anhydride copolymer
Authors: Nishihara Koji , Sakota Naokazu
Published: April 2003

The stereochemical composition of an alternating methacryloyl‐L‐valine methyl estermaleic anhydride (L‐MAVM/MAn) copolymer which was prepared by the photocopolymerization of L‐MAVM and MAn in dioxane at 25°C without initiator was investigated by proton magnetic resonance spectroscopy. The resonance of the ester methyl protons of the L‐MAVM unit appeared as three split peaks at 3.65, 3.76, and 3.82 ppm, which could be assigned to those of the coisotactic (di‐threo‐tri‐isotactic), coheterotactic and cosyndiotactic triads, respectively. The triad cotacticity determined according to these assignments indicated that the copolymer was composed predominantly of di‐threo‐tri‐isotactic triad. Similarly PMR spectroscopic investigation of the acryloyl‐L‐valine methyl ester–maleic anhydride (L‐AVM/MAn) copolymer with a 1:1 molar ratio of the monomers showed that the main tactic fraction of the copolymer was also di‐threo‐tri‐isotactic one. Nevertheless, the circular dichroic investigation of the L‐AVM/MAn copolymer before and after hydrolysis denied asymmetric induction into the polymer main chain. These results suggest that the propagation step in the photocopolymerization of L‐MAVM or L‐AVM with MAn proceeds by the trans‐trans opening of the complexmer composed of a 1:1 molar ratio of L‐MAVM or L‐AVM and MAn.
An application of spin trapping to radical polymerizations
Authors: Kunitake Toyoki , Murakami Shigeru
Published: April 2003

Radical polymerizations and copolymerizations were carried out in the presence of phenyl tert‐butyl nitrone(PBN) and tert‐nitrosobutane (t‐BuNO), and the structure of the spin adduct formed was investigated by ESR spectroscopy. PBN adducts gave the same ESR pattern, and the variation of the splitting constant was not large enough to warrant its use for the structure assignment. Therefore, the subsequent trapping experiments were performed with t‐BuNO. The polymerization mixture of representative monomers showed esr patterns that are indicative of the propagating radical being trapped. These trapped radicals were not necessarily very stable and, in most cases, disappeared after long reaction periods. In the case of α‐methyl substituted monomers, additional nine‐line spectra were observed which were attributed to trapping of the radical species formed by hydrogen abstraction from the α‐methyl group. The tert‐butyl radical which was formed by decomposition of t‐BuNo was probably responsible for the hydrogen abstraction. In the case of styrene, methyl acrylate, and methyl methacrylate, characteristic ESR patterns of the propagating radicals were observed with polymers which were prepared in the presence of t‐BuNO and purified by reprecipitation. Simultaneous trapping of different propagating radicals was attempted in several copolymerization systems. However, this was generally unsuccessful, because of the large difference in reactivities of the propagating radical with t‐BuNo.
Some aspects of graft polymerization of vinyl monomers onto cellulose by use of tetravalent cerium. IV
Authors: Mansour Olfat Y. , Nagaty Ahmed
Published: April 2003

Intense agitation markedly decreased the homopolymer formation in homopolymerization reactions. Graft polymerization is similarly influenced, the main effect being on the propagation process. The results achieved in this work indicate that in grafting reactions, growing polymer radicals are produced mainly through the transfer of radicals formed at the cellulose backbone to the monomer where propagation takes place. The growing polymer radicals either recombine with active sites on the cellulose leading to grafting or react with each other through coupling and/or are oxidized with ceric ions to give homopolymer.
New imidazoisoquinoline ladder polymers
Authors: Sicree A. J. , Arnold F. E. , Van Deusen R. L.
Published: April 2003

In previous studies on poly{(7‐oxo‐7, 10H‐benz[de]imidazo[4′,5′:5,6]‐benzimidazo‐[2,1‐a]isoquinoline‐3,4:10,11‐tetrayl)‐10‐carbonyl} it was observed that the polymer exhibits very unusual film‐forming properties. The ladder polymer forms supermolecular aggregates in solution which translates to a high degree of interchain packing in the bulk. New ladder imidazoisoquinoline polymers have been prepared in an effort to relate the variance of molecular structure to the aggregation behavior of this class of polymers. The polymers were prepared from the solution polycondensation of 1,4,5,8‐naphthalene tetracarboxylic acid or dianhydride with 1,2,5,6‐tetraaminonaphthalene, 2,3,7,8‐tetraaminophenazine and 2,3,7,8‐tetraaminodibenzofuran. It was found that the extent of interchain packing in the bulk is dependent to a large degree on the molecular geometry of the polymer backbone.
Studies on the photooxidation mechanism of polymers. I. Photolysis and photooxidation of polystyrene
Authors: Rabek Jan F. , Rånby Bengt
Published: April 2003

A new mechanism has been proposed for the photooxidation of polystyrene as film and in benzene. The initial stage of the photooxidative degradation may involve reactions of singlet oxygen with polystyrene molecules. Singlet oxygen may be formed in the reaction between excited benzene ring in polystyrene molecule and molecular oxygen. The addition of singlet oxygen quenchers such as 1,3‐cyclohexadiene or β‐carotene reduces the rate of polymer degradation in benzene solution. The mechanisms of the photolysis of polystyrene as film and in benzene solution, in vacuo and in the presence of oxygen, are discussed and interpretations proposed. The pronounced yellowing of polystyrene during the photooxidation process is interpreted as a reaction involving benzene ring‐opening photooxidation in polystyrene molecule. These results were obtained by comparing ultraviolet and infrared spectra in experiments of photooxidation of pure liquid benzene and polystyrene film.
Radiation‐induced emulsion polymerization of ethylene. IV. Effect of pressure, temperature, and additives on rate in connection with number of polymer particles
Authors: Senrui Shiro , Takehisa Masaaki
Published: April 2003

The effects of pressure, temperature, and additives on the rate of radiation‐induced emulsion polymerization of ethylene with FC‐143 as emulsifier were studied kinetically. The rate of polymerization was proportional to the 2.5 power of ethylene fugacity, and the apparent rate constant (rate of polymerization/2.5 power of ethylene fugacity) was constant below 78°C. Above this temperature, the rate constant decreased with an apparent activation energy of −8.2 kcal/mole. These facts can be interpreted in connection with the polymer structure and the change of rate of escape of radicals from the polymer structure and the change of rate of escape of radicals from the polymer particle into the aqueous phase. The rate of polymerization decreased on addition of a series of n‐aliphatic alcohols due to the chain‐transfer reaction and consequent escape of radicals to the aqueous phase. On the other hand, the addition of tert‐butyl alcohol increased the rate of polymerization, probably because of its effect in increasing swelling of the polymer particles. Addition of electrolytes increased the rate of polymeriaztion as a result of the increase of the number of polymer particles.