Electron microscopy study of the structure of normal and abnormal poly(butylene terephthalate) spherulites

Normal and abnormal spherulites of polybutylene terephthalate cast from solution in HFIP were investigated by electron microscopy (CTEM and STEM). Both spherulite types crystallize in the α form. The crystallite is biaxial with its greatest polarizability directions Z and Y oriented along the molecular chain and perpendicular to it in the plane of the terephthalate residue. In the normal spherulites, the [2 10]^* direction is parallel to the radius direction, so that both Z and Y directions are oriented tangentially (negative spherulites). In the abnormal spherulites, the [1 11]^* direction is parallel to the radius, and this explains the observed abnormal light scattering pattern.     

Quiescent and strain-induced crystallization of poly(p-phenylene terephthalamide) from sulfuric acid solution

Quiescent and strain-induced crystallization of poly(p-phenylene terephthalamide) (PPTA) from sulfuric acid solution has been studied. Negative spherulites (SA-PPTA spherulites) are formed from hot concentrated solutions by cooling. The spherulite consists of radiating fibrous lamellae several hundred angstroms wide. The electron diffraction pattern indicates that PPTA molecules are oriented perpendicular to the long axes of the fibrous lamellae and that the [010] or [110] direction of the modification I crystal and [010] direction of the modification II crystal are parallel to the long axes of the fibrous lamellae. The width of the lamellae is much smaller than the chain length of the starting PPTA. It appears that hydrolysis of PPTA during melting crystallization determines the chain length, i.e., the width of the fibrous lamella. Stacked, lamellar structures like “row structures” are formed under shear. The longer axes of the fibrous lamellae are oriented perpendicular to the shear direction. It is confirmed by electron diffraction studies that the PPTA molecules are oriented parallel to the shear direction. Well-developed fibrils with the PPTA molecules oriented to the fibril axis, are formed by adding the SA-PPTA spherulites to water with vigorous stirring.     

Morphological studies on polybutylene terephthalate

The morphology of poly(butylene terephthalate) (PBT) crystallized from the melt at various temperatures was studied by small-angle light scattering, polarizing microscopy, and wide-angle x-ray diffraction. Spherulites with a maltese cross at 45° to the polars formed at lower temperatures while spherulites having an apparently higher melting point with a maltese cross along the polars (0°–90°) formed at higher temperatures. The spherulite size and crystallinity increased with increasing crystallization temperature. The H_v scattering patterns arising from the spherulites formed at lower temperature showed intensity maxima at azimuthal angles of 0° and 90°, while those obtained at higher temperatures showed the more common 45° intensity maxima. Microtomed samples from molded PBT bars showed spherulites with a 45° maltese cross which changed to a 0°–90° maltese cross upon heating just prior to melting. The skin-core effect due to varying thermal histories in these molded bars was clearly observed. Solvent crystallized films contained positive 0°–90° spherulites. Some changes occurring upon uniaxial stretching of PBT films are also discussed.     

Small-angle light scattering from a distribution of spherulite sizes

Depolarized small-angle light scattering from spherulites in semicrystalline polymers gives rise to a characteristic cloverleaf pattern. For scattering from a single spherulite, the position of the maximum in scattered intensity is readily related to the spherulite radius. For a distribution of spherulites, the maximum should be related to some characteristic measure of the distribution. It is shown for a wide variety of distributions that this characteristic radius is a ratio of high moments of the size distribution, specifically R* ≈ 〈R⁷〉/〈R⁶〉. The shape of the light-scattering profile should in principal be related to the nature of the spherulite distribution. Calculations of scattering profiles from a variety of distributions fail to demonstrate this, owing to the strong dependence of scattering power on spherulite size. Exceptions are noted for the case of certain bimodal distributions.     

聚环氧乙烷球晶的带状结构与球晶内部的环形裂纹

聚环氧乙烷球晶的带状结构与球晶内部的环形裂纹丁建东，朱军祥，杨玉良（复旦大学高分子科学系、国家教委聚合物分子工程开放实验室，上海，２００４３３）关键词聚合物，带状球晶，裂纹聚环氧乙烷（ＰＥＯ）具有高度的柔顺性，易于结晶，因而被人们选作研究聚合物结晶的...     

Lamellar assembly corresponding to transitions of positively to negatively birefringent spherulites in poly(ethylene adipate) with phenoxy

Surface morphology of positively or negatively birefringent spherulites in melt-crystallized neat poly(ethylene adipate) (PEA) vs. PEA blend with phenoxy was examined using atomic force microscopy (AFM), scanning electron microscopy, polarizing optical microscopy, thermal analysis, and wide-angle X-ray techniques. Their top-surface morphology in thin film forms was analyzed to fully expounded the lamellar assembly responsible for the opposite birefringence. Top-surface lamellar assemblies in positive/negative types of ringless spherulites (T _c = 0, 15, 20, 40 °C) and also alternating birefringence of double-ring-banded spherulite (T _c = 28 °C) of PEA/phenoxy blend were examined with AFM. From the results, spherulite’s positive and negative birefringence differs only in interior lamellar arrangements but not lattice geometries. Negative spherulites are composed of radially oriented edge-on lamellae, while positive spherulites are composed of bending/coiling edge-on lamellae. By contrast, the ring-banded spherulites can exhibit both negative and positive birefringence depending on the alternating radial and tangential lamellar arrangement. The addition of phenoxy into PEA could disrupt the regular lamellar bending and promote the singularity of edge-on lamellae; owing to that, the amorphous phenoxy induces looser arrangement of edge-on lamellae with phenoxy being in interlamellar/interfibrillar regions. The bulky linking pendent group phenoxy, with H-bonding capacity interacting with PEA, also disrupts the regularity of tangential–radial PEA lamellae to display a more zigzag pattern.     

Microstructure and unit-cell orientation in α-polypropylene

The microstructure of melt-grown dendritic aggregates of the monoclinic α phase of isotactic polypropylene has been examined by optical microscopy, electron microscopy, and electron diffraction. Whereas the tightly crosshatched structure of such dendrites grown in the usual manner from the melt had not heretofore permitted unequivocal determination of unit-cell orientation, crystallization on mica at high temperatures eliminates this problem by suppressing branching and allowing lamellae to grow uninterruptedly to many micrometers in length. In this manner, it is shown that the preferred growth direction in single crystals of α-polypropylene is a^*. X-ray diffraction analysis of unidirectionally crystallized specimens shows that the a^* axis becomes radial in spherulites of this polymorph. Implications of this growth axis in terms of the branching model and of the crystallographic identification of the amorphous surfaces are discussed. Addition of large amounts of melt diluents is found to impart a distinct curvature to the dendritic crystals, causing their concave sides to face preferentially toward the centers of the resulting spherulitic aggregates.     

Crystalline texture of injection-molded nylon 6

Injection-molded specimens of nylon 6 were examined by x-ray diffraction as a function of depth in three characteristic directions. A skin and a core were always found to be present which differed in the degree of crystalline perfection and crystal modification. While the core of pure nylon 6 was found to be not oriented, the core of specimens containing nucleating agents was found to contain a typical texture of the monoclinic modification of nylon 6 in which the distribution probability of the a^* and c^* axes resembles ellipsoids with three unequal axes. A model explaining this texture as due to degenerated (deformed) spherulites is proposed. With a transcrystalline nylon 6 specimen the direction of the fastest growth in the unit cell (which forms the radius of spherulites) is found to be close to the a axis.     

Effect of poly(butylene succinate) crystals on spherulitic growth of poly(ethylene oxide) in binary blends of the two substances

The effects of the lamellar growth direction, extinction rings, and spherulitic boundaries of poly(butylene succinate) (PBSU) on the spherulitic growth of poly(ethylene oxide) (PEO) were investigated in miscible blends of the two crystalline polymers. In the crystallization process from a homogeneous melt, PBSU first developed volume‐filling spherulites, and then PEO spherulites nucleated and grew inside the PBSU spherulites. The lamellar growth direction of PEO was identical with that of PBSU even when the PBSU content was about 5 wt %. PEO, which intrinsically does not exhibit banded spherulites, showed apparent extinction rings inside the banded spherulites of PBSU. The growth rate of a PEO spherulite, G_PEO, was influenced not only by the blend composition and the crystallization temperature of PEO, but also by the growth direction with respect to PBSU lamellae, the boundaries of PBSU spherulites, and the crystallization temperature of PBSU, T_PBSU. The value of G_PEO first increased with decreasing T_PBSU when a PEO spherulite grew inside a single PBSU spherulite. Then, G_PEO decreased when T_PBSU was further decreased and a PEO spherulite grew through many tiny PBSU spherulites. This behavior was discussed based on the aforementioned factors affecting G_PEO. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 539–547, 2009     

聚对苯甲酰胺液晶态球晶生长机理

本文用热台偏光显微镜和透射电子显微镜研究了聚对苯甲酰胺(PBA)/H_2SO_4液晶态生长球晶的形态结构和结晶机理。结果表明,PBA/H_2SO_4向列型液晶相具有过冷状态,可达30—40℃左右,并可生长球晶结构,一般直径可达5毫米左右。20Wt％溶液在不同的过冷态结晶时,可以生成三种形态的球晶结构,这是由于构成球晶的基本结构单元——有序微区结构在不同过冷条件下堆砌排列的规整程度不同的缘故。球晶的形态结构只与过冷程度有关,而与溶液的浓度无关。同时还研究了变温和剪切应力下结晶的球晶形态。     

ATOMIC FORCE MICROSCOPY STUDIES OF POLYCAPROLACTONE RINGED SPHERULITES*

The surface morphology of free-surface PCL ringed spherulites was investigated by using atomic forcemicroscopy. The spherulites were obtained by crystallization of PCL/PVC blends of different compositions. It was found thatthe ringed spherulite exhibited regularly fluctuating rings on its surface. Compared with the bright-dark ring pattern of thespherulite under a polarizing microscope, it was proved that the optical characteristics of the ringed spherulite underpolarizing microscope coincided with its surface characteristics. The bright rings in polarizing micrographs of the spherulite coincided with the convex rings on its surface, while the dark rings coincided with the concave rings.     

Characterization of the structure and organization of β-form crystals in type III and type IV isotactic polypropylene spherulites

Anisotropic growth of β-form crystals of isotactic polypropylene in type III and type IV spherulites has made possible microanalysis of the unit cell structure, optical properties, and crystal arrangement within the spherulites. Micro x-ray studies of the type III and type IV spherulites show that interspherulitic β-form crystals have a hexagonal unit cell with dimensions; a = 19.08 Å and c = 6.49 Å. The intrinsic refractive indices of these β-form crystals are 1.506 along the a axis and 1.536 along the c axis. The organization of the crystals within the spherulites and the optical properties of the spherulites are also quantitatively evaluated. Both the type III and type IV spherulites have the a axis of the crystal radial while the crystals rotate randomly around the type III spherulite radii and periodically around the type IV spherulite radii. The radial refractive index for both the type III and type IV spherulites has the same value of 1.496. The tangential refractive index of the type III spherulite has a constant value of 1.509; it varies periodically between a minimum of 1.496 and a maximum of 1.519 in the type IV spherulite. Microtechniques such as micro x-ray diffraction, interference microscopy, birefringence, and optical microscopy were required for acquisition of the data.     

Morphologies and enzymatic degradability of melt-crystallized poly(3-hydroxybutyric acid-Co-6-hydroxyhexanoic acid)

The films of poly[(R)-3-hydroxybutyric acid-co-10mol% 6-hydroxy-hexanoic acid] (P[(R)-3HB-co-6HH]) were prepared by melt-crystallized method at various crystallization temperatures. The morphologies and properties of melt-crystallized films were characterized by means of x-ray diffraction, differential scanning calorimetry, optical microscopy, and scanning electron microscopy. All of the melt-crystallized films showed the banded spherulite morphology. The enzymatic degradation of melt-crystallized films was carried out at 37 °C in an aqueous solution (pH 7.4) of PHB depolymerase from Alcaligenes faecalis. The rate of enzymatic erosion was strongly dependent on the crystallinity of films, and the highest rate was as large as 2.15 mg·h⁻¹·cm⁻². After enzymatic degradation, the banded morphology of P[(R)-3HB-co-6HH] spherulites was visible, suggesting that PHB depolymerase predominantly hydrolyzes polymer chains on the edges of crystalline lamellar stacks.     

Crystalline morphology of a thermotropic aromatic polyester crystallized from nematic melt

The crystalline morphology of a thermotropic aromatic polyester crystallized from a nematic melt was investigtated by means of polarized optical microscopy (POM) and scanning electron microscopy (SEM). Due to POM measurements it was found that spherulites of two different types are formed within the two different temperature regions. When T_c was exceeding 170°C, spherulites of type‐1 showing a negative birefringence grew with a radial fibrillar morphology and exhibited a clear Maltese‐cross pattern. The radius growth rate of type‐1 spherulites was about 2.2 μm/min at 185°C. When T_c was smaller than 160°C, spherulites of type‐2 were formed and exhibited a radially outward growing structure but no evident Maltese‐cross pattern. These spherulites could be seen by the naked eyes due to their size reaching several millimeters. SEM observations revealed that the spherulites of type‐1 exhibited a ripple‐like homocentric morphology with periodical compact fibrils having a diameter of about 150 nm perpendicular to the radial direction. In contrast, the spherulites of type‐2 exhibited, as apparent from performed SEM images, radially growing crystallites of about 500 nm in size with no periodicity in the radial direction.     

Morphology and interpenetrated growth of spherulites in miscible poly(ethylene succinate)/poly(ethylene oxide) blends

Morphology development and growth process of spherulites in miscible poly(ethylene succinate)/poly(ethylene oxide) blends are studied by means of polarizing optical microscopy and atom force microscopy in this paper. Thin films with different film thicknesses were used to follow the growth processes of spherulites and dendrites. It is shown that, when one component spherulite grows, the other component in the melt is always excluded from the spherulite. The excluded component may reenter into the spherulite through diffusion depending on amorphous volume fraction of spherulite and segmental mobility of molecules, which leads to the occurrence of interpenetrated growth. This mechanism was analyzed in detail in this paper.     

Deformation of polybutene-1 spherulites

The deformation of fresh and aged polybutene-1 spherulitic samples has been investigated by microscopic observation, interferometry, studying macroscopic and spherulitic birefringence changes, and study of light-scattering patterns. The spherulite deformation is not affine, the microscopic deformation ratio being less than the macroscopic deformation ratio of the sample and greater in the equatorial regions of the spherulite than in the polar regions. The deviation from affine deformation is less for fresh spherulites than for the aged, where void formation occurs in the equatorial part of the spherulite. This gives rise to large scattering by this part of the spherulite and to form birefringence. The spherulite birefringence and its change with elongation is dependent upon the degree of aging of the sample. The spherulite birefringence is more negative for the aged sample. In the polar regions of the spherulite, this negative birefringence decreases and turns positive at higher elongations, characteristic of a reorientation of the crystals with their optic axes turning from being perpendicular to parallel to the spherulite radius. The spherulite birefringence in the equatorial direction becomes somewhat more negative on stretching a fresh sample but less negative on stretching an aged one. Spherulite distortion and orientation changes are apparent from the light-scattering patterns of films possessing small spherulites. The changes in V_v and H_v scattering patterns upon stretch are different for the fresh and aged samples. The V_v patterns of the fresh samples decrease in intensity with time after stretching a fresh sample with the H_v patterns do not.     

Structural studies on the polymorphism of nylon 3

The structure and morphology of crystalline nylon 3 [poly(β-alanine)] have been studied by electron microscopy and x-ray diffraction. Two clearly defined forms are detected. Form I appears as spherulites made up of ribbonlike lamellae upon crystallization at high temperature from a solution in phenol–butanediol-1,4. They have monoclinic unit cell with a = 9.60 Å, c = 8.96 Å, and β = 122.5°. The hydrogen-bonded planes run parallel to the long dimension of the crystals. Form II is observed when the samples are prepared from formic acid solution at room temperature. A second type of spherulite with a microfibrillar structure is formed in this case. The isolated crystalline structures obtained from Form II appear to grow along the intersheet direction rather than along the hydrogen bond direction, which constitutes anomalous behaviour. Our results for this second form are consistent with an orthorhombic lattice with a = 9.56 Å and c = 7.56 Å. No clear information is obtained on the b dimension of the unit cell (chain axis) in either case. We assume a value of 4.78 Å, which corresponds to fully extended chains. The two forms coexist in films prepared from a formic acid–water solution as well as in samples recovered immediately after polymerization.     

The effect of spherulitic truncation on small-angle light scattering

The effects of spherulitic truncation on the H_v small-angle light-scattering (SALS) patterns are determined by computer simulation of spherulite nucleation and growth. The simulation is carried out for simultaneous and sporadic nucleation of two-dimensional spherulites and simultaneous nucleation of three-dimensional spherulites. The scattered intensity differences between truncated spherulites and round spherulites are determined as functions of the type of growth and the volume (or area) fraction of spherulites. Methods for the determination of certain geometrical characteristics of spherulites systems by SALS are developed. These characteristics include the volume (or area). fraction of spherulites, the average spherulite radius, and the average spherulite volume (or area). The results of this study are essential in the quantitative analysis of H_v SALS from spherulitic systems. The simulation process is readily extendable to the examination of other morphological phenomena by SALS.     

Formation of new banded spherulites in polyimides

The crystalline morphology and structural development of aromatic polyimides during an optimum continuous thermal imidization procedure were examined by means of polarized optical microscopy and X‐ray diffraction. During thermal imidization, 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride/1,3‐diaminobenzene polyimide samples formed complicated spherulites, which, in addition to zigzag Maltese crosses, also showed concentric extinction rings, which are characteristic of banded spherulites. The factors affecting the formation of banded spherulites were studied. The initial imidization conditions dramatically affected the formation of the banded spherulite morphology: slow heating (0.5 °C/min) or fast heating (20 °C/min) led to relatively small polyimide spherulites and less identifiable extinction rings. The morphological features were also affected by the molecular weight of the polyimide: higher molecular weight samples showed typical banded spherulites, whereas low‐molecular‐weight samples formed degenerated banded spherulites. In all the spherulites formed in 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride/1,3‐diaminobenzene polyimides, special zigzag Maltese crosses, instead of normal Maltese crosses, were observed. The relationship between the imidization procedure and the spherulite morphology formation was also studied. X‐ray and Fourier transform infrared together revealed that after several minutes of thermal treatment, the crystallization was nearly complete, with a 42.5% degree of crystallinity; meanwhile, only some poly(amic acid) converted to the corresponding polyimide, with a 27% degree of imidization. The crystalline morphology and structure formed in the initial stage of the imidization process were maintained during the following imidization processing at an elevated temperature. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1997–2004, 2005     

Non‐Radial Growth of Helical Homopolymer Crystals: Breaking the Paradigm of the Polymer Spherulite Microstructure

Radial symmetry is essential for the conventional view of the polymer spherulite microstructure. Typically it is assumed that, in the course of the spherulite morphogenesis, the lamellar crystals grow radially. Using submicron X‐ray diffraction, it is shown that in banded spherulites of poly(propylene adipate) the crystals have the shape of a helix with flat‐on crystals winding around a virtual cylinder of about 6 µm in diameter. The helix angle of 30° implies that the crystal growth direction is tilted away from the spherulite radius by this angle. The implications of the helical crystal shape contradict the paradigm of the spherulitic microstructure. The radial growth rate of such spherulites does not correspond to the crystal growth rate, but to the propagation rate of the virtual cylinder the ribbons wind around.