The structure of the mesomorphic phase of quenched isotactic polypropylene

Caldas, V.; Brown, G. R.; Nohr, Ronald S.; MacDonald, John; Raboin, Louis

doi:10.1016/0032-3861(94)90931-8

Cited by 82 publications

(87 citation statements)

References 32 publications

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“…7,16,17,21 Caldas et al investigated the relationship between the crystalline form and the intensity ratio of doublet, and established the origin of different intensity ratio for the lower crystalline order form (α 1 ) with C2/c and the higher crystalline order form (α 2 ) with P2 1 /c space group. [16][17][18] Two different environments giving doublet exist in the crystal cell depending on the arrangement of left-and right-handed helices at the interlayer region.A gelation as well as crystallization is another recent topic. Generally the gelation accompanies the formation of three dimensional network structure consisted of crystalline as a cross-linking point.…”

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“…There is also a mesomorphic structure which can be obtained by quenching from the melt. The investigation of this form has been performed by lots of researchers, who proposed the interpretations such as smectic phase, 2 paracrystal, 13, 14 microcrystallite, [15][16][17][18] and so on. The recent study seems to reach the conclusion that the ordered helical chain distributes without longitudinal order, however the crystalline unit is close to the structure of the monoclinic α-form.…”

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Molecular Structure of Isotactic Polypropylene Formed from Homogeneous Solution. Gelation and Crystallization

Nakaoki

Inaji

2002

Polym J

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ABSTRACT:The molecular structure and morphology grown from isotactic polypropylene (iPP)/o-dichlorobenzene solution were investigated by thermal analysis and high-resolution solid-state 13 C NMR. The morphology varied depending on incubated temperature. A gelation occurred below 70• C, while the crystallization took place over 80• C. The crystal obtained was identified with the α-form, which is the most stable crystalline modification of iPP. In CP/MAS 13 C NMR spectrum, the chemical shift of methylene, methine, and methyl carbons provided almost the same shift for both the gel and α-form, but the characteristic doublet for methylene and methyl signals of the gel was different in intensity ratio with the α-form. These results indicate that the gel-forming crystal is identified with α 1 -form, being the disordered α-form. Indeed, the lower melting temperature and smaller melting enthalpy than the crystal were observed by thermal analysis. This result connects to the incompleteness of crystal formed in the gel.KEY WORDS Isotactic Polypropylene / Gelation / Crystallization / Morphology / Thermal Analysis / Solid-State 13 C Nuclear Magnetic Resonance (NMR) /Isotactic polypropylene (iPP) shows polymorphs as a function of crystallization condition. As for the molecular conformation, all crystal modifications take a regular trans-gauche (tg) conformation with 3/1 helix. The most thermodynamically stable form takes a monoclinic structure called α-form. 1 The pseudohexagonal β-form is obtained by high cooling rate or by adding specific nucleating agents. 2-8 The orthorhombic γ-form has unique chain structure which is featured by nonparallel chain axes to one another. [8][9][10][11][12] This form can be obtained by crystallization for low molecular weight iPP or by dealing at high pressure. There is also a mesomorphic structure which can be obtained by quenching from the melt. The investigation of this form has been performed by lots of researchers, who proposed the interpretations such as smectic phase, 2 paracrystal, 13, 14 microcrystallite, [15][16][17][18] and so on. The recent study seems to reach the conclusion that the ordered helical chain distributes without longitudinal order, however the crystalline unit is close to the structure of the monoclinic α-form. 19 In order to investigate these crystalline modifications, high-resolution solid-state 13 C NMR is a powerful tool. First Bunn et al. reported the characteristic doublet with 2 : 1 intensity ratio for methylene and methyl signals in cross polarization (CP) / magic angle spinning (MAS) 13 C NMR. 20 After that, lots of investigations using high-resolution solid-state 13 C NMR were carried out. 7,16,17,21 Caldas et al. investigated the relationship between the crystalline form and the intensity ratio of doublet, and established the origin of different intensity ratio for the lower crystalline order form (α 1 ) with C2/c and the higher crystalline order form (α 2 ) with P2 1 /c space group. [16][17][18] Two different environments giving doublet exist in the cryst...

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Molecular Structure of Isotactic Polypropylene Formed from Homogeneous Solution. Gelation and Crystallization

Nakaoki

Inaji

2002

Polym J

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“…The method used to microtome the iPP fibers was the same as that described previously for the talline morphology of the iPP fibers and spunbonded fabrics was performed as described previously for the quench-cooled films. 20 noted, with some indication of primary particles dispersed throughout the silicone copolymer. In addition, the bundles of particles that are observed in certain regions are consistent in size…”

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confidence: 93%

Enhancement of tensile properties of isotactic polypropylene spunbonded fabrics by a surface-modified silica/silicone copolymer additive

Caldas

Brown

Nohr

et al. 1997

J. Appl. Polym. Sci.

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Previous work at Kimberly -Clark Corp. (R. S. Nohr and J. G. MacDonald, Kimberly -Clark Corp., unpublished results, 1990 ) demonstrated that the addition of an ultrafine-particle ( submicron-size), surface-modified silica predispersed in an alkyl silicone to isotactic polypropylene (iPP) results in dramatic improvements in the tensile properties of fibers and spunbonded fabrics. For both fibers and spunbonded fabrics prepared with a high concentration of the low melt flow index (MFI) resin the incorporation of the additive resulted in markedly improved tensile properties. In this article it is shown that under quiescent conditions the surface-modified silica/silicone copolymer additive acts as an effective nucleating agent for iPP. This results in a reduction in the size of the crystalline entities, hence a more homogeneously distributed crystalline phase and load-bearing ''tie'' molecules. Indeed, scanning transmittance electron microscopy (STEM ) studies show that the crystalline entities are substantially smaller at the surface and mid-radius of fibers prepared with additive containing iPP. Furthermore, the bond points of the resulting spunbonded fabrics have a dramatically increased nucleation density and smaller crystallite dimensions.

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“…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, 18,19 microcrystallites, [20][21][22][23] and nano-crystallites. 24 The term conformationally disordered crystal (condis crystal) 25 has been suggested to be more appropriate for the iPP mesomorphic form, based on its frozen liquid-like structure.…”

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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 structure of the mesomorphic phase of quenched isotactic polypropylene

Cited by 82 publications

References 32 publications

Molecular Structure of Isotactic Polypropylene Formed from Homogeneous Solution. Gelation and Crystallization

Molecular Structure of Isotactic Polypropylene Formed from Homogeneous Solution. Gelation and Crystallization

Enhancement of tensile properties of isotactic polypropylene spunbonded fabrics by a surface-modified silica/silicone copolymer additive

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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