Showing papers in "Journal of Macromolecular Science, Part B in 1970"
TL;DR: In this paper, X-ray diffraction has been used to determine the crystal structure of poly(vinylidene fluoride) phase II, and three principal chain conformations were considered, which included two 21 helical forms [degenerate (planar) and nondegenerate] and the trans-gauche-trans-gaueche' form.
Abstract: In this study, X-ray diffraction has been used to determine the crystal structure of poly(vinylidene fluoride) phase II. Three principal chain conformations were considered, which included two 21 helical forms [degenerate (planar) and nondegenerate] and the trans-gauche-trans-gauche' form. An X-ray crystal structure determination has shown that the trans-gauche-trans-gauche' (TGTG′) conformation is the correct one for phase II. Experimental X-ray intensity data were taken at both −145° and 20° C in order to study the effect of temperature on the resulting structure. From the comparison between observed and calculated intensities, there are two possible crystal symmetries, P21 and P1, depending upon whether the two chains are taken to be antiparallel or parallel to one another. For both cases, the reliability indices for the chosen structure are almost identical. For either symmetry the unit cell is metrically orthorhombic (all angles equal to 90° within experimental error) with the following latt...
115 citations
TL;DR: In this paper, the authors investigated the Crystallization kinetics of molten polyethylene subjected to a constant shear stress and showed that the rate of crystallization depends on the difference of entropy (Δs) between the crystalline and molten states.
Abstract: The Crystallization kinetics of molten polyethylene subjected to a constant shear stress were investigated theoretically and experimentally. The rate of crystallization depends on the difference of entropy (Δs) between the crystalline and molten state. The constant shear stress in the melt decreases Δs causing an abrupt increase in the rate of crystallization and a decrease of the thickness of the folded-chain lamellar crystals.
107 citations
TL;DR: In this article, the authors applied infrared spectroscopy to discuss the orientation, the crystallinity, and the conformation of chain segments in the amorphous regions in drawn high-density polyethylene.
Abstract: Infrared spectroscopy is applied to discuss the orientation, the crystallinity, and the conformation of chain segments in the amorphous regions in drawn high-density polyethylene. The orientation of the crystals as well as the crystallinity are derived from the dichroism and the absorbance, respectively, of the band at 1894 cm-1. The orientation and some aspects about the conformation of the chain segments in the amorphous regions can be obtained from the bands in the 1400-1300 cm-1 region (gauche) and at 1078 cm-1 (gauche and trans). The dichroic studies show a high degree of orientation increasing with draw ratio λ for the chain segments in the crystals, but a low orientation reaching saturation at λ between 5 and 10 for those in the amorphous regions. The experiments indicate a change in crystallinity during the drawing process which depends on the thermal treatment of the undrawn sample. In the amorphous regions the number of CH2 groups in gauche conformations decreases up to λ between 10 and...
75 citations
TL;DR: In this article, a series of polyamides as crystallized from solution is studied and it is shown that the fold length is determined by the number of hydrogen bonds between the stems.
Abstract: The present paper, dealing with nylons 66, 610, and 612, is part of a study on a series of polyamides as crystallized from solution. The lath-shaped crystallization products, aggregated in the form of sheaves, possess the characteristics of chain-folded single crystals. In particular, they can be collected in the form of oriented mats which display arced X-ray reflections both in the wide- and low-angle regions. This enables the fold surfaces to be indexed as 00l. In a given polymer the long spacing has a characteristic value and for different polymers it varies in the ratio of the monomer lengths. The measured layer thickness corresponds closely to four-unit cell lengths. The fact that this holds for all three polymers implies that the fold length is determined by the number of hydrogen bonds between the stems. In view of the small value of this figure (due to the large identity period) the long period can only be apportioned between straight stems and folds in a limited number of ways which ena...
74 citations
TL;DR: The morphology of glassy amorphous thin polycarbonate film cast from solution is affected by thermal treatments as mentioned in this paper, which results in an increase in the size of the ordered regions, nodules, up to several hundred Angstroms.
Abstract: The morphology of glassy amorphous thin polycarbonate film cast from solution is affected by thermal treatments. Annealing above 80° C and below Tg results in an increase in the size of the ordered regions, nodules, up to several hundred Angstroms. The crystallization process from the glass, taking place at 145° C, is divided into three major steps. At first the nodules merge into patches which aggregate to form lamellar planar structures. In some cases the planar structures are well-formed single crystals. Following this, spherulitic arms develop from the planar structures as centers. These arms at first consist of aggregates of large nodules which recrystallize to form lamellae; the final morphology is spherulitic in nature. The effect of film thickness and of several substrates on the morphology has been observed. Applying stress at room temperature to the crystalline film results in a breaking up of the lamellae into small blocks.
73 citations
TL;DR: In this article, high-density commercial polyethylenes have been crystallized under the combined orientation and pressure effects available in the Instron capillary rheometer, and the samples so formed were found to ha...
Abstract: High-density commercial polyethylenes have been crystallized under the combined orientation and pressure effects available in the Instron capillary rheometer. The samples so formed were found to ha...
72 citations
TL;DR: In this article, a small-and wide-angle X-ray investigation of drawing and annealing of polypropylene quenched films in wide ranges of draw ratio (λ = 1-20) and of temperature (20°-150°C) shows the discontinuity of the elementary act of transformation in the microneck of the original lamella.
Abstract: Small- and wide-angle X-ray investigation of drawing and annealing of polypropylene quenched films in wide ranges of draw ratio (λ = 1-20) and of temperature (20°-150°C) shows the discontinuity of the elementary act of transformation in the microneck of the original lamella of the microspherulitic into the microfibrils of the final fiber structure. The long period, the orientation, and the crystalline disorder change abruptly. The continuity of macroscopical deformation in the neck is a consequence of superposition of the effects of a great many microneck zones which are more or less randomly scattered over the whole neck area. In the first stages of plastic deformation before the appearance of micronecks the lamellae parallel to the draw direction are compressed and those perpendicular to the draw direction become physically separated. This was checked by noting the drastic reduction of scattering after the introduction of dodecane which fills the holes between lamellae created in the initial st...
70 citations
TL;DR: In this paper, it was shown that the row nuclei are fibers, only about 200 to 300 A in diameter, extending for distances up to 10 mU, and their presence determines whether the sample will crystallize spherulitically or into a row-nucleated morphology.
Abstract: Crystallization from a stressed polymer melt produces not the familiar randomly nucleated spherulitic structures, but instead a highly oriented “row-nucleated” morphology. We have crystallized films of polyoxymethylene from stressed melts; just as polyethylene, the surfaces are covered with protruding lamellar edges highly oriented in the extrusion direction. There is no evidence for the more familiar spherulitic morphology. Electron microscopy directly revealed for the first time that the row nuclei are fibers, only about 200 to 300 A in diameter, extending for distances up to 10 mU. Although comprising a negligibly small amount of total sample volume, they are of prime importance in influencing how the sample will crystallize. Their presence determines, more than any other single factor, whether the sample will crystallize spherulitically or into a row-nucleated morphology. When deformed in the extrusion direction, the twisted lamellar bundles open up to form a fishnetlike structure. Simultaneo...
62 citations
TL;DR: A detailed study of high pressure-crystallized poly(vinylidene fluoride) has indicated that a mixture of low-melting phase II and high-melts phase I is present, rather than a new crystalline phase (phase III) as originally suggested.
Abstract: A detailed study of high-pressure-crystallized poly(vinylidene fluoride) has indicated that a mixture of low-melting phase II and high-melting phase I is present, rather than a new crystalline phase (phase III) as originally suggested. The relative amounts of phase I and phase II resulting from crystallization under pressure are a function of pressure and the degree of supercooling. Pressure crystallization at 285°C and 5500 atm results in samples which were pure phase I with an increased melting point of 187°C.
61 citations
TL;DR: In this article, the rotational motion of the chain segments around the molecular axes is considered to explain the X-ray diffraction pattern of the high-temperature form of trans-1,4-polybutadiene.
Abstract: It is known that trans-1,4-polybutadiene shows a crystal transformation at about 76°C. The crystal structure of the high-temperature form of trans-1,4-polybutadiene has been studied by X-ray diffraction. The chain conformation of the high-temperature form is similar to that of the low-temperature form. Above the crystal transformation temperature, the CH2─CH2 bond remains trans, but the internal rotation angles around two CH2─CH bonds are decreased to 80° and −80° from 109° and −109°, respectively. The molecular chains, however, are considered to be in a considerably distorted state due to torsional oscillation about the C─C bonds. It is shown that the X-ray diffraction pattern of the high-temperature form can be explained by taking into account the rotational motion of the chain segments around the molecular axes.
53 citations
TL;DR: The infrared spectrum of a solvent-cast film of commercial polyvinyl chloride (PVC) can be very sensitively compared to a rapidly quenched film of the same material by using a compensation technique as discussed by the authors.
Abstract: The infrared spectrum of a solvent-cast film of commercial poly(vinyl chloride) (PVC) can be very sensitively compared to a rapidly quenched film of the same material by using a compensation technique. When this is done, crystalline bands, as seen in urea canal complex PVC, can be detected and measured in the solvent-cast film. The melting and recrystallization behavior as well as the broad melting range from 120° to 210°C indicate the presence of crystallites of widely different degrees of perfection. Crystallization kinetics from the quenched glassy state indicate that time-temperature superposition applies with an activation energy of 90 kcal/mole. Molecular mobility is indicated as the rate-controlling mechanism.
TL;DR: In this article, a general structural state deformation model was developed for characterizing mechanical behavior of polypropylene fibers and uniaxially drawn isotactic polyethylene films.
Abstract: This investigation introduces quantitative morphological criteria for defining the structural state of a polymer sample and develops a general structural state deformation model for characterizing mechanical behavior. This general model discards the present fragmented view of the autonomy of observed mechanical processes (yielding, fracture, recovery, etc.) and brings the fabrication process, the mechanical tests, and even the construction of the sample (fiber or film) into focus as simply different aspects of a single process of deformation. The fabrication, fracture, yielding, and recovery behavior of two series of uniaxially drawn isotactic polypropylene films and two series of drawn isotactic polypropylene fibers, totaling thirty different structural states, have been deter-mined. The structural state of each of these samples is known quantitatively. The measurements were made over a range of strain rates from 1 to 1,000,000%/min and temperatures from 23° to -196°C. This study has resulted in...
TL;DR: In this article, the fusion behavior of lightly cross-linked polyethylene films isothermally crystallized at various temperatures and extensions has been examined on a differential scanning calorimeter (DSC).
Abstract: The fusion behavior of lightly cross-linked polyethylene films isothermally crystallized at various temperatures and extensions has been examinedonadifferential scanning calorimeter (DSC). Ameans to hold the specimen at fixed elongation during the melting was devised. At large extensions, a separate higher-temperature endotherm was observed in addition to the major peak, indicating a two-phase nature of the crystal morphology. In addition, crystallization experiments performed on the DSC show the crystallization process to consist of two stages. In contrast to reported results for natural rubber and polychloroprene, the melting temperature for polyethylene was not found to be strongly dependent on crystallization temperature or extension. The reason for the differences between polymers is not presently understood, but they may reflect variations in morphological details.
TL;DR: In this article, the free volume quantities proposed earlier by Boyer and Simha in connection with the glass transition are reformulated by taking into account the temperature dependence of the thermal expansivities α l and α g for the liquid and the glass, respectively.
Abstract: Free volume quantities proposed earlier by Boyer and Simha in connection with the glass transition are reformulated by taking into account the temperature dependence of the thermal expansivities α l and αg for the liquid and the glass, respectively. This necessitates an extrapolation of the liquid to temperatures below Tg which is performed by means of the reduced volume-temperature function established and given a theoretical foundation previously. For the glass, low temperature experimental data, encompassing all relaxations occuring below Tg, are required. Two polymer series are examined in detail, namely, poly(methacrylates) and poly(vinyl) alkyl ethers, where αg has been measured between at least 30°K and Tg. Results for poly(methylacrylate) and poly(styrene) are also given. The systematic decrease in the product (αl - αg) · T|T=Tg with increasing length of the side chain noted previously is considerably reduced but not eliminated when the appropriately corrected expression is substituted in...
TL;DR: There have been several previous studies of the dc conductivity of poly(ethylene terephthalate) as mentioned in this paper, and the results indicate the difficulties inherent in this measurement: several authors [1,2] found evidence for ionic conduction through a hopping process; others [3,4] proposed conduction by electrons injected through a barrier.
Abstract: There have been several previous studies of the dc conductivity of poly(ethylene terephthalate). Disagreement among the various authors indicates the difficulties inherent in this measurement: several authors [1,2] found evidence for ionic conduction through a hopping process; others [3,4] proposed conduction by electrons injected through a barrier.
TL;DR: The high-pressure melting behavior of samples of vinylidene fluoride copolymerized with vinyl fluoride, trifluoroethylene, or tetrafluorethylene indicate that the copolymers have a lower entropy of melting than the poly(vinylide fluoride) homopolymers in the same phase.
Abstract: The high-pressure melting behavior of samples of vinylidene fluoride copolymerized with vinyl fluoride, trifluoroethylene, or tetrafluoroethylene indicate that the copolymers have a lower entropy of melting than the poly(vinylidene fluoride) homopolymers in the same phase. As the comonomer size increases, the entropy of melting decreases. High-pressure crystallization of copolymers of 91-9 mole% vinylidene fluoride-trifluoroethylene and 93-7 mole% vinylidene fluoride-tetrafluoroethylene results in a high-melting form of phase I (planar zig-zag).
TL;DR: In this article, the crystallization of glassy amorphous thin polycarbonate films quenched from the melt has been followed by the formation of structures similar to those observed during the crystallisation of films containing small amount of adsorbed solvent.
Abstract: The crystallization of glassy amorphous thin polycarbonate films quenched from the melt has been followed. Structures similar to those observed during the crystallization of films containing small amount of adsorbed solvent are formed. However, crystallization, at the same temperatures, is much slower and more irregular. Preannealing of the samples below Tg affects the crystallization process, increasing the nucleation rate. Annealing above Tg does not destroy all order gained by annealing below Tg.
TL;DR: In this paper, the transformation from the orthorhombic to the monoclinic structure has been observed by means of infrared spectroscopy in shaken preparations of single crystals of polyethylene, mixed polyethylenes and perdeuteropolyethylene.
Abstract: The transformation from the orthorhombic to the monoclinic structure has been observed by means of infrared spectroscopy in shaken preparations of single crystals of polyethylene, mixed crystals of polyethylene and perdeuteropolyethylene, and physical mixtures of single crystals of these two polymers. Annealing of such shaken samples results in the conversion of the monoclinic back to the orthorhombic structure, but with an accompanying change from the (110) folding characteristic of single crystals to (200) folding. The monoclinic structure thus appears to be an intermediate state in the fold-plane transformation which can occur upon deformation. Both unannealed and annealed physical mixtures give evidence of ciliary penetration.
TL;DR: In this article, a relation between the depolarization and the volume fraction crystallized has been derived taking into account the polycrystalline nature of the specimen and assuming uniaxially birefringent crystallites.
Abstract: One of the methods in use for measuring the kinetics of isothermal crystallization of polymers is the recording of the depolarization of plane-polarized light by a microscope specimen. A relation between this depolarization and the volume fraction crystallized has been derived taking into account the polycrystalline nature of the specimen and assuming uniaxially birefringent crystallites. Uniform, all-directional increase in size of the crystallites would cause the depolarization to follow an Avrami-type equation with the Avrami exponent one unit “too high.” For spherulitic growth the correct Avrami exponent is found on the assumption that the birefringent entities in the spherulites do not increase in size but only in number. The depolarization by a polycrystalline specimen of uniform particle size is proportional to both specimen thickness and particle size. The derived relations are tested by random number calculation and their limits of reliability are indicated accordingly.
TL;DR: The electron spin resonance (ESR) studies of mechanical degradation of crystalline polymer solids initiated by grinding [1,2], fracture, and mechanical stresses [3-7] have appeared as mentioned in this paper.
Abstract: In recent years, several electron spin resonance (ESR) studies of mechanical degradation of crystalline polymer solids initiated by grinding [1,2], fracture, and mechanical stresses [3-7] have appeared. Highly oriented fibers or films were used in the mechanical loading experiments. The general consensus is that under high stress the most strained chemical bonds in polymer chains are cleaved and macroradicals are formed. Each chain rupture produces two radicals which under favorable conditions may be observed by ESR. The presence of air (oxygen) or high chain mobility enhanced by high temperature and swelling agents can so efficiently destroy the radicals that the radical population never reaches the sensitivity limit of the ESR spectrometer. In the absence of such scaveging processes the primary radicals produced by chain reupture may still be rather unstable and tend to transfer their energy to other close-by groups. By such transfer, eventually very stable secondary radicals are formed which a...
TL;DR: In this article, the tensile creep behavior of amorphous, glassy polycarbonate based on bisphenol A was studied and the transition from linear to nonlinear behavior was characterized.
Abstract: The validity of the theory of linear viscoelasticity over the temperature range 20°-13°C has been tested by studying the tensile creep behavior of the amorphous, glassy polycarbonate based on bisphenol A. The stress threshold, beyond which the mechanical properties deviate from the predictions of linear theory by more than 3%, is found to decrease as the temperature approaches the vicinity of the glass transition temperature (149°C). Extension of the experimental time scale from 10 to 1000 sec likewise diminishes the stress level below which the linear theory is applicable. The onset of nonlinear behavior is marked by a clear increase in the isothermal, isochronous compliance with increasing stress. Such an increase in compliance with stress becomes gradually sharper at increasing stress levels until necking or failure of the specimen occurs. The analytical characterization of the transition from linear to nonlinear behavior, as well as certain molecular implications of such a transition, are dis...
TL;DR: In this paper, the physical structure of elastic "hard" fibers has been investigated in terms of the number of fibers and the properties of the fibers' elasticity and their properties.
Abstract: (1970). Physical structure of elastic “hard” fibers. Journal of Macromolecular Science, Part B: Vol. 4, No. 4, pp. 953-955.
TL;DR: In this article, the shrinkage of drawn bulk polyoxymethylene was studied by wide-angle and small-angle X-ray diffraction and electron microscopy as a function of the amount of draw.
Abstract: The shrinkage of drawn bulk polyoxymethylene was studied by wide-angle and small-angle X-ray diffraction and electron microscopy as a function of the amount of draw. Upon heating, the drawn material shrinks nearly instantaneously; the rtained strain increases with draw ratio. Small-angle patterns, including circuler, ellipsoidal, four-, six-, and two-point patterns, show various degrees of reversibility which decrease with increasing elongation especially above 100% draw. Wide-angle pole figures indicate changes in chain orientation distribution for samples drawn between 10 and 200% (the maximum examined). Deformation occurs primarily by several micronecking processes as well as lamellar and molecular slip. Morphological changes during shrinkage take place in all of the structural units formed by drawing. In addition to changes in spherulite dimensions, lamellar slip occurs, short fibrils disappear, and large diameter fibrils as well as lamellae normal to the draw direction form.
TL;DR: In this article, the authors showed that the acceleration of the strain rate with increasing strain (strain-softening) observed in yielding under a constant load is attributable to the perturbation of the annealed glass by strain.
Abstract: The strain rate of polymethyl methacrylate (PMMA) in yielding under a constant load varies by a factor of approximately 50 with the thermal history. PMMA cooled rapidly from above to below the glass transition temperature yields at a high rate; isothermal innealing of the quenched PMMA below Tg reduces the yield rate. The rate of gain of flow resistance is maximal near 95°C annealing temperature (Tg = 110° C). We expect straining, like quenching, to perturb the glass structure. Accordingly the acceleration of the strain rate with increasing strain (strain-softening) observed in yielding under a constant load is attributable to the perturbation of the annealed glass by strain. Quenching and small plastic strains as well reduce the density of PMMA by 10−4 to 10−3 g/cm3.
TL;DR: In this article, the frequency dispersion in the complex dynamic modulus functions of polyethylene terephthalate and related polymers over a frequency range from 0.05 to 50 cps was measured at various temperatures from −170° to 200°C covering the secondary glass transition, primary glass transition and crystal disordering temperatures of these polymers.
Abstract: The frequency dispersion in the complex dynamic modulus functions of polyethylene terephthalate and its related polymers over a frequency range from 0.05 to 50 cps was measured at various temperatures from −170° to 200°C covering the secondary glass transition, primary glass transition, and crystal disordering temperatures of these polymers. The results obtained were analyzed from the phenomenological view point of linear viscoelasticity on the basis of the following three assumptions: (1) additivity for assessing the contribution of each relaxation mechanism to the viscoelastic functions, (2) validity of the time-temperature superposition hypothesis within each relaxation mechanism independently of other relaxation mechanisms, (3) symmetrical loss modulus function of each relaxation mechanism with respect to logarithmic frequency. At least three distinctive mechanical dispersions associated with the secondary and primary glass transitions and the crystal grain boundary phenomena or crystal disor...
TL;DR: In this article, the Ziegler-Natta microfibrils were obtained by the crystallization of isotactic polystyrene from stirred solutions in 1,3,5-trimethylben-zene and cyclohexanol and were characterized by periodic lamellar overgrowths which gave rise to a discrete X-ray reflection having a d-spacing of 90 A.
Abstract: Fibrillar crystals have been prepared by the crystallization of isotactic polystyrene from stirred solutions in 1,3,5-trimethylben-zene and cyclohexanol. Similar microfibrils have been prepared in the nascent state by the polymerization of styrene in 1,3,5-trimethyl-benzene with a heterogeneous Ziegler-Natta catalyst. The microfibrils varied in width between 140 and 250 A and were characterized by periodic lamellar overgrowths which were believed to give rise to a discrete X-ray reflection having a d-spacing of 90 A. Thermal analysis suggested that high growth temperatures favored greater crystal perfection. During crystallization from stirred cyclohexanol solutions, a fractionation of high molecular weight chains occurred which was more efficient at higher crystallization temperatures. In comparison to crystallizations under quiescent conditions, a marked facility of the crystallization process was observed in the formation of stirrer-crystallized and Ziegler-Natta polystyrene. The ease of cryst...
TL;DR: In this paper, the results of an investigation on the orientation distribution of crystallites in polyethylene films having different degrees of orientation and fiber symmetry were described and, from visual inspection of the intensity of the 002 reflection, a qualitative comparison with the mechanical data was made.
Abstract: In an earlier note [1], the results of an investigation on the orientation distribution of crystallites in polyethylene films having different degrees of orientation and fiber symmetry were described and, from visual inspection of the intensity of the 002 reflection, a qualitative comparison with the mechanical data was made. Quantitative measurements of intensity distribution have now been made and from these the orientation distribution of crystallites and their effect on mechanical anisotropy have been evaluated.
TL;DR: The relative merits of time-temperature superposition procedures (those of Leaderman, Tobolsky, Ferry, Kě, McCrum, and Morris) have been assessed for the glass-rubber relaxation of an epoxy resin this article.
Abstract: The relative merits of time-temperature superposition procedures (those of Leaderman, Tobolsky, Ferry, Kě, McCrum, and Morris) have been assessed for the glass-rubber (a) relaxation of an epoxy resin. Measurements of creep compliance in shear were made at temperatures between 24° and 190°C. The different superposition procedures yield shift factor versus temperature plots which are essentially identical. Differences between the procedures are greatest in the master curves particularly at short and at long times. The McCrum-Morris procedure alone yielded a smooth master curve at all times. At temperatures above the glass transition the shift factor versus temperature plots followed the WLF equation.
TL;DR: In this article, the melting behavior of poly(ethylene oxide) fibrillar crystals was compared and the results discussed in relation to their respective morphologies, and it was shown that fibrilar crystals exhibited superheating which increased with the temperature of crystallization.
Abstract: Poly(ethylene oxide) fibrillar crystals were prepared from ethyl alcohol solutions by stirred crystallization in the temperature range 31°-37°C. Electron microscopy and calorimetric measurements show that the crystals consist of a central thread with extended chains and lamellar overgrowths with folded chains. The melting behavior of crystals prepared at the same temperature with stirring (fibrillar) and without stirring (lamellar) was compared and the results discussed in relation to their respective morphologies. The fibrillar crystals exhibited superheating which increased with the temperature of crystallization. This is related to the amount of material which crystallizes in the extended-chain central threads. The relatively narrow temperature range in which the fibrillar crystals form is related to the greater tendency of the highly flexible poly(ethylene oxide) chains to crystallize in the folded conformation. Molecular fractionation occurs during crystallization, and the plot of molecular ...
TL;DR: In this paper, a stress-relaxation measurement was conducted over the temperature range 15°-105°C on mats of single crystals of two linear polyethylene fractions, which were grown isothermally at several different temperatures.
Abstract: Stress-relaxation measurements have been conducted over the temperature range 15°–105°C on mats of single crystals of two linear polyethylene fractions. The single crystals were grown isothermally at several different temperatures. The relaxation modulus was observed to be strain dependent, indicating that the single crystal mats exhibited nonlinearity. In spite of this appearance of nonlinearity, it was found possible, when the relaxation modulus was extrapolated to zero strain by an appropriate method, to obtain correct relaxation spectra for the mats of single crystals prepared by isothermal crystallization. This spectrum was then used to calculate the dynamic viscoelastic functions and, for the unannealed sample crystallized at 80°C, good agreement was found between experimental results and calculated ones. Two annealed samples showed multiple absorptions and, under these circumstances, strict application of the method of reduced variables for time and temperature was impractical. The effect ...