The degree of crystallinity of monoclinic isotactic poly(propylene)

Isasi, José Ramón; Mandelkern, L.; Galante, Maria Jose; Alamo, Rufina G.

doi:10.1002/(sici)1099-0488(19990215)37:4<323::aid-polb6>3.0.co;2-3

Cited by 103 publications

(78 citation statements)

References 56 publications

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“…Even in conventional polyolefins such as polypropylene, the nature of the amorphous phase is not entirely understood, as evidenced by unresolved differences between the crystallinity measured by the density and the crystallinity measured by the heat of melting. 68 Various examples in this review illustrate how the transport of small gas molecules senses the permeable amorphous structure and probes the free volume of the disordered phase. This level of understanding has special practical importance for polyolefins for which environmental control is a key property in many packaging applications.…”

Section: New Opportunities For Gas Transport As a Structure Probementioning

confidence: 99%

Oxygen transport as a solid‐state structure probe for polymeric materials: A review

Hiltner

Liu

et al. 2005

J Polym Sci B Polym Phys

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ABSTRACT:In the quest to elucidate the solid-state structures of polymers, insight into the amorphous phase is particularly elusive. Although the permeability of small molecules is often measured as an important performance property, numerous researchers have found that a deeper analysis of the transport characteristics provides insight into polymer morphology, especially if used in combination with more usual characterization techniques. The transport of small gas molecules senses the permeable amorphous structure and probes the nature of the free volume. In recent years, our interest in the gas barrier of polyesters has resulted in an unusual opportunity to investigate the nature of the free volume in the polymer glassy state. This effort has been aided by access to aromatic polyesters with designed variations in their chemical structure. This review focuses on oxygen transport, supplemented with other methods of physical analysis, as a probe of the excess-hole free volume. The review addresses the profound effects of orientation and crystallization on the free volume of the glassy state. The discussion also presents a simple odel for the gas permeability of the isotropic glass based on lattice concepts and tests more sophisticated models for the gas permeability of semicrystalline polymers. The final section addresses other opportunities for fruitful applications of oxygen transport as a solid-state structure probe.

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Section: New Opportunities For Gas Transport As a Structure Probementioning

confidence: 99%

Oxygen transport as a solid‐state structure probe for polymeric materials: A review

Hiltner

Liu

et al. 2005

J Polym Sci B Polym Phys

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“…Temperature ranged from −45 • C to 200 • C and the heating/cooling rate was 20 • C min −1 . For crystallinity determinations, values of 290 and 209 J g −1 were taken as enthalpy of fusion of perfectly crystalline material in LDPE 14 and polypropylene, 15 respectively. Viscoelastic properties were measured with a Polymer Laboratories MK II dynamic mechanical thermal analyzer in the tensile mode.…”

Section: Techniquesmentioning

confidence: 99%

Structural Characterization and Relaxation Processes of the Inner Crystalline Core in Foams Based on Polyethylene/Polypropylene Blends

Benavente

Pereña

Pérez

et al. 2003

Polym J

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ABSTRACT:Injected foams obtained from blends with different compositions of isotactic polypropylene, iPP, and two different low density polyethylenes, LDPE, were analyzed by X-Ray diffraction, differential scanning calorimetry, and dynamic mechanical thermal analysis. Most of the results on the blends can be simulated as a weighed addition of the two pure components, indicating practical immiscibility. Some features about the crystallization of the iPP component pointed out inhibition and, consequently, a delay in the development of monoclinic crystalline entities.KEY WORDS Injected Foams / Polyethylene / Polypropylene / Immiscible Blends / Crystallization / Isotactic polypropylene, iPP, exhibits valuable properties and a very competitive price. Thus, this polymer is one of the most worldwide used commodity plastics. However, its poor low-temperature fracture toughness is a drawback so that it is often blended with elastomeric polymeric materials which improve very effectively the impact resistance of iPP (of course with some reduction of the modulus and strength). These iPP/elastomer systems are generally multiphasic, and optimum impact resistance is achieved by the proper particle size distribution of the dispersed (elastomeric) phase. 1 Accordingly, blends of iPP with poly(ethyleneco-propylene) (EPR), ethylene-propylene-diene terpolymer rubber (EPDM), poly(styrene-co-butadieneco-styrene) (SBS) and poly(ethylene-co-vinyl acetate) (EVA) have been extensively analyzed and several mechanisms of impact toughening have been proposed. [1][2][3][4][5] The constituents of a blend and respective content are not unique variables for determining specific properties but the type of processing technique used has significant influence. Therefore, behavior of injection molded structural foams that show a sandwich-like architecture consisting of a cellular core surrounded by a relatively solid integral skin 6-13 does not have to be the same possessed by material obtained by compression molding since the morphological details developed might be rather different. Moreover, the formation of a sandwich-like structure depends upon processing conditions and techniques used. The gas-counter process by egression of foamed melt from the core of the molding is an attractive method for manufacturing structural foams. Gas-counter pressure controls skin thickness, density and structure of the cellular core which is affected by the amount of the polymer melt egressed. 6,7,9 Variation of distinct parameters during processing promotes the resulting structure derived within the skin or core. Therefore, two layers are observed in unfoamed skin: an outer amorphous layer and an inner one that is crystalline. Increase in the spherulites size is gradually observed. 10 Consequently, the crystalline core and spherulites are the largest in the foamed core. This more perfect crystalline structure is probably due to low heat conductivity caused by the gas-phase that keeps the temperature almost constant long enough for the growth of foamed spherulites....

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“…For crystallinity determinations, a value of 209 J g −1 has been taken as the enthalpy of fusion of the perfect α modification of iPP. 39 Viscoelastic properties were measured with a Polymer Laboratories MK II dynamic mechanical thermal analyzer, working in a tensile mode. The temperature dependence of the storage modulus, E , loss modulus, E , and loss tangent, tan δ, was measured at 1, 3, 10, and 30 Hz over a temperature range from −150 to 150 • C at a heating rate of 1.5 • C min −1 .…”

Section: Methodsmentioning

confidence: 99%

“…The effect of the thermal history on its location has been reported for iPP. 39 A shift to higher temperatures is observed as crystallinity and crystal size increase. This tendency is altered for CPEQCO2.…”

Section: Viscoelastic Behaviormentioning

confidence: 98%

“…The β iPP process has been identified with the mechanism associated to the glass transition temperature of the amorphous regions within iPP blocks similarly to the relaxation appearing at the same temperature range in iPP homopolymers. 39 Similarly to the γ EPR relaxation, the effect of thermal treatment on this process is significant and its maximum is moved to higher temperatures as crystallinity and crystallite size are diminished. Larger crystallites seem to impose less motion restrictions to the cooperative motion along iPP amorphous phase, as reported in Table IV.…”

Section: Viscoelastic Behaviormentioning

confidence: 99%

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Structure and Mechanical Behavior of the Mesomorphic Form in a Propylene-b-Poly(ethylene-co-propylene) Copolymer and Its Comparison with Other Thermal Treatments

Arranz-Andrés

Benavente

Pérez

et al. 2003

Polym J

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ABSTRACT:Several thermal treatments have been imposed along processing to a poly[propylene-b-(ethylene-copropylene)] and their effect on structure, thermal characterization and mechanical response has been explored. Quenching in a dry ice/methanol bath after melting has allowed to obtain a mesomorphic form due to the existence of long isotactic polypropylene (iPP) chains within the block copolymer here studied. An exhaustive analysis of such a mesophase has been performed comparing its morphological details and mechanical properties with the rest of thermal treatments. A microspherulitic superstructure is found in this mesomorphic form which leads to the lowest values in mechanical parameters, such as storage and Young moduli as well as microhardness, compared to those exhibited by the other specimens with distinct thermal histories. However, the ductility of the mesomorphic structure is the highest one, owed to the non-existence of monoclinic crystallites. A phase transition is observed at around 90• C on heating, which suggests the transformation of this mesomorphic form to the monoclinic crystalline structure. KEY WORDS Poly(ethylene-co-propylene) / Mesomorphic Form / Monoclinic Crystallites /The crystallization behavior of isotactic polypropylene (iPP) is very complicated. The morphology and properties after crystallization depend upon thermal history and the detailed microstrucutre of the polymer molecules. The iPP chains adopt a 3 1 helical conformation when crystallized from the molten state. These helical chains can organize into several different spatial arrangements giving rise to three distinct polymorphs: α-monoclinic, β-hexagonal, and γ-orthorhombic forms, depending on the crystallization conditions and catalyst used. [1][2][3][4][5][6][7][8][9][10][11][12][13] Cooling from the melt at low or moderate cooling rates leads usually to the formation of the thermodynamically stable α-monoclinic crystalline lattice, being this α-form the most common one.Moreover, there is also a "mesomorphic" phase, which can be obtained by rapid quenching of molten iPP. The appearance of two broad peaks in the X-ray diffraction pattern is a characteristic of this quenched form. 14 The presence of broad, diffuse peaks in X-ray diffraction tends to suggest that the quenched structure is in a disorder state. These two peaks, however, exhibit an intermediate width between the crystal diffractions and the pattern found for a completely amorphous polypropylene. 15 Natta and Corradini 1 first pointed out that this form had an intermediate degree of ordering between the amorphous phase and the crystalline phase. They categorized it as smectic to indicate the presence of two-dimensional ordering, being better in longitudinal than in transverse chain direction. 16 However, the full evidence for the smectic phase in iPP has not been documented. The description of the mesophase can be quite confusing in the literature. In addition to the smectic phase, 1, 17 other investigators described the mesomorphic phase as paracrystalline, 18...

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The degree of crystallinity of monoclinic isotactic poly(propylene)

Cited by 103 publications

References 56 publications

Oxygen transport as a solid‐state structure probe for polymeric materials: A review

Oxygen transport as a solid‐state structure probe for polymeric materials: A review

Structural Characterization and Relaxation Processes of the Inner Crystalline Core in Foams Based on Polyethylene/Polypropylene Blends

Structure and Mechanical Behavior of the Mesomorphic Form in a Propylene-b-Poly(ethylene-co-propylene) Copolymer and Its Comparison with Other Thermal Treatments

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