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Previous studies have evaluated low molecular weight crystalline materials as latent heat sinks for passive thermal protection systems. This study evaluated crystalline polymers as heat storage materials. Differential scanning calorimetry and Instron thermomechanical analysis are applied in dynamic studies of cumulative histories of melting and recrystallization. Commercially available crystalline polymers with melting temperatures Tm ≥ 100°C can provide fully reversible heats of fusion ΔHm ≥ 35 cal/gm under programmed heating-cooling cycles. A linear polyethylene (Marlex 6050) is modified by radiation crosslinking to retain shape stability above Tm with-out loss of heat storage capability. The essentially zero vapor pressure and inherent shape stability of crosslinked crystalline polymers may provide unique advantages as uncontained, non-expendable, heat storage materials.

Recent work is presented on the plastic deformation of linear polyethylenes. This work demonstrates the importance of molecular weight and initial morphology in determining the drawing behavior, and shows that by appropriate choice of these two factors a substantial increase in draw ratio and hence stiffness can be achieved over conventionally-oriented polyethylenes. Under optimum conditions a modulus of approximately 700 Kbar was obtained at a draw ratio of ∼30. These very high modulus materials displayed an extensibility to break of at least 3 percent and a strength of about 4 Kbar. In some cases they also exhibited very high melting points (∼139°C) and exceptionally good thermal stability.

Different single crystal preparations of polyethylene with (unfractionated) and without (partially fractionated) low molecular weight chains were irradiated at room temperature. G(crosslink) was determined from the gel point. It is shown that in addition to the molecular weight and molecular weight distribution of polymers, G(crosslink) is determined by three more parameters: thickness of crystalline core, amount of amorphous surface layer, and degree of interlamellar contact. Unlike unfractionated polyethylene, partially fractionated polyethylene showed almost 100% gel at about 250 Mrad. To obtain the same amount of gel, unfractionated polyethylene required a much higher dose than that required by partially fractionated polyethylene. Molecular weight distribution of sol fractions of unfractionated and partially fractionated polyethylene was studied by gel permeation chromatography (GPC) and the solubility data analyzed by Charlesby–Pinner plots. It has been shown that the unattainability of 100% gel from unfractionated polyethylene is due to segregation of low molecular weight chains during crystallization which need very high doses for complete gelation.

Crystallization and melting behavior of linear polyethylene under high pressures up to 6000 kg/cm2 has been investigated with a high-pressure dilatometer. Crystallization was carried out at a cooling rate of 1°C/min from the melt at each pressure. The samples were characterized by differential scanning calorimetry, density, and electron microscopy. Folded-chain crystals are formed in the low-pressure region below 2000 kg/cm2. Crystallization in the intermediate-pressure region between 2000 and 3500 kg/cm2 gives a mixture of folded-chain and extended-chain crystals. The extendedchain crystals are the more stable and predominate at increasing pressure. At high pressures above 4700 kg/cm2, two stages of crystallization and of melting can be observed. The phenomenon suggests that the two kinds of extended-chain crystals with different thermal stability, i.e., the ordinary extended-chain crystals and “highly extended-chain” crystals form through individual crystallization processes from the melt at high pressure.

To describe the characteristic crystalline structure of polyolefins, Pennings first proposed a model consisting of a combination of an extended chain crystal (a “shish”) and folded chain crystals (“kebabs”). In Pennings' model the “shish” forms first during a crystallization process under stress and then later the “kebabs” overgrow this “shish” structure epitaxially. Because we had some doubts about such a mechanism, we undertook a series of experimental studies on linear polyethylene, particularly in regard to the crystallization process from a solution under shear. Our conclusion is that the crystals grow first by a screw dislocation mechanism, like whiskers, and then later these are deformed by the shear stress to form the shish kebab structures.

The change of long spacing in polyethylene and nylon-6 during heating at 18°C/min. was measured with an apparatus devised for rapid measurement of the small-angle x-ray diffraction. The apparatus made it possible to obtain a diffraction profile in 1.8 sec. Long spacings increased notably at high temperatures near the melting point, as has been observed during low-rate heating. However, the increase in long spacing during heating was very small in a methoxymethylated nylon-6 sample. This suggests that the increase in the long spacing at high temperature is due to the thickening of crystals. The long spacing in polyethylene samples in the vicinity of the melting point is apparently independent of thermal history.

The effect of molecular weight on the cold drawing behaviour of melt crystallized linear polyethylene has been studied. It is shown that the draw ratio achieved under comparable conditions rises with decreasing M w , very high draw ratios (∼36) being possible for optimum morphology of the undrawn polymer. The yield behaviour was also examined, and it is shown that the yield stress is affected in a complex fashion by both crystallization conditions and molecular weight. These results are discussed in terms of the crystallization and morphology of the melt crystallized polymer.

Freeze-dried chain folded single crystals and the single crystals without amorphous surface layers (crystalline cores) of different thicknesses of linear polyethylene were irradiated with 60Co γ-rays up to 600 Mrad. Concentration of trans-vinylene double bonds and conjugated diene produced during irradiation of the crystals was measured by infrared. Concentrations of trans- vinylene and of the conjugated diene were independent of thickness of crystalline core which suggest that the double bonds were randomly distributed in the crystalline parts of the crystals. Concentrations of trans-vinylene and of conjugated double bonds were lower in chain-folded crystals than in the crystalline cores and this suggests that the folds (amorphous surface layers) are less preferential sites for formation of the double bonds. The zero-order growth and first-order decay kinetics of trans-vinylene double bonds was studied by the equation derived by Dole et al. The equation is strictly obeyed up to 300 Mrad and the results then deviate. Since there is the decay of trans-vinylene double bonds and though there are no crosslinks in the crystalline cores, it has been suggested that the decay of the double bond does not result in the crosslinks.

Extrudates of solid linear polyethylene prepared under proper pressure and temperature conditions have a high c axis orientation along the extrusion direction, with lamellar crystals and amorphous layers stacked alternately along the extrusion direction. Kink bands were formed by compressing the oriented extrudate at room temperature along the extrusion direction. Inspection of the kink bands by wide-angle and small-angle x-ray diffraction and electron microscopy revealed that the fiber axis was rotated from the original axis direction by 70–75° and that the lamellar crystals were inclined to the fiber axis in the kink band by 55–60° and stacked nearly parallel to the kink boundary. The superstructural change during the formation of the kink band could not be interpreted in terms of uniform c axis shear alone. In addition to such a mechanism, it was necessary to take into account intermicrofibril and/or intercrystallite slip.

An experimental method initiated by Williamson and Busse has been extended to produce veil-free shish kebab structures in linear polyethylene without need for severe recovery treatments. The technique involves the dilution of polymer in a concentrated solution of low molecular weight paraffin followed by a simple isothermal shear. The resulting shish kebab structures are isolated from the wax matrix and subjected to electron microscopical and electron diffraction study. From the diffraction patterns, it is shown that the shish-rich ordered structure is similar to the orthorhombic structure of crystalline linear polyethylene, but with certain significant deviations. The resolvable morphology of the shish appears to be characterized by a length-to-diameter ratio which is consistent with a prediction based upon Wulff's theorem utilizing certain relevant surface energy values which have been obtained by others for polymeric crystals.

New experiments are presented which demonstrate the presence of tie-molecules in bulk-crystallized linear polyethylene. The experiments involve analysis by differential scanning calorimetry (DSC) on originally crystallized samples and undissolved residues left behind after partial extraction of these samples. Neue Experimente, welche Tie-Molekule in schmelzkristallisiertem linearem Polyathylen aufzeigen, werden beschrieben. Die Experimente werden mit Differentialthermoanalyse (DSC) an direkt kristallisierten Proben und an ubriggebliebenen, nicht gelosten Ruckstanden nach teilweiser Extraktion dieser Proben durchgefuhrt.

The annealing behaviour and thermodynamics of fusion of mats of solution-grown single crystals of ethylene-propylene and ethylene/1-butene crystallizable random copolymers are examined in comparison with linear polyethylene crystallized from the melt and from dilute solution. Correlation of quantities such as long spacing, annealing temperature, and apparent enthalpy of fusion, leads to the conclusion that the single crystal aggregates are involved in a morphological transformation during the process of annealing. The long spacing and the annealing temperature corresponding to this transformation decrease with the degree of constitutional defects present in the polyethylenic chain (percentage of propylene or 1-butene comonomeric units). Data in the plots of melting temperatures versus the reciprocal of the long spacing can be represented by straight lines. The thermodynamic equilibrium melting temperature T°m and the surface free energy σe have been determined. Both T°m and σe depend upon the number of constitutional defects in the chain. In the case of ethylene-propylene random copolymers σe increases drastically with the percentage of CH3 side groups. A completely opposite effect is observed in the case of ethylene/1-butene random copolymers; here decrease in σe with the percentage of CH3CH2 side groups is observed. Both classes of polymers show a lowering in T°m with the number of side groups, though this effect is much more pronounced in the ethylene-propylene copolymers. The apparent enthalpy of fusion of annealed single crystal aggregates is not in linear relation with the reciprocal of the long spacing and with the corresponding melting temperature. Some consideration on the distribution of the defects in the crystals is also reported.

A study was made by differential thermal analysis (DTA) of the effect of pressure up to 8000 kg/cm 2 on melting and crystallization of linear polyethylene (PE). It was shown that thermograms of melting and crystallization at pressures of over 4000 kg/cm 2 are characterized by the presence of two peaks. The existence of two peaks is a general phenomenon for isotropic and oriented specimens, single crystals and specimens containing crystals with straightened chains. An X-ray study shows that c -axial orientation of elongated specimens during annealing at a pressure of 7000 kg/cm 2 only disappears after the second endothermic peak, i.e. this peak corresponds to the final melting point. The presence of a low temperature peak points to the existence of an intermediate high pressure phase. A phase diagram was plotted under high pressure using DTA results, for isotropic and oriented PE samples up to 8000 kg/cm 2 . A study was made of the effect of the degree of elongation on melting PE under a pressure of 7000 kg/cm 2 .

Crystallization rates, from the melts of linear polyethylene and ethylene—butadiene copolymers, have been measured by differential thermal analysis. The effect of the intra-chain double bonds on the crystallization is discussed. The results are analysed in terms of the Avrami equation. Analysis of the dependence of the rate of crystallization on the undercooling shows that the growth of the spherulites is controlled by a process of surface secondary coherent nucleation. The free energy of formation of a nucleus of critical dimensions depend upon the number of trans double bonds in the polymer chain.

Linear polyethylene crystals have been degraded with oxygen in the presence of a catalyst composed of cobaltous and bromide ions at temperatures between 60 and 130°. The number of carbonyl groups introduced into polyethylene increases as the oxidation temperature is raised. Infra-red spectroscopy and molecular weight evidence suggests that ketone groups are formed by a non-chain scission reaction, whereas aldehyde and carboxylic acid groups result from chain scission reactions. Molecular weight distributions of the degradation products show that reactions occur selectively in the amorphous regions at the crystal surfaces, when oxidations are performed below 110°. At higher temperatures, the chains are degraded randomly. The carbonyl groups introduced into polyethylene were oxidized to carboxylic acid groups with concentrated (∼ 70 per cent) nitric acid. The results demonstrate that this two-stage process yields a polydisperse long-chain linear paraffin with carboxylic acid end-groups, when the catalytic oxidations are performed between 115 and 130°.

An attempt has been made to determine what influence chain folds may have on the α and γ mechanical loss peaks in linear polyethylene. In so doing, one long-chain n-paraffin (C94H190) and two low molecular weight polyethylene fractions have been examined with mechanical relaxation, differential scanning calorimetry (DSC), and low-angle x-ray diffraction techniques. The data suggest that chain folds play a prominent role in both the α and γ processes but that other factors such as polydispersity and/or branching are also important.

Morphological factors exerting an effect on thermomechanical analyses of crystalline polymers are discussed for three kinds of samples with quite different morphologies. (1) Bulk-crystallized linear polyethylene (PE) with spherulitic structure shows an a absorption, which was shown to be composed of two absorptions, α1 and α2. Based on the super-structural characterization and viscoelastic behavior of a single crystal mat of PE, the α1 absorption was assigned to the deformation associated with mosaic block boundaries and the α2 absorption to the uniform shear deformation of lamellar crystals. (2) Highly oriented and well crystallized poly-[p-(2-hydroxyethoxy)benzoic acid] shows the α → β crystal transformation caused by drawing stress. The role of tie links translating the stress along the fiber axis was proved by calculating the mechanical dispersion behavior of the dynamic modulus based on the super-structural parameters. (3) Oriented crystallites of PE prepared from dilute solution with a shis...

A renewed explanatory study is reported on the fold structure and branch location in single crystals of an ethylene–propylene copolymer by means of the ozone degradation method. By analogy with concurrent studies on linear polyethylenes a distribution of fold lengths is inferred, this distribution being broader, more uniform, and spreading deeper into the crystal interior in the case of the copolymer than for the linear polyethylene. Perhaps the most salient points of the work is that in contrast to nitric acid the oxidation by ozone does not obscure then characteristic CH3 infrared absorption band enabling the branch content to be followed during degradation. The single exploratory experiment of the present work reveals that while there is a certain amount of preference for the branches to accumulate near the fold surface, a substantial portion of them can still be located in the crystal interior. The potential of the present method for a more systematic study is indicated.

Crystalline polymers show a remarkable strain hardening in its plastic deformation compared with metals. In the case of metals, the power law holds between true stress and true strain, the power law index of which is lower than one (1). True stress tends to saturate with increasing true strain. Polymer chain shows very high modulus and high bonding energy along molecular axis, whereas intermolecular force is weak and the modulus perpendicular to the molecular axis is about one hundredth of that along molecular axis. With the progress of unfolding of molecular chains from folded structure in lamellar crystals, the deformation stress increases rapidly. To describe such a deformation process of crystalline polymers, it is especially necessary to employ true stress and true strain instead of nominal stress and nominal strain. In our previous paper (2), we have presented the equation to describe the true stress-strain relationship in a very simplified form, which was verified for linear polyethylene (HDPE) and nylon 6. In this paper, we have examined the applicability of our equation to isotactic polypropylene (PP), polyoxymethylene (POM) and polytetrafluoroethylene (PTFE).

Apparatus has been developed for studying the development of crystallinity and orientation during the melt spinning of synthetic fibers. Tension in the fiber and temperature, diameter, and x-ray diffraction patterns are measured as a function of distance from the spinneret for a running monofilament. Measurements are presented for linear polyethylene over a range of spinning variables together with other investigations carried out on the final as-spun fibers. These data indicate that the development of crystallinity in polyethylene is controlled by a balance between increased crystallization kinetics caused by the stress in the fiber and a tendency for increased supercooling with change in any spinning variable that increases cooling rates in the fiber. The type of crystalline orientation observed, its development during the spinning process, and the changes observed with changes in spinning conditions suggest a model for the as-spun fiber structure in which varying amounts of row nucleation and twisting of lamellar, folded-chain crystal overgrowths occur depending on the spinning conditions. As-spun fiber birefringence was shown to depend primarily on the crystalline orientation. Mechanical properties correlated well with c-axis crystalline orientation function and spinline stress.

Considerable confusion exists in the literature concerning the glass temperature, Tg, of many highly crystalline polymers, in particular, linear polyethylene (PE), poly(vinyl fluoride) (PVF), poly(vinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), poly(oxymethylene) (POM), and poly(ethylene oxide) (PEO). We attempt to resolve some of this confusion first, by defining the nature of the problem; second, by developing criteria for defining the locations along a relative temperature scale (T/Tg or T/TM) of the key relaxations and transitions, Tg, T < Tg, TM, and Tαc for C-C and CO backbone polymers free from long alkyl side groups; third, by developing a set of typical mechanical relaxation spectra for amorphous, semicrystalline, and single crystal materials of known Tg; fourth, by defining the concept of a double glass transition with values Tg(L) and Tg(U) and the optimum conditions for observing same. Finally, we apply these concepts and criteria to resolving the value of Tg for PVF and PVDF. Criteria employed include ratios of relaxation temperatures such as (T < Tg)/Tg, Tαc/TM, and Tg/TM, typical activation enthalpies for various relaxation processes, thermal expansion and heat capacity data. Two theoretical subjects are explored: the effect of crystallinity on increasing Tg and the effect of crystallinity on the relative strengths of the Tg and T < Tg processes. We also employ a “comparative anatomy” technique of comparing temperatures and related activation enthalpies of the several relaxations and transitions for a series of closely related polymers such as PE, PVF, PVDF, PTFE, Polytrifluorochloroethylene, and poly(vinyl chloride). We suggest that a new scientific discipline of interpreting the relaxation spectra of crystalline polymers may be emerging through integration of a large body of literature, the refinement of old criteria, and the development of new criteria. Even so, we are not yet able to offer a satisfactory interpretation of the relaxation spectra for POM and PEO.

10-fold hot stretched (80 °C) linear polyethylene (PE) was prepared for high precision AEG-Guinier-Jagodzinski camera by cutting into 0.1 mm thick slices. Now the line profiles of allhk0-reflections were clearly separated and analysed using the paracrystalline theory. The slices were first annealed at 120 °C and then irradiated under vacuum with 10, 100 and 300 Mrad ofCo 60. The lattice parameters increase remarkably in full agreement withKobayashi. The paracrystallineg-values increase mostly orthogonal to the (110) net planes and no microstrains are generated. The average size of the microparacrystallites increases at least until 100 Mrad. In connection with former experiments about the affine transformation of molten PE we conclude that the crosslinks are produced predominantly within the paracrystallites. A model is discussed.

Dependence of the glass-transition temperature, Tg, on polymer chain flexibility predicted by the Gibbs-DiMarzio theory was empirically tested by studying the relationship between Tg and the stiffness parameter for isolated chains, [sgrave]. It was found that [sgrave] is not a single variable controlling Tg for different polymer series which have different free volume fractions at Tg as a result of intrinsic differences in packing density in the crystalline state. The results obtained suggest that Tg of linear polyethylene lies near 160°K. A functional form of dependence of Tg on chain stiffness parameter and on local chain packing coefficient at Tg is proposed.

The glass transition of an irradiated, ultra-high molecular weight, linear polyethylene was investigated by means of the Perkin-Elmer DSC-2 differential scanning calorimeter. The experimental specific heat data were compared with those of the nonirradiated sample, obtained by DSC and adiabatic calorimetry.

An assessment is made of the information provided by n.m.r. second moment, fourth moment and T2 measurements on oriented samples of branched and linear polyethylene. Detailed theoretical comparisons are made with the previously reported experimental results of a number of workers in order to derive information about the molecular motions which underlie the α, β and γ relaxations in the two forms of the polymer. Plausible motional models are presented in each case. Particular attention has been given to the β relaxation which is explained in terms of lamellar fold motion. The relative sensitivity of the various n.m.r. measurements to molecular anisotropy and motion in the polymer is discussed.

It is shown with reference to linear polyethylene that the deformation of an oriented crystalline polymer takes place as a result of elongation of the coiled parts of the macromolecules in the amorphous zones owing to conversion of gauche into extended trans isomers. The decrease in coiled isomer content when the specimen is deformed by approximately 5% is accompanied by a small number of chemical bond breakages. Repeat deformation by the same amount does not result in any additional breakage of polymer chains.

A new preparative liquid-phase chromatograph, operating at a high temperature (160°C), allowed us to fractionate a linear polyethylene sample in narrow fractions (polydispersity about 1.1). These fractions, characterized by viscosity, light scattering, osmometry, and GPC measurements, can be used to calibrate any analytical GPC, i.e., to determine the variation of molecular weight and axial dispersion versus the elution volume.

Small-angle light scattering experiments were conducted on thin films of linear polyethylene fractions over a very wide range of molecular weights. Spherulitic structures were found in all samples with molecular weight 9 × 105 or less. A rodlike morphology predominates for molecular weights between 1 × 106 and 2 × 106. Still higher fractions yield a very disordered superstructure. These results can be correlated with previous studies of the overall crystallization rates and the resulting properties.

The transport equations for a power law fluid are used to solve the transient and non-isothermal problem of filling a disk-shaped cavity. Using the results obtained it is possible to predict gate pressures, fill times and short shots. Furthermore, the velocity and temperature fields can be obtained throughout the filling process. This information specifies the formation of a frozen surface layer during filling. Rigid PVC was primarily used in the simulations, but some results are also given for linear polyethylene, nylon 6–6, ABS and polystyrene.

An array or continuum of molecular weight distributions was set up, based upon the numerical solutions found for the theoretical log-normal (LN) and generalized exponential (Gex) distribution functions, for a range of Mw/Mn = H ratios. For the Gex distributions, m > 0 in the continuum, and the theoretical Schulz–Zimm and Tung–Weibull distributions, in which m ≥ 1 for H ≤ 31, are located within the continuum. The LN distribution is the broadest, and the Gex-related distributions become narrower as the numerical value of m increases. From literature data for polystyrene, poly(vinyl chloride), linear polyethylene, and polypropylene, one can assign to these polymers specific molecular weight distributions that fall within the continuum.

For linear polyethylene films elongated by 1500%, initial films and films annealed at a pressure of 7 t/cm2 at 250–270° initial m. p. (Tmelt) (eliminating effects of overheating and recrystallization) and dimensions of crystallites were determined in the direction of the L002 chain. A linear relation was derived between Tmelt and L002 according to the Thomson equation. The equilibrium value of Tmelt = 143·6° and free surface energy of the end surface of crystallites σe = 104 erg/cm2 was determined.

The application of an oligomer as an internal standard in gel permeation chromatography was studied on narrow low molecular weight fractions of linear polyethylene using n-decane as the standard. A Waters gel permeation chromatograph was run continuously at 130°C with 0-dichlorobenzene as solvent. It has been found that the values of the elution volume of given samples vary with time and that a simple correction using n-decane as an internal standard reduces the inaccuracy from the original 6% to less than 1%. The corrected elution volumes remain reproducible over a period of several months so that frequent calibration is eliminated. The use of the oligomer chemically similar to the polymer samples gives a much better result than the use of low molecular weight impurity as the standard.

Electron microscope studies are reported for crystals of linear polyethylene formed in dilute solution from very sharp low molecular weight fractions. Emphasis is placed on molecular weights in the range of 1.1 × 103 to 15.1 × 103. The dependence of the crystal habit on the crystallization temperature is very similar to that which has been found for the higher molecular weight species. However, the demarcation temperature for the crystallization of the different morphological forms is very molecular weight-dependent. The conditions under which interfacial dislocation networks form can be clearly defined. The molecular weight must be less than 3000, so that these structures are restricted to very small chain lengths. However, not all crystallization conditions within this allowable molecular weight range yield such dislocations. The formation of interfacial dislocation networks are shown to occur only under very special circumstances. Their occurrence clearly cannot be offered as evidence, as has been done in the past, for a regular, chain-folded interfacial structure.

A systematic investigation of the effect of molecular weight and molecular weight distribution on the cold drawing behaviour of linear polyethylene has been undertaken. In the molecular weight range studied, the natural draw ratio was very sensitive to the morphology of the initial material; spectacular effects on the natural draw ratio were observed provided that an optimum initial morphology was achieved. These effects can be related to both molecular weight and molecular weight distribution. The extensional modulus and melting behaviour of the drawn material was also examined. To a first approximation the extensional modulus related to the natural draw ratio, and at very high draw ratios (∼30) extremely high extensional moduli (∼700kbar) were obtained. The structure and properties of the drawn material did, however, also depend on the molecular weight and molecular weight distribution. In particular, when certain molecular weight requirements were satisfied, the oriented samples showed the presence of extended chain material. It does, however, appear that although differences in molecular weight and molecular weight distribution give rise to differences in extensional moduli, the presence of extended chain crystallization per se is not a necessary requirement for the production of high modulus material.

The structure of real fibres is examined in relation to the crystallinity of some idealized models of substances and the distortions which they may undergo. Sections of the treatment deal in order with fundamental theory, distortions of the first kind and degree of crystallinity, the concept of a paracrystal and distortions of the second kind, paracrystalline macrolattices, paracrystals in atomic dimensions, the amorphous lattice, and the structure of linear polyethylene including results of some recent work in the laboratory.

Fibrillar crystals of polyethylene are prepared by stirring solutions of the polymer in xylene at elevated temperatures. Extraction of these crystals with xylene at controlled temperatures is a convenient method of preparing narrow fractions of linear polyethylene of molecular weights below 105. Higher molecular weight fractions were readily obtained by column fractionation but not by the extraction of fibrillar crystals.

The solubility constants for thirteen permanent gases were measured within the temperature range 5–55°C. in a linear and a branched polyethylene, hydrogenated polybutadiene, and natural rubber. Equilibrium and time lag solubility determinations were made, the latter being indirectly obtained as the ratio of the permeability to the diffusion constants. Within experimental precision, equilibrium and time lag measurements were in agreement. The solubility of each gas in polyethylene was found to be proportional to the volume fraction of amorphous material when the polymer was treated as a simple, two-phase mixture of crystalline and amorphous polymer, each with a characteristic specific volume. Even the small helium molecule exhibited no detectible solubility in the crystallites according to this model. Therefore, a solubility constant in completely amorphous polyethylene could be determined for each gas which, with the density of an arbitrary sample, would enable calculation of the solubility of each gas in that particular sample. A correlation of the solubility constants in completely amorphous polyethylene was obtained from a thermodynamic model of the disolution process. Comparison of this correlation with a similar one for normal hydrocarbon liquids emphasized the analogy between the amorphous phase in polyethylene and these low molecular weight substances. The solubility constants in natural rubber, a completely amorphous polymer under the experimental conditions, were approximately 50% higher than those in amorphous polyethylene. Higher intermolecular forces due to the unsaturation in natural rubber may account for this result. The apparent heats of solution of all gases in branched polyethylene were approximately 1.0 kcal./g. mole more positive than those in linear polyethylene. This behavior was shown quantitatively, by comparison with dilatometric data, to be simply the result of crystalline melt-out in branched polyethylene. In linear polyethylene the experimental solubility data yielded essentially true heats of solution, since negligible crystalline melt-out occurred between 5 and 55°C. These were correlated quite satisfactorily by further application of the thermodynamic model for the dissolution process. Available evidence, therefore, indicates that the crystallites in polyethylene are impenetrable, and are randomly distributed on a macroscopic scale with respect to the diffusion and dissolution processes. The amorphous phase behaves as a homogeneous liquid whose thermodynamic properties are independent of the mode of polymer preparation, thermal history of the sample, and level of crystallinity.

Solubilities and diffusivities of N2, O2, CO2, and He in a variety of polyethylenes were measured in the temperature range 0–50°C. Polyethylene films studied covered a range of crystallinities (43–82%) and branching indices, and were prepared under a variety of known thermal histories. Diffusivities were determined by the time-lag method; solubilities, by time-lag, and also by a newly developed and more accurate static method. Solubilities were found to obey Henry's Law; the solubility constants determined by both methods were found to agree within the limits of accuracy, confirming the applicability of the unsteady-state diffusion equation to essentially isotropic crystalline polymers. For a given gas at constant temperature, the solubility constant is directly proportional to the volume fraction of amorphous material in a polyethylene sample (as determined by density), irrespective of its origin or thermal history; the concept of the crystallites as an impermeable, dispersed phase thus appears justified. Diffusivities were found to vary widely (nearly fivefold) depending on polymer crystallinity and thermal history and were as much as tenfold lower than the values estimated for completely amorphous polyethylene. Application of principles of flow through porous media to this system leads to a conclusion that abnormally low diffusivities arise predominantly from the impedance to gas flow offered by the dispersed crystalline phase. Variations in diffusivity with branching index and thermal history correlate qualitatively with expected corresponding variations in crystallite growth kinetics and shape; the existence of highly anisometric, laminar crystallites in annealed linear polyethylene is indicated from these studies. The combined influence of crystallinity on solubility and diffusivity permits as much as a tenfold variation in gas permeability of polyethylene depending on polymerization method or fabrication process.

Linear polyethylene crystallized from the melt or heat-treated at temperature above 110°C. shows in the DTA thermogram an additional endothermal maximum Tm1 at a temperature lower by 10 to 20°C. compared with the normal maximum Tm0. The appearanee of Tm1 depends on the crystallization temperature, time, and temperature of heat-treatment. For a constant crystallization time, the difference between Tm0 and Tm1 decreases with increasing of the crystallization temperature; at a constant crystallization temperature it increases with the crystallization time. By treating those specimen with two endothermal maxima at a temperature near that of Tm1, Tm1 splits into two peaks. This effect is interpreted by the assumption, that those crystalline regions which first correspond to the Tm1 maximum, partly form more stable crystals of greater thickness and higher melting point, and partly melt with subsequent formation of little crystallites of lower melting point during cooling. Under suitable conditions, the three endothermic peaks also can be observed with branched polyethylene. Bei Temperaturen oberhalb 110°C isotherm aus der Schmelze kristallisiertes oder getempertes lineares Polyathylen zeigt im DTA-Thermogramm ein zusatzliches, endothermes Maximum Tm1 bei einer um etwa 10 bis 20°C gegenuber dem normalerweise gefundenen Maximum Tm0 niedrigeren Temperatur. Das Auftreten von Tm1 hangt von Kristallisationstemperatur, Zeit und Tempertemperatur ab. Die Temperaturdifferenz zwischen Tm0 und Tm1 wird, bei gleicher Kristallisationszeit, mit steigender Kristallisationstemperatur geringer und wachst, bei konstanter Kristallisationstemperatur, mit der Kristallisationszeit an. Wenn man eine Probe, die zwei Maxima zeigt, auf eine Temperatur nahe der von Tm1 erwarmt, so spaltet Tm1 selbst wieder in zwei Maxima auf. Diese Tatsache wird durch die Annahme erklart, das in dem kristallinen Gefuge gewisse Teile der kristallinen Bereiche, die ursprunglihch Tm1 zuzuordnen waren, durch Dickenwachstum der Lamellen stabilere Kristalle bilden, deren Schmelzmaximum bei hoherer Temperatur liegt, wahrend andere Anteile aufschmelzen und beim Abschrecken rekristallisieren. Das Auftreten dieser Maxima kann unter geeigneten Bedingungen auch bei verzweigtem Polyathylen beobachtet werden

With the aid of a modified Sofica light-scattering apparatus an investigation was carried out of the crystallization of polyolefines from dilute solutions in several solvents. The intensity of the light scattered at various angles was determined as a function of time in the initial period of crystallization. Both linear polyethylene and polypropylene in p-xylene and in 1-chloronaphthalene showed the formation of disk-shaped crystals, which, after their formation, rapidly grew.

The equilibrium amount and the rate of adsorption of a dispersed dye, Whitex were measured at 80°C for linear polyethylene(PE) films to discuss the correlation between the sorption properties and the molecular orientation in the amorphous regions.The PE specimens which were drawn at 60°C in various draw ratios ranging from 1.0 to 10.0 were prepared for the subsequent dyeing.In the comparatively earlier stage of the sorption, the rate of adsorption of Whitex obeyed Fick's law to result in the diffusion constant D. The diffusion constant D dropped remarkably with draw ratios, whereas the amount of equilibrium sorption Q∞increased monotonically.These results were explained in terms of the following two points of view: 1 the increase in the energy of amorphous regions with molecular orientation and 2 the decrease in the free volume and the increase in voids with drawing.

The deformation of polyethylene films with spherulites was investigated by electron and polarising microscope. A linear polyethylene, Hizex 5000 was disolved in xylene at above 120°C and films were prepared on a piece of hot glass at 110°C and then cooled slowly to room temperature. (for 2-3 hours). The sperulitic films were drawn with various ratio at 20°C and 60°C. The deformation behaviour of the films at room temperature depends on the crystallization condition.The results obtained are as follows., 1) No deformation of spherulites was observed by polarising microscope in the range within the elastic limits at 20°C and 60°C.2) In the range where the strain is proportional to stress, the deformation of spherulites starts from the center at both temperature.3) In the high stretching the extinction ring was observed in the necking part. This indicates that the crystal lamellae remains without unfolding.4) When cross nicol is set in the direction of 45° to the drawing direction, the angle between the cross extinction lines observed in necking part becomes smaller than 90°.5) In lower stretching the extension of spherulite is of affine deformation.

The P–V–T relations are measured for linear polyethylene over the temperature range from 20 to 230°C and for eicosane from −30 to 120°C under hydrostatic pressures up to 800 kg/cm2, using a pressure apparatus which is equipped with pyrex glass windows and a dilatometer. From the results the thermal expansion coefficient, α, compressibility, β, and internal pressure, Pi are obtained and their temperature dependences of polyethylene and eicosane are compared with each other. These quantities show Mype changes in the melting region which are broad for polyethylene and narrow for eicosane. α is more sensitive than β to the premelting, and as a result Pi begins to increase at a temperature as low as 50°C for polyethylene.Pi of eicosane in the solid state is smaller than that of polyethylene. Pi of each sample in the liquid state is not proportional to V−2 but to V−6 for polyethylene and to V−2.45 for eicosane.

Molecular motion has been studied in a highly branched polyethylene, DYNK, and in a linear polyethylene, Marlex 50. The studies centered around the use of nuclear magnetic resonance spectroscopy, with additional information from measurements of x-ray diffraction, dielectric relaxation, and the diffusion of small molecules into the polymers. The nuclear resonance studies extended over a temperature range of 80 to 410°K., and studies by the other techniques included some measurements at low and high temperatures. It is shown that crystallinity in the linear polyethylene persists to within only a few degrees of the “melting point” of the gross polymer, and that chain rotation within the crystallites is comparatively restricted until shortly below the temperature of fusion. On the other hand, chain rotation within the crystallites of the branched polyethylene is much freer, presumably due to the presence of lattice defects, such as might be caused by the incorporation of branch points into the crystallites. Crystallinity in the branched polyethylene disappears at much lower temperatures than in the linear polymer. There is considerable motion of chain segments within the amorphous regions of both kinds of polyethylene, although at a given temperature the linear polymer exhibits more constraint than does the branched polymer. It is evident that the amorphous portions of both polymers possess the attributes of a viscous liquid, even at temperatures well below the melting point of the gross material. Activation energies and frequency factors for the motions of chain segments in the amorphous portions have been computed and are compared with the data from earlier measurements of dielectric and mechanical relaxation.

Samples of commercial plastics have been bombarded by short pulses of nonpenetrating electrons. Observations of charge transients representing the long‐lived component of the induced current lead to the following conclusions: (i) One carrier species is rapidly and strongly localized; (ii) the mobile excess carriers decay by bimolecular recombination; (iii) although such carriers cannot in practice complete transits through the thickness of the samples, they can be swept out of the excited layer into the bombarded electrode. This paper fully explains how the sweep‐out time, and from it the effective carrier mobility and generation efficiency, are deduced. The mobilities, with the sign of the mobile carrier, are polystyrene (20°C), μ+=1.0×10−6 cm2/V sec; polyethylene terephthalate (20°C), μ−=1.5×10−6 cm2/V sec; linear polyethylene (80°C), μ+=4.5×10−10 cm2/V sec. The temperature dependence of mobility is studied in the first two materials.

An additional crystalline phase has been found to form in linear polyethylene-dotriacontane blends, based on differential thermal analysis (DTA) data. The new phase is formed when blends containing linear polyethylene, at concentrations less than 34 per cent, are solidified from the melt under carefully controlled crystallization conditions. The endotherm of the new phase, as measured by the DTA, occurs at 2–5° lower than that of polyethylene. The quantity of the new crystalline phase has been found to be dependent upon polymer molecular weight, blend concentration, solidification rate and heat treatment. Blends having lower molecular weight fractions enhance the formation of the new phase. The relative amounts of the new crystalline phase and the polyethylene crystalline phase vary with the cooling rate of the blend during solidification, with the new crystalline phase predominating at slower cooling rates. Heat treatment of the solidified blend results in the merging of the polyethylene and the new crystalline phase endotherms.

Improved methods for measuring weight- and number-average molecular weight of polymers soluble only at elevated temperatures are applied to selcted samples of polyethylene. For two samples of essentially linear polyethylene, number-average molecular weights by cryoscopy are 11,500 and 13,000, and weight-average molecular weights by light scattering are 144,000 and 175,000. For samples of branched Fawcett-type polyethylene, number-average molecular weights are in the range 10,000–19,000 and weight-average molecular weights are between 300,000 and 700,000. For one sample each of branched and essentially linear polyethylene it is demonstrated that light scattering measurement in three solvents gives the same molecular weight: no evidence is found for the “association” of these samples of polyethylene in thermodynamically poor solvents. It is thus demonstrated that association is not observed for all samples of polyethylene in dilute solution in α-chloronaphthalene.