bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular organization of the coupling agent interphase of fiber‐glass reinforced plastics
Authors: Ishida Hatsuo , Koenig Jack L.
Published: April 2003

The structure of the silane coupling agent interphase of fiber‐glass reinforced plastics has been studied by Fourier transform infrared and laser Raman spectroscopy. It is found that there is a degree of order in the molecular organization of the coupling agent interphase for the vinyl and cyclohexyl functional silane coupling agents. When a cyclohexyl functional silane is used, crystalline layers of silanetriol on the glass fibers are observed. The extent of order is determined by the structure of the adsorbed species, which is influenced by the structure of the silane in the treating solution. Two factors introducing disorder in the interphase are the magnitude of aggregation of the silanes in solution and irregularities in the topology of the glass surface.
Transitions and the relaxation spectrograph: Poly(oxymethylene)
Authors: Blumberg Avrom A. , Niemira Edwin R.
Published: April 2003

In place of directly assaying the relative rebound height of a ball from a polymeric sample, the passage time of the ball between fixed points is used in a much more precise version of the poor man's relaxation spectrograph. Poly(oxymethylene) has a sharp transition at — 74.8°C which progressively becomes broader and moves to — 39.0°C as the polymer is pretreated at 70°C and exposed to 330 nm light for times up to 1038 ksec. A second transition, broad and shallow, is seen in the range 104 to 124°C and is unaffected by the pretreatment. This is attended by a slight decrease in density, proportional to the time held at 70°C, at the rate of −3.54 × 10−9 g/cm3 sec.
Dynamic mechanical properties of polymers filled with agglomerated particles
Authors: Nielsen Lawrence E.
Published: April 2003

The filler particles in most filled polymers are not perfectly dispersed but are more or less agglomerated. The degree of agglomeration and the strength of the agglomerates, which can be modified by surface treatments, have a very great effect on the dynamic mechanical properties. Filler agglomerates which are wetted by the polymer matrix produce higher elastic moduli than similar agglomerates which are not wetted. The relative damping in most filled polymers is very temperature‐dependent. A qualitative explanation is given for this temperature dependence. The degree of agglomeration and the strength of the agglomerates are important factors in determining the damping.
Equation of state of semicrystalline and crystalline polymers
Authors: Jain R. K. , Simha Robert
Published: April 2003

The equation of state of a semicrystalline system can be expressed in terms of the corresponding functions for the crystal and the melt, extrapolated into the solid region. This relation may be employed to obtain crystal data by means of information on the semicrystalline material or vice versa. We consider four polymers, namely, polyethylene (LPE), isotactic polypropylene (PP), polyethylene glycol (PEG), and poly(tetrahydrofuran) (PTHF). For LPE, the combination of melt and crystal theories predicts satisfactorily the volume of the semicrystalline polymer at atmospheric and elevated pressures. Good agreement between theory and experiment obtains for PEG and PTHF equilibrium melts. In addition to a PP sample measured and discussed by Zoller, a second PP polymer by Leute et al. is considered. From the corresponding semicrystalline data, the equation of state of the crystal is then derived. The PVT results for the three crystalline polymers obtained in this indirect manner are in satisfactory agreement with the predictions of crystal theory. For purposes of comparison, a polymer melt with a low melting point, viz., cis‐1,4‐polybutadiene, is also discussed in terms of theory. A consideration of the scaling parameters and derived quantities for both crystal and melt had resulted in certain correlations encompassing LPE, PVF2, and PClF3. These cannot be generalized to the systems considered here, particularly in the crystalline state. PEG stands out in respect to several characteristic quantities in both states, whereas PP can be more nearly grouped with the previous three polymers. The theoretical equation of state for the polymer crystal does not satisfy a principle of corresponding states. However, practically useful and accurate interpolation formulas for the theoretical expressions, polynomials at atmospheric pressure, and Tait equations for the compression ratios are derived. Over certain ranges of reduced temperature and pressure, the theoretical isotherms can be approximated by master curves for the four polymers. At atmospheric pressure, such representations are limited.
Polymer solidification as a dissipative process
Authors: Lindenmeyer Paul H.
Published: April 2003

Because their conformational entropy is a nonlinear function of size, polymer molecules can only solidify under conditions far from equilibrium with the formation of dissipative structures. A dissipative structure is nonhomogeneous, it evolves with time from an initially space‐dependent fluctuation, and has a characteristic size that depends upon the initial perturbation and the conditions that apply during its entire history. The glass transition is envisioned as the formation of the ultimate dissipative structure where all of the latent heat of crystallization is dissipated within the structure. The mechanism of glass formation can be described as the spinodal decomposition of a homogeneous liquid into two interpenetrating networks of high‐ and low‐energy solids with a characteristic distance and a gradient of density and/or composition extending through both high‐ and low‐energy regions.
Isobaric thermal behavior of glasses during uniform cooling and heating: Dependence of the characteristic temperatures on the relative contributions of temperature and structure to the rate of recovery. II. A one‐parameter model approach
Authors: Kovacs A. J. , Hutchinson J. M.
Published: April 2003

Isobaric variations of the characteristic temperatures Tg and Tmax, obtained on uniform cooling and heating of glasses, are investigated in terms of their dependence on the relevant experimental variables, using a single retardation time model. The corresponding partial derivatives of Tg and Tmax are derived as functions of the partition parameter x (ranging between zero and unity), which determines the relative contributions of temperature and structure to the retardation time. It is shown that the variation of Tg with the cooling rate is independent of x. In contrast, Tmax critically depends on x, and its value as well as those of its three partial derivatives are linear functions of x−1. The variations of Tmax are analyzed in terms of a set of reduced variables, leading to simple reduction rules between any two of the experimental variables when the third is kept invariant. The reduction rules are further substantiated by investigating the behavior of glasses in two‐step thermal cycles, which result in a unique set of inter‐relationships between any pair of the partial derivatives of Tmax, whatever the value of x. The results are discussed in terms of their relevance to the behavior of real glasses.
Ratios of average molecular weights and molecular weight distributions in polymers
Authors: Pyun C. W.
Published: April 2003

If Mmin and Mmax are lower and upper bounds, respectively, to the molecular weights of different molecular weight species contained in a polymer, the weight‐average to number‐average molecular weight ratio Mw/Mn cannot exceed (1 + Mmax/Mmin)2/(4Mmax/Mmin). The ratio attains this maximum possible value if the masses of the two species with molecular weights Mmin and Mmax are equal and the masses of all the other species are negligibly small, corresponding to maximum spread in the molecular weight distribution within the specified bounds. Also for a given value of Mw/Mn = α, the Mmax cannot be smaller than [2α − 1 + 2α1/2(α − 1)1/2]Mmin. The minimum possible value of Mmax/Mmin consistent with α given is obtained in the case of maximum spread described above. If only one species is predominant, then both Mw/Mn and Mmax/Mmin approach unity, as is well known. Similar relations hold for the ratios of higher‐order average molecular weights for which the role of the mass fractions is replaced by higher‐order distribution functions.
Chain conformations of block copolymers
Authors: Kurata Michio , Kimura Tsunehisa
Published: April 2003

An analytical theory of block copolymer conformations is developed for systematically studying the effects of the chain length, chain architecture, and segment interactions. The main results obtained for AB diblock and ABA triblock chains are as follows: (i) In the absence of AA and BB interactions, both diblock and triblock chains collapse to a dense form if the AB interaction is attractive. In the collapsed coil form, the mean‐square end‐to‐end distance 〈R2〉 is proportional to the square root of the number of segments n1/2. (ii) The diblock chain has a dumbbell form if AA and BB interactions are attractive and AB interaction repulsive, but the triblock chain collapses. In the dumbbell form, 〈R2〉 is proportional to n.
Longitudinal acoustic mode in polymers. V. Nature of perturbing forces in n‐paraffins and polymers
Authors: Chang Chih , Krimm S.
Published: April 2003

Binary mixtures of n‐paraffins have been examined by Raman spectroscopy in order to elucidate the nature of the perturbations on the chains. For a short‐chain species diluted in a longer‐chain species, the longitudinal acoustic mode frequency of the former decreases from its value in the pure state to that corresponding to a chain with free ends. This observation, as well as others, confirms our previous suggestions that longitudinal perturbing forces are responsible for increasing this frequency over its unperturbed value. These results also provide new insights into the structures present in solid solutions of n‐paraffins. They reemphasize the necessity of incorporating the effects of such perturbations in applications of the longitudinal acoustic mode to morphological studies of polymers.
Evaluation of the relaxation modules from the response to a constant rate of strain followed by a constant strain
Authors: Smith Thor L.
Published: April 2003

The stress response σ(t) to a constant rate of strain $ \dot \varepsilon $ ε during the period 0 < t ≤ t* and to the constant strain ε* $ ( = \dot \varepsilon t*) $ thereafter is considered in terms of the Boltzmann superposition principle. When t ≤ t*, the data directly give the constant‐rate modulus F (t) ≡ σ(t)/ε(t), which can be converted straightforwardly into the relaxation modulus E(t). Results from illustrative calculations show that a reduction in the relaxation rate effects a decrease in [σ(t*)/ε*]/E(t*) and also in the time at which [σ(t)/ε*]/E(t) becomes essentially unity. To evaluate E(t) at t > t*, F(t) is first obtained from σ(t) and F(t − t*) by using a derived equation similar to that presented by Meissner. Thereafter, F(t) is transformed into E(t). For illustration, E(t) for a rubbery solid is evaluated over some 2.5 decades of time from its response to a strain rate of 0.25 min−1 for 0.40 min and thereafter to the attained strain of 0.10 for 5.4 min.
Permeability of heterogeneous gels
Authors: Weiss N. , Van Vliet T. , Silberberg A.
Published: April 2003

Gels made by radical copolymerization of monofunctional and difunctional monomer units in the presence of swelling medium will tend to be heterogeneous. A case in point is acrylamide co‐polymerized with N,N′‐methylene bis‐acrylamide in water. Such gels can be assumed to be two‐phasic with both phases gels, but of different average concentration and average degree of cross‐linking. As Weiss and Silberberg have shown, permeability can be used to characterize the distribution in space. In this paper, their earlier model is expanded and improved by considering specifically the permeability of each of the two phases and taking into account that each of these phases separately must have come into swelling equilibrium with the swelling medium, water. It can be shown that only the length of the Kuhn statistical element remains as a free parameter in this model. Essentially the same value of this parameter, however, accurately accounts for the measured permeability. It is found that at an overall volume fraction of about 0.16, the two‐phase structure tends to disappear. For higher degrees of crosslinking, this occurs because the more dilute phase takes over the entire space; for more lightly crosslinked systems, the more concentrated phase takes over. The heterogeneity of the distribution lies in the nanometer range and reasonable agreement between the results obtainable from permeability and from viscoelasticity can be demonstrated. These results are consistent with the model for the polymerization process.
Effect of microroughness on rubber friction
Authors: Borch Jens
Published: April 2003

Friction was measured and analyzed for rubber belts sliding against paper and polymer film surfaces of different roughness. As expected, increased paper smoothness created an increase in the friction coefficient. However, it was found that continuous rubber usage during testing also created an increase in friction coefficient for constant surface roughness of both paper and film. This was analyzed as due to an increase in N and C values for the load‐dependent friction coefficient, μ = CW−N where W is normal load and Nmax ≈ 0.33 (papers) or Nmax ≈ 0.6 (polymer films). Using adhesion friction theory, it was shown that friction data can be fitted with a unified equation: C = μ0c−N, where μ0 = μ N = 0 and c is a constant for the rubber and belt configuration tested.
Correlation between environmental stress cracking and liquid sorption for low‐swelling liquids
Authors: Shanahan M. E. R. , Schultz Jacques
Published: April 2003

The environmental stress cracking (ESC) of polyethylene has been studied under conditions of dynamic equilibrium with the liquid for low‐swelling liquids. Even among active ESC agents, there is a clear relative order of efficiency. It has been shown that the liquid becomes less efficient with increasing equilibrium swelling. This fact has been attributed to local plasticization of the crack front leading, in turn, to a reduction in the high‐stress concentrations associated with a wedge‐shaped crack. Some semiquantitative ideas are proposed in an attempt to explain the relation between ESC efficiency and volume/volume sorption.
Molecular motion and spin relaxation in polydiethylsiloxane
Authors: Burnett L. J. , Durrett M. G.
Published: April 2003

Quantitative comparison of previously published NMR spin‐relaxation data for polydiethylsiloxane with theoretical predictions for a variety of motional processes allowed both the nature and time scale of molecular motions to be identified. At the lowest temperatures, methyl reorientation produced a T1 minimum and was found to proceed with an activation energy of 2.4 kcal/mole in both amorphous and crystalline phases. Reorientation of the ethyl groups in the amorphous phase was observed at a higher temperature with an activation energy of 9.3 kcal/mole. Relaxation in the melting region was influenced by flexing and stretching of the helical polymer chain. The maximum angular displacement of the chain was estimated to be 24°, with an activation energy for this process of 2.6 kcal/mole.
Crystallization of alkyl‐aromatic polyimides (polyalkanimides)
Authors: Korshak V. V. , Babchinitser T. M. , Kazaryan L. G. , Vasilyev V. A. , Genin Ya. V. , Azriel A. Ye. , Vygodsky Ya. S. , Churochkina N. A. , Vinogradova S. V. , Tsvankin D. Ya.
Published: April 2003

Polyalkane imides based on 3,3′,4,4′‐diphenyloxidetetracarboxylic, pyromellitic and 1,4,5,8‐naphthalenetetracaboxylic acids, and aliphatic diamines containing 4, 6, 8, 10, or 12 methylene groups have been studied. Relations governing the effect of structure on solubility, heat resistance, density, and crystallizability have been established. Conformation analysis has been carried out and models of the macromolecules have been constructed. The morphology of the crystalline polymers has been studied. For the polymers of the given class, crystallization capability is shown to be associated with the conformational flexibility of the macromolecular unit determining a given acid moiety by the number of methylene groups in the diamine unit.
Displacement measurements using double‐exposure speckle photography of small‐angle scattered light
Authors: Holoubek J. , Sedláček B.
Published: April 2003

Double‐exposure speckle patterns created by scattered light were used to study tensile deformation of isotactic polypropylene film. The method makes possible a quantitative investigation of the deformation process (relative magnitude and orientation of the displacement vector, Poisson's ratio μ) by means of a simple optical analysis of stepwise deformations covering the desired range. The displacement vector and Poisson's ratio have been determined with an accuuracy of ± 5% in the range of small deformations (up to 18% relative deformation); and the role of stress relaxation has been examined. Limitations of the method, such as the range of measurable displacements, effect of prestressing, and stability of the system, etc., are discussed. Among advantages of the method are comparative simplicity and accuracy, and the possibility of its application to other systems studied by the small‐angle light scattering method.
Birefringence of stretched polyethylene and its relation to changes in structure
Authors: Pietralla M. , Kilian H.‐G.
Published: April 2003

It is shown that the birefringence of a polyethylene crystal can be severely shape dependent via the internal field. Using the cluster model it is concluded that this dependence plays an important role in the structural transition in the uniaxial stretching process.
Effect of casting conditions on polymorphism of nylon‐12
Authors: Ishikawa Toshihiko , Nagai Susumu , Kasai Nobutami
Published: April 2003

Polymorphism in nylon‐12 film, which appears on casting from a phenol‐ethanol solution, has been investigated by x‐ray diffraction and infrared absorption. The casting temperature was varied from 30 to 130°C and the ambient atmospheric pressure from 50 to 760 Torr. Casting at 30°C gives only the α form, while casting above 90°C yields only the γ form. At intermediate temperatures, both α and γ forms are obtained, with the γ content increasing as the casting temperature and/or the rate of evaporation of solvent are increased. The ethanol component of the casting solvent appears to act only as a melting‐point depressant for phenol. In contrast, nylon‐6 film cast from the same solvent system between 30 and 160°C gives only the α form. It is proposed that the difference in polymorphism of nylons‐12 and ‐6 is caused by differences in molecular flexibility due to the length of the methylene chain.
Structural investigations of polymer liquid‐crystalline solutions: Aromatic polyamides, hydroxy propyl cellulose, and poly(γ‐benzyl‐L‐glutamate)
Authors: Onogi Yoshihiko , White James L. , Fellers John F.
Published: April 2003

A comparative structural investigation of the characteristics of polymer liquid‐crystalline solutions including Kevlar® (PPD‐T)/sulfuric acid, poly(Cl‐p‐phenylene terephthalamide) (Cl‐PPD‐T)/sulfuric acid, poly(γ‐benzyl‐L‐glutamate) (PγBLG)/dioxane, and hydroxypropyl cellulose (HPC)/water was undertaken. Experimental procedures included polarized light microscopy, light scattering, absorption spectra, and x‐ray diffraction on solutions at various concentrations and temperatures. Both the two‐phase region at the onset of liquid‐crystal formation and the wholly anisotropic phase were investigated. Each solution exhibited distinctive characteristics. The PPD‐T and Cl‐PPD‐T solutions were nematic, and the PγBLG and HPC solutions were cholesteric. In the two‐phase region the PPD‐T, Cl‐PPD‐T, and PγBLG (but apparently not the HPC) exhibited negatively birefringent spherulites and aggregates of spherulites. The HPC solutions only exhibited spherulitic structures in the single‐phase anisotropic system. The structures and orientations in the anisotropic phase for the various polymer solutions is considered. The helicoidal structural characteristics of the PγBLG and HPC solutions are contrasted.
Crystal structure of polyamides containing 1,3‐cyclohexane rings
Authors: Inoue Kazuo , Hoshino Sadao
Published: April 2003

The effect of 1,3‐cyclohexane rings in the chain backbone on the crystal structure of polyamides has been studied using polyamides (denoted 1,3‐CBMA‐n) obtained from 1,3‐cyclohexane‐bis(methylamine) (1,3‐CBMA) and n‐carbon dicarboxylic acids. The crystallinity of the 1,3‐CBMA‐n polymers changes greatly with variation in the value of n. This is attributed to hydrogen‐bond changes associated with the relative length of the diacid moiety to the diamine moiety in the monomeric unit of each polymer. In 1,3‐CBMA‐6, the cis‐1,3‐cyclohexane rings are readily accommodated in the molecular chains to form crystals in a manner similar to the m‐benzene rings in poly(m‐xylylene adipamide) (MXD‐6). The crystal lattice, however, is more expanded than in MXD‐6 since the 1,3‐cyclohexane rings is bulkier than the m‐benzene ring. The crystal structure of the 1,3‐CBMA‐n polymers is essentially the same as that of MXD‐6.
Effect of moisture on the bulk properties of salted poly(caproamide)
Authors: Acierno D. , La Mantia F. P. , Titomanlio G. , Ciferri A.
Published: April 2003

The glass‐transition temperature (Tg) and the elastic modulus of nylon‐6 and its mixtures with 4% w/w LiCl and with 2% LiCl+3% LiBr were investigated. In one set of experiments care was taken to avoid absorption of moisture during the measurements. In another set of experiments, samples were exposed to atmospheric humidity for different lengths of time. Both unoriented and oriented specimens were investigated. The presence of 4% LiCl almost doubles the amount of moisture absorbed at equilibrium by nylon‐6. The Tg was found to be greatly affected by the moisture content and by salt type. When strict precautions to exclude moisture are taken, the addition of 4% LiCl raises the Tg of nylon‐6 by about 25°C. The elastic modulus of oriented samples is increased by the addition of salts provided moisture is completely absent. This beneficial effect is, however, completely eliminated when samples are allowed to equilibrate with atmospheric moisture.
Morphology and tensile property relations of high‐strength/high‐modulus polyethylene fiber
Authors: Wu W. , Simpson P. G. , Black W. B.
Published: April 2003

High‐strength/high‐modulus polyethylene (PE) fibers have been obtained from linear polymers by melt‐spinning the polyethylene followed by hot‐drawing the spun filaments. Fibers with different tensile properties were made by changing the extrusion, solidification, and drawing conditions and by use of different types of polyethylene. Potential correlations of fiber strength with morphological parameters such as crystallite dimensions, and crystalline and amorphous orientation were examined. The integrated meridional small‐angle x‐ray scattering intensity is the only morphological parameter which was found to correlate well with the strength of fibers prepared under different conditions and from different polymer types. Implications with respect to the molecular mechanism of PE fiber drawing are also discussed.
Physical and rheological characterization of poly(aryloxyphosphazene) copolymers
Authors: Futamura S. , Valaitis J. K. , Lucas K. R. , Fieldhouse J. W. , Cheng T. C. , Tate D. P.
Published: April 2003

A series of poly(aryloxyphosphazene)s was prepared with phenoxy and p‐ethylphenoxy substituents in various ratios. The thermal, morphological, and rheological properties of this series of polymers were studied by differential thermal analysis, x‐ray analysis, and rheometrics mechanical spectroscopy. Thermal analysis showed that the resulting polymers follow melting‐point‐depression‐ and glass‐transition‐temperature‐composition relationships expected of random copolymers. The lower first‐order transition temperature [T(1)] disappears near equimolar substitution while the higher first‐order transition temperature (Tm) persists over the whole range of compositions. X‐ray analysis revealed that crystalline order in the polymer chain direction is destroyed by nearly equimolar substitution but lateral order remains. The rheological characterization of a copolymer with nearly equimolar substitution showed that the polymer is in a pseudocrosslinked state indicating the existence of chain‐to‐chain interactions. When a small amount of an antioxidant (6‐dodecyl‐1,2‐dihydro‐2,2,4‐trimethylquinoline) is added, the lateral order of the copolymer is destroyed, and its rubbery plateau modulus decreases by several fold.
Intrinsic viscosity of flexible ring polymers
Authors: Alessandrini J. L.
Published: April 2003

The intrinsic viscosity of flexible ring polymers with a finite number of segments is computed with both exact and approximate eigenvalues λk, in the frame of the elastic necklace model. It is shown that exact and approximate calculations of the Flory constant and the Kuhn‐Mark‐Houwink exponent of the non‐free‐draining limit are compatible with h* ⋍ 0.25 and N ≥ 100.
Measurement of single chain neutron scattering in concentrated polymer solutions
Authors: Akcasu A. Z. , Summerfield G. C. , Jahshan S. N. , Han Charles C. , Kim Chung Yup , Yu Hyuk
Published: April 2003

For some time there have been measurements of single‐chain form factors for small‐angle neutron scattering (SANS) in bulk polymers and in concentrated solutions. These were done by mixing a fraction of completely deuterated polymer with the normal polymer. Until recently, it was believed that these experiments had to be performed using a small fraction of deuterated polymer to avoid interchain interference effects. However, the work of Williams et al. has shown that these experiments are better if one uses large fractions of marked polymer and determines both the single chain and interference contributions to the SANS cross section. We generalize the technique of Williams et al. somewhat and apply it to the measurement of the radius of gyration of polyisoprene in the bulk.
Observation of bands in high‐modulus aramid fibers by polarization microscopy
Authors: Simmens S. C. , Hearle J. W. S.
Published: April 2003

Examination of the highly oriented aramid fiber, Kevlar, at high magnification in an optical microscope in the extinction position between crossed polars gives an image with regions of regular fine bands. The diffraction pattern shows first order but no zero order. This is interpreted as being due to the passage of depolarized scattered light from a material with regularly spaced discontinuities. This is identified with the pleated structure proposed by Dobb et al.
Model for sorption of mixed gases in glassy polymers
Authors: Koros W. J.
Published: April 2003

A model is presented for analysis of the sorption of mixed gases in glassy polymers at concentrations below which significant plasticization occurs. The well‐known dual‐mode sorption model comprised of a Henry's law term and a Langmuir isotherm term, which has been used extensively for interpretation of single‐component gas sorption data, forms the basis for the analysis of binary mixtures discussed here. Measurements using pure gases provide dual mode parameters which can then be used to predict the resultant sorption isotherms for binary mixtures of any of the pure gases. The proposed analysis is based upon recognition that the Langmuir component of the overall sorption concentration should be governed by competition between the two penetrants for the fixed unrelaxed volume in the polymer, which is believed to be the locus of the Langmuir capacity. This effect may result in a significant depression of the measured sorption of similar penetrants competing for the limited Langmuir capacity. A numerical example is considered which illustrates the range of behavior expected for CO2 and CH4 in polycarbonate. Deviations from the theoretical predictions of the simple dual‐mode model for binary systems are discussed in terms of plasticizing effects on the Henry's law constant and the Langmuir affinity constant. The analyses proposed here are of direct and critical interest to the applied problems of migration of trace contaminants in glassy polymers and analysis of barrier packaging for foods since all of these applied problems involve mixed‐penetrant sorption. Specifically, it is predicted that the presence of residual monomers or solvents in glassy polymers can produce both anomolously low Langmuir sorption affinity constants and sorption enthalpies compared with the residual‐free case.
Structure of glassy polymers. VII. Small‐angle X‐ray scattering from epoxy resins
Authors: Matyi R. J. , Uhlmann D. R. , Koutsky J. A.
Published: April 2003

The small‐angle x‐ray scattering (SAXS) from an Epon 812 and two Epon 828 (one amine‐cured and one anhydride‐cured) epoxy resins has been measured using a Bonse‐Hart system. The data cover the angular range (2θ) between 20 sec and 60 min. After correction for absorption, background and vertical beam divergence, they have been placed on an absolute basis by comparison with the scattering from a previously studied polycarbonate sample. The corrected absolute intensity decreases strongly with increasing angle between 20 sec and 2 min, decreases more gradually between 2 and 20–30 min, and reaches a nearly constant asymptotic value at larger angles. The magnitude of the intensity in the constant‐intensity region is close to the value predicted by thermodynamic fluctuation theory for fluids applied at the glass transition temperature. The increase in intensity at angles smaller than 20–30 min is associated with heterogeneities in the cured resins. These heterogeneities cover a range of sizes in all samples, from less than 100 Å to more than 1000 Å, with the most frequently occurring size in the range 100–200 Å.
Crystal orientation relaxation studies of polyethylene
Authors: Cembrola Robert J. , Stein Richard S.
Published: April 2003

Wide‐angle x‐ray relaxation studies were performed on films of low‐ and high‐density polyethylene (PE). The samples were rapidly stretched by a pneumatic stretcher and held at a fixed length. The rate of crystal reorientation was monitored by measuring diffracted intensity changes using a count‐rate meter with output displayed on a storage oscilloscope as well as a digital counter‐timer. Experiments were completed at several temperatures and activation energies comparable to those reported for the α1 relaxation in PE were obtained.
Kinetics of the II‐III phase transformation of polytetrafluoroethylene at high pressure
Authors: Nicol Malcolm F. , Wiget Joseph M. , Wu C. K.
Published: April 2003

The rate of transformation from helical to all‐trans‐planar polytetrafluoroethylene (PTFE) at high pressures has been determined by monitoring the Raman spectra of PTFE following pressure jumps from the stability field of PTFE II to pressures between 9 and 14 kbar at temperatures between 0 and −30°C. The transformation kinetics can be described by Avrami's equation for nucleation and growth kinetics with an exponent of 0.5, although observations at lower temperatures suggest that even smaller values of the exponent may be appropriate. At 10 kbar and 0°C, the specific rate constant is 0.51 min−1/2. The energy and volume of activation are 11 kcal mole−1 and −7 cm3 mole−1, respectively. The values of these parameters suggest that the transformation mechanism involves propagation of helix reversal planes along the several adjacent chains leaving all‐trans material in their wakes.
Distribution of chain defects and microstructures of melt crystallized polyethylene. II. Influence of defect size and of plastic deformation
Authors: Baltá‐Calleja F. J. , Hosemann R.
Published: April 2003

Unit cell expansion data for (a) melt‐crystallized polyethylene (PE) containing known amounts of methyl, ethyl, and butyl branches and for (b) plastically deformed samples, are examined in the light of a model which takes into account the penetration of constitutional defects (branches) at interstitial crystal sites by means of a generation of 2g1 step chain defects (kink isomers). The present analysis complements previous results obtained for melt‐crystallized PE samples with a widely varying number concentration ϵ of butyl or longer branches. An estimation of the concentration of chain defects incorporated into the crystal lattice is carried out. The results reveal that the fraction χc of defects which are accomodated within the lattice depends on both the amount and size of the chain defects and on the mechanical deformation of the sample. For PE chains with methyl and ethyl groups, χc ≈ 50%, whereas for butyl and longer branches, χc does not exceed 20% of the total concentration of defects. In addition, after cold drawing, PE with low amounts (ϵ < 1%) of butyl or longer chain branching, χc turns out to be zero; i.e., during deformation single molecular chain rearrangements leading to a chain segregation of defects into the amorphous phase must occur.
Dependence of the conformational parameters of polyimides on the chemical structure of the chain
Authors: Pavlova S.‐S. A. , Timofeeva G. I. , Ronova I. A.
Published: April 2003

The flexibility of some polyimide chains has been studied theoretically as a function of the chemical structure of the repeat unit. It has been shown that the thermodynamic flexibility can be varied over a wide range by the choice of the unit structure. For three polyimides, as an example, the flexibility of cyclochain structures approximates that for free rotation.
Thermal conductivity of oriented crystalline polymers
Authors: Choy C. L. , Chen F. C. , Luk W. H.
Published: April 2003

Thermal conductivities of six oriented semicrystalline polymers which range from 0.37 to 0.63 in crystallinity and 1 to 5 in draw ratio λ (up to about 15 for two polymers) have been measured between 100 and 340 K. It was found that for increasing λ the conductivity K∥ (along the draw direction n̂) increases rapidly while K⊥ (normal to n̂) decreases slightly; K∥ also increases with temperature, but K⊥ shows no simple pattern in temperature dependence. These general features can be reproduced reasonably well at low draw ratio (λ < 5) by the modified Maxwell model, and the discrepancy in details may be attributed to the fact that the model does not take into account the possible anisotropy of the amorphous phase of the oriented polymers. At high draw ratio the intercrystalline bridge effect becomes important, and one must resort to the Takayanagi model, but the lack of corroborating x‐ray data has rendered a detailed comparison impossible.
Single crystals of cellulose IVII: Preparation and properties
Authors: Buleon A. , Chanzy H.
Published: April 2003

Lamellar single crystals of cellulose were obtained from dilute solutions of low‐DP cellulose triacetate, by deacetylation followed by precipitation. At temperatures between 150 and 160°C, pure cellulose IVII crystals were obtained whereas at temperatures between 90 and 150°C, hybrid crystals, having cellulose II and cellulose IVII domains cocrystallized in syntaxy were obtained. In both cases, the crystals were identified and characterized by electron diffraction. When the solutions leading to cellulose IVII were seeded with native cellulose microfibrils, a shish‐kebab structure resulted with the microfibrils decorated by cellulose II lamellae.
Polymer diffusion at intermediate concentrations
Authors: Chitrangad B. , Osmers H. R.
Published: April 2003

Schlieren optics in conjunction with a modified Claesson cell allows free‐diffusion experiments to be performed over a wide range of polymer concentrations. A data analysis procedure is presented for computation of the mutual diffusion coefficient using this technique. The dependence of the diffusion coefficient on concentration in polymer solutions is satisfactorily explained in terms of free volume, and a relation is proposed for correlating the mutual diffusion coefficient and zero‐shear viscosity.
High‐temperature morphological transition in a styrene‐butadiene‐styrene block copolymer
Authors: Chung C. I. , Griesbach H. L. , Young L.
Published: April 2003

Electron microscopy reveals a high‐temperature morphological transition in a styrene‐butadiene‐styrene block copolymer of 7000 polystyrene block molecular weight and 43,000 polybutadiene block molecular weight (7S‐43B‐7S). Samples quenched in liquid nitrogen from temperatures above 150°C show no structure, whereas those quenched from temperatures below 140°C clearly show a multiphase structure. We previously reported that the 7S‐43B‐7S polymer exhibits a relatively sharp melt rheological transition in the temperature region between 140 and 150°C from highly viscoelastic and nonlinear viscous behavior to linear viscous behavior with insignificant elasticity. The dynamic viscoelastic properties are measured at different strain amplitudes in this study, and the results show that the melt rheological transition behavior is not influenced by the strain amplitude. This study clearly shows that the melt rheological transition in the 7S‐43B‐7S results from a morphological transition from a multiphase structure below about 140°C to a single‐phase structure above about 150°C.
Morphology and melting behavior of semicrystalline poly(ethylene terephthalate). I. Isothermally crystallized PET
Authors: Groeninckx G. , Reynaers H. , Berghmans H. , Smets G.
Published: April 2003

A detailed description of the morphology and the complex melting behavior of poly(ethylene terephthalate) crystallized isothermally in the range 100–245°C is presented. Double or single melting endotherms can deliberately be obtained by varying the heating rate in the differential scanning calorimeter (DSC). In the case of double melting peaks, the first endotherm (I) corresponds to the melting of the crystalline material formed at the crystallization temperature Tc. The second melting endotherm (II) originates from the melting of a fraction of the original crystalline material reorganized during the DSC scan. The appearance of one melting endotherm (I or II) relates to the melting of the original structure or the melting of a completely transformed structure. Taking the end of the melting endotherm I as the final melting temperature TM of the material, an equilibrium melting temperature of 290°C is obtained from a plot of TM vs. Tc. A detailed morphological study of the isothermally crystallized samples by electron microscopy and both small‐angle and wide‐angle x‐ray scattering raises questions about the use of the two‐phase concept in relating morphological parameters and melting behavior at low crystallization temperatures.
Direct evaluation of the electron density correlation function of partially crystalline polymers
Authors: Strobl G. R. , Schneider M.
Published: April 2003

A discussion of the general properties of the one‐dimensional electron density correlation function K(z) of a partially crystalline polymer with lamellar structure shows that application of a graphical extrapolation procedure permits direct determination of the crystallinity, the specific inner surface, and the electron density difference ηc − ηa. The procedure is based upon the occurrence of a straight section in the “self‐correlation” range of K(z). Curved and nonparallel lamellae do not invalidate the concept. In the case of heterogeneous samples composed of partially crystalline and totally amorphous regions, some of the parameters of the experimentally obtained correlation function, as for example the invariant K(0), are affected and may lose their definiteness. Use of the method is demonstrated in a detailed discussion of the correlation functions measured for a sample of lowdensity polyethylene at 25 and 100°C.
Model of partial crystallization and melting derived from small‐angle X‐ray scattering and electron microscopic studies on low‐density polyethylene
Authors: Strobl G. R. , Schneider M. J. , Voigt‐Martin I. G.
Published: April 2003

A temperature‐dependent small‐angle x‐ray scattering and electron microscopic study on a sample of low‐density polyethylene affords a determination of the structure changes in a heating and cooling cycle and suggests a new model of partial crystallization and melting. The analysis of SAXS data is based upon some general properties of the electron‐density correlation function. Electron micrographs are obtained from stained sections γ irradiated at elevated temperatures and are analyzed quantitatively by statistical means. According to the model proposed here the thickness distribution in the amorphous layers, rather than that of the crystalline regions, is the essential factor governing the crystallization and melting behavior. The temperature‐dependent changes in this thickness distribution provide a natural explanation for the large reversible changes in long‐spacing.
Thermochromism in polydiacetylene solutions
Authors: Patel G. N. , Witt J. D. , Khanna Y. P.
Published: April 2003

A novel planar ↔ nonplanar visual thermochromic conformational transition of polydiacetylene molecules in poor solvents is reported. The conformational transition is associated with both a color change (blue or red ↔ yellow) and a change in the state; the yellow solution (liquid) transforms to a blue or red gel (solid). The color transition occurs within a narrow range of temperature and has a large associated hysteresis. The enthalpy of the conformational transition is 29 kJ/mole of repeat unit. Fourier‐transform infrared studies show that molecules acquire a planar conformation in red or blue gels by formation of intramolecular H bonds between the adjacent substituent groups. Virtually all H bonds break (a nonplanar conformation) when the gels turn into yellow solutions.
Thermal behavior of α nylon‐12
Authors: Ishikawa Toshihiko , Nagai Susumu , Kasai Nobutami
Published: April 2003

The thermal behavior of α nylon‐12 film cast from a phenol‐ethanol mixture has been studied by differential scanning calorimetry. Polymorphism has been analyzed by x‐ray diffraction. The γ form exhibits a single endothermic melting peak in the thermogram, whereas the α form exhibits double peaks. Samples with mixed α and γ forms show double peaks at the same positions and the area ratio changes in accordance with the amounts of the two forms. The appearance of the γ peak, even for the α sample, is explained by recrystallization to the γ form after melting of the α form. The melting point of α nylon‐12 is ca. 173°C, which is lower by 6–7° than that of the γ form. Once the α or γ sample has been melted and then cooled, its heating thermogram shows a small peak before the appearance of the main peak. The small peak seems to be due to incomplete and/or smaller crystallites formed during cooling. Heat treatment below the melting point of α nylon‐12 is effective in transforming the α form to the γ form, probably via a melt‐recrystallization process.
Structure of polyethylene solid solutions from vibrational spectroscopy and thermal analysis
Authors: Shu P. H. C. , Burchell D. J. , Hsu S. L.
Published: April 2003

Solid solutions of two low‐molecular‐weight polyethylene fractions, formed by rapid quenching from the melt, were studied by differential scanning calorimetry, low‐frequency Raman spectroscopy, and Fourier‐transform infrared spectroscopy. Two kinds of defects exist in these solid solutions; namely, a disruption of chain extension and the presence of monoclinic packing. The distribution of fully extended chain‐segment lengths and the intensity of the 717 cm−1 infrared band, characteristic of the monoclinic phase, are found to be composition dependent. Our spectroscopic studies of the solid solutions support the model first proposed by Ott and Slagle.
Dilute solution and rheological characterization of branched poly(2,2′‐oxydiethylene trans‐1,4‐cyclohexanedicarboxylate)
Authors: Fisher L. W. , Pearson G. H. , Yacobucci P. D.
Published: April 2003

The addition of small amounts of polyfunctional agents can substantially alter the melt and the solid‐state properties of polymers. A practical characterization scheme is necessary for control of polymer preparation and for process analysis. Trifunctionally branched samples of poly(2,2′‐oxydiethylene trans‐1,4‐cyclohexanedicarboxylate) have been prepared as representative of polycondensation polymers. The Drott‐Mendelson procedure was applied to the dilute solution data from gel permeation chromatography and intrinsic viscosity to yield the true molecular weight distributions and the average branching frequency. The melt zero‐shear‐rate viscosity of a branched sample was less than that of a linear sample of equal weight‐average molecular weight, in good agreement with Bueche's theory. The melt elasticity, as measured by the terminal relaxation time, was equal to that of the equivalent linear polymer at constant weight‐average molecular weight.
Small‐angle x‐ray scattering study of ionomer deformation
Authors: Roche E. J. , Stein R. S. , Russell T. P. , Macknight W. J.
Published: April 2003

The small‐angle x‐ray scattering (SAXS) pattern from a cesium salt of a 6.1 mole % ethylenemethacrylic acid (E‐MAA) copolymer is shown to become azimuthally dependent on sample elongation. SAXS was measured using the Oak Ridge National Laboratory (ORNL) spectrometer with pinhole collimation and a two‐dimensional position‐sensitive detector. The sample was quenched prior to deformation to avoid crystallization of the ethylene unit which would complicate the interpretation of scattering. The observed SAXS patterns are interpreted in terms of several proposed models for the structure of ionomers. A model in which ionic aggregates are arranged on a paracrystalline lattice is found to be largely in disagreement with the results for undeformed and deformed samples. Spherical and lamellar models incorporating local structure around a central ionic core are capable of predicting the observed SAXS for the undeformed sample. A model of ellipsoidal deformation of the spherical shell‐core model fails to predict the correct azimuthal dependence of scattering. However, a deformation scheme involving rotation of the lamellar model is more satisfactory.
Use of electron microscopy to obtain quantitative information about the melting behavior of branched polyethylene
Authors: Voigt‐Martin I. G.
Published: April 2003

The melting behavior of low‐density polyethylene was studied by electron microscopy. The experimental techniques and method of evaluation chosen were such as to deliver quantitative numerical data. The values which could be derived from suitably prepared histograms were the minimum, maximum, average, and most probable values of the crystal thickness d and long‐spacing L. All these values were in good agreement with small‐angle x‐ray scattering results. The histograms also show the distribution functions for d and L, so that effects leading to changes in the average values can be observed in detail. The results provide further support for a model of melting and crystallization proposed in a previous paper.