摘要:

Polymer morphology has a unique role in macromolecular science. Because it deals primarily with images of microstructure, revealing actual organization in its inherent complexity rather than as oversimplified models, it provides a special wealth of information from which to draw inferences on molecular and other mechanisms involved in its formation and on the consequences for properties. The essential first step is to image the microstructure to allow the eye-brain combination to use its outstanding ability to interpret complex textural patterns. Not only have continual gains in fundamental understanding stemmed from corresponding advances in our ability to reveal and study morphology but so have insights leading to improved properties. These themes are illustrated with recent results for both pure and applied topics. The origin of spherulitic growth, the principal determinant of texture and thus properties in polymers, is a long-standing, sometimes controversial, issue. Now study of an academic system, monodisperse paraffins, has clearly negated the long-standing hypothesis of the responsibility of “impurities” in the melt. It also strongly supports previous suggestions that the essential cause is divergence of adjacent dominant lamellae from their branch points, due to the pressure of uncrystallized molecular cilia. The value of morphological studies in the development of commercial materials is illustrated, firstly, for advanced polyethylene fibers, both compacted and individual, in which novel longitudinal defects have been discovered, and then by details of impact-related failure in polypropylene copolymers.

ISSN:0022-2348    

DOI:10.1080/00222349608220381

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A mathematical model for the description of the overall crystallization of polymers has been developed which separates the pure geometric spreading of the semicrystalline superstructures from the increasing crystallinity inside these entities. The model uses the Avrami theory for the geometric part and a freely optional function for the increasing local crystallinity. The two functions are combined by a mathematical procedure calledconvolution. The free option of the local crystallinity function enables this model to permit calculation of this function, which is not accessible to direct measurement. Thus with given Avrami parameters and measured values of the time-dependent overall crystallinity, this function of the local crystallinity (secondary crystallization function) can be calculated. The model has been applied to test data produced by computer simulations.

ISSN:0022-2348    

DOI:10.1080/00222349608220382

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The phase diagrams of the binary systems poly(ethylene oxide) (PEO)-resorcinol and poly(ethylene oxide)-p-nitrophenol show the presence of molecular complexes with well-defined stoichiometries. The crystal structure of these two molecular complexes has been determined from wide-angle x-ray diffraction patterns of stretched films and spherulites. The morphology of the two complexes crystallized from the melt is investigated by differential scanning calorimetry and small-angle x-ray scattering. The crystallization of the PEO-resorcinol complex from the melt gives integral-folded crystals with either extended chains (EC) orn-folded chains (n-FC). As observed for PEO oligomers, the fraction of EC crystals of the PEO-resorcinol complex increases with the crystallization temperature to give finally only EC crystals but in a larger range of crystallization temperatures than for pure PEO. On the other hand, the PEO-p-nitrophenol complex crystallizes over all the studied crystallization range as stable nonintegral-folded (NIF) crystals. Two proposals related to the crystal structure of these complexes and their mode of growth are invoked to explain these two greatly different morphologies at the lamellar level.

ISSN:0022-2348    

DOI:10.1080/00222349608220383

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Techniques of electron microscopy and specimen preparation of polymers for studying morphology and interfacial layers are briefly reviewed, including a discussion of general problems of electron microscopic investigations of polymers arising from irradiation sensitivity and low contrast. To improve contrast, some irradiation-induced effects are applied to reveal arrangement of lamellae and intralamellar defects in semicrystalline polymers (polyurethane — PU and polyethylene — PE). Structure formation has been studied in PE using a special technique of irradiation-induced fixation in the melting range. Using this technique, structure formation processes in polymer blends [e.g., low-density PE/high-density PE (LDPE/HDPE) blends] can also be studied. Using in situ deformation tests in the electron microscope, strength of interfaces is determined in several polymer combinations. As a consequence, the structural details which are important for mechanical properties can be defined.

ISSN:0022-2348    

DOI:10.1080/00222349608220384

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Rheo-optical methods are briefly reviewed. Light-scattering techniques have been chosen as a case. A hypothesis concerning the breakup of layer samples was tested by comparing with data obtained by rheo-optical measurements and electron microscopy. The samples were made by sandwiching a thin PS film between two plaques of PMMA sheets making up a disk. The sandwich sample was run at various shear rates in a parallel plate glass geometry in a rheo-optical setup built into a Rheometrics mechanical spectrometer. The time dependence of the breakup process was evaluated from the light-scattering measurements and sustained by micrographs recorded at selected points. The stability time was determined as the time between inception of shear and the point at which the sample scattered light. At low shear rates a high scattering of stability time was observed which was believed to be dominated by imperfections in the interfacial region. A film breakup mechanism involving creation of parallel layers of thin, filmlike formations parallel with the original film is observed. These “layers” then break up to a final state encompassing nearly spherical drops spread over a thickness much larger (by orders of magnitude) than the original film thickness.

ISSN:0022-2348    

DOI:10.1080/00222349608220385

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The morphology of nascent poly (p-oxybenzoate/2,6-oxynaph-thoate) copolymers of 3/1, 1/1, and 1/3 mole ratio composition, prepared by bulk solution and confined thin film melt and solution polymerization (CTFMP, CTFSP), is described. While the bulk solution polymerization (at 300°C in heat transfer fluids) yields only spherical aggregates of smaller spheres, both CTFMP and CTFSP yield lamellar crystals suitable for electron diffraction (ED);hk0patterns are obtained resembling those from the homopolymers. Shearing of the solution-polymerized material permits obtaining ED fiber patterns; as expected nonperiodic c-axis reflections are obtained, the 002 spacing corresponding to that observed by x ray for the same compositions. The effect of annealing nearTk-misexamined using differential scanning calorimetry (DSC) and ED. In thicker CTFMP films a superlattice structure is observed. It is apparently composed of ribbons on edge, of uniform width and thickness, with step changes in the width and, in some cases, a periodic structure (in phase from ribbon to adjacent ribbon) along their length. The periodicities in the three directions are on the order of 1000 Å. Limited evidence suggests they grow from a basal lamella, with the molecules normal to the substrate and parallel to the width of the ribbon.

ISSN:0022-2348    

DOI:10.1080/00222349608220386

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Morphology of polyethylene spherulites has been investigated by the low-dose technique using transmission electron microscopy (TEM) in a scanning mode for dark field and microdiffraction. Specimens were prepared by solvent casting and subsequent recrystallization at different temperatures. The dark-field studies provide spatial information on the lamellar morphology. Two major types of spherulite morphology have been observed: At high temperatures (low crystallization rate) the dark fields show a preferred orientation of the lamellae along the 020 axis. At low temperatures the preferred orientation is 110. The microdiffraction patterns confirm the dark-field results and also show that for intermediate temperatures, regular alteration of regions with 020 and 110 growth planes is responsible for the ringed spherulite appearance. The twisted lamellae model cannot be excluded, but it is shown that it is not responsible for the regular changes in contrast. A model of dendritic growth of spherulite lamellae is used in which the plane of crystal growth is temperature dependent and, for intermediate temperatures, results in regular fluctuation in the mode of crystal growth, branching, and ringed spherulites appearance.

ISSN:0022-2348    

DOI:10.1080/00222349608220387

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Due to the practical problems connected with polymer morphology, in both process viability and product processability, the morphology of the catalyst-polymer particle in a heterogeneous polymerization has been the object of great scientific effort at Montecatini and its successor since 1968. A model for the polymer growth mechanism, elaborated at the Ferrara laboratories in the late 1960s, was experimentally proven in the following years and has been adopted for the development of novel catalysts/processes/materials. More recently, thanks to the implementation of the fourth-generation catalyst system and its “reactor granule technology” approach, Montell has been able to produce novel polyolefin-based materials in spherical form with the broadest property ranges. In addition, the spherical-form polymers are utilizable without any pelletization operation, avoiding the related costs and improving polymer final quality. This paper describes the development and characterization of these polymers.

ISSN:0022-2348    

DOI:10.1080/00222349608220388

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The paper discusses the influence of an amorphous oligomer (namely hydrogenated oligocyclopentadiene — HOCP) on the morphology and the phase structure of its blends with several polyolefins as a function of composition and crystallization conditions. In particular the following polyolefins were studied: high-density polyethylene (HDPE), isotactic polypropylene (IPP), poly(l-butene) (PB-1), and poly(4-methyl pentene-1) (P4MP1). The blends under investigation are complex polymer systems. In fact, in dependence on temperature, blend composition, and cooling rate, they assume different morphologies and consequently show different thermal and mechanical behaviors. In the solid state the blends form a generally three-phase system: a crystalline phase of polyolefin and two amorphous phases, one rich in the amorphous polyolefin and the other in HOCP. The crystallization process and the properties are determined by the morphology and the phase structure, as well as by the physical state of the HOCP-rich phase.

ISSN:0022-2348    

DOI:10.1080/00222349608220389

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The efficiency of structurally different copolymers as compatibilizers for the homopolymer blend PVC/PS (polyvinylchloride/polystyrene) was tested. As expected, a diblock copolymer SbMMA of styrene and methylmethacrylate, with a MMA block twice as long as the styrene block, did well, refining the phase morphology of PVC/PS drastically. But a random copolymer ScoMMA with the same monomer composition was efficient as well. Particularly interesting are block-graft copolymers made by grafting MMA or a random copolymer CHMAcoMA (CHMA: cyclohexylmethacrylate, MA: methylacrylate) onto a diblock copolymer SbB of styrene and butadiene. With these block-graft copolymers, a mechanism of compatibilization in two stages was observed that leads to finer phase structures than theoretically expected.

ISSN:0022-2348    

DOI:10.1080/00222349608220390

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor