Isotacticity effect on crystallization and melting in polypropylene fractions: 1. Crystalline structures and thermodynamic property changes

Cheng, Stephen Z. D.; Janimak, James J.; Zhang, Anqiu; Hsieh, Eric T.

doi:10.1016/0032-3861(91)90477-z

Cited by 162 publications

(143 citation statements)

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“…There are several works addressing the chemical effects with regard to the lamellar thickness of semi-crystalline polymers. 40,41 Cheng et al 40 investigated the effects of stereoregularity (/mmmmS¼78-99%) on the /lS of iPP at various T c s. We replotted their results in addition to a recent result on the /lS of iPP 19 over a wide temperature range in Figure 6b. The low isotacticity samples show thinner lamellar thickness than do those of high isotacticity.…”

Section: Mobility Effects On Lamellar Thicknessmentioning

confidence: 99%

Critical roles of molecular dynamics in the superior mechanical properties of isotactic-poly(1-butene) elucidated by solid-state NMR

Miyoshi

Mamun

2011

Polym J

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Isotactic-poly(1-butene) (iPB1) shows superior mechanical properties after crystal-crystal transitions. Recently, Miyoshi et al. found that crystalline stems in metastable tetragonal crystal perform uniaxial rotational diffusions accompanying side-chain conformational transitions in the fast motional limit (correlation time, /s c S o10 À7 s; Macromolecules 2010, 43, 3986-3989.). In this study, molecular dynamics in stable trigonal crystal is investigated by solid-state nuclear magnetic resonance, which indicates that crystalline stems and side-chain conformations are completely fixed up to melting points (/s c S 410 s). In addition, lamellar thickness, /lS of iPB1 and a low isotacticity iPB1 (low_iPB1) with /mmmmS¼78%, respectively, were investigated by small-angle X-ray scattering. The low_iPB1 sample shows very week supercooling dependence of /lS (B5 nm), whereas iPB1 shows strong supercooling dependence of /lS (10-28 nm). On the basis of molecular dynamics and /lS results, molecular dynamics effects on structures and unique mechanical property of iPB1 are discussed.

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Section: Mobility Effects On Lamellar Thicknessmentioning

confidence: 99%

Critical roles of molecular dynamics in the superior mechanical properties of isotactic-poly(1-butene) elucidated by solid-state NMR

Miyoshi

Mamun

2011

Polym J

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“…An increase in crystallinity can lead to an increase in the lamellar thickness which leads to higher storage modulus and stiffiness values [2][3][4] . The effects of molecular weight [5][6][7][8] , molecular weight distribution [9] and tacticity [10][11][12][13] on the crystallization have been investigated by several authors. Cheng et al [6] showed that the linear growth rate of crystals decreases with the increase of molecular weight, but the overall crystallization rate might increase because an increasing number of intramolecular folded-chain nuclei could result in a higher nucleation density [7] .…”

Section: Introductionmentioning

confidence: 99%

Molecular weight and tacticity effect on morphological and mechanical properties of Ziegler–Natta catalyzed isotactic polypropylenes

2015

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SbstractThe morphological and mechanical properties of Ziegler-Natta catalyzed isotactic polypropylenes as influenced by the molecular weight and tacticity was investigated. Polypropylene samples were injection moulded into standard disks with a HAAKE MiniJet II injection moulder at 190 °C and 200 bar for morphological and mechanical tests. The morphological and mechanical properties of specimens were investigated by means of optical microscope (OM), scanning electron microscopy (SEM), microhardness (MH) and dynamic mechanical analysis (DMA). The samples exhibited a typical α-modification spherulite structure of isotactic polypropylenes crystallized from the melt. It was found that the most important factor affecting the structure and properties of these polymers is the isotacticity content. A clear molecular weight effect was also found for samples with low molecular weights. The microhardness and storage modulus values increased as crystallinity did. Accordingly, isotacticity degree is considered as the main parameter affecting the crystallinity of samples.

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“…This low DC at higher T c is considered to preserve the melt microphase structure even though the crystallization rate is low. Such a T c dependence of DC has been found and discussed for polyethylene random copolymers containing a small amount of comonomers such as vinyl acetate, 1-hexene, and 1-butene [28][29][30] . In these systems, it has been pointed out that the comonomers act as impurities for the crystallization of polyethylene and make the distribution of melting temperature broad.…”

Section: Structure Formation In Crystallization Of the Neat Copolymermentioning

confidence: 85%

Structure Formation and Crystallization Behavior of Ethylene-Isoprene Block Copolymers and Their Blends with Corresponding Homopolymers

et al. 2008

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Time-resolved simultaneous synchrotron small-angle X-ray scattering and differential scanning calorimetry experiments have been performed on crystallization of polyethylene-polyisoprene diblock copolymers (HEI or LEI) and their blends with corresponding homopolymers, polyethylene (PE) and polyisoprene (PIp). For the neat block copolymer having a 50 wt% of the crystalline component, preexisting microphase separation structure in the melt was kept at high and low crystallization temperatures T c (T c Ն94°C and T c Ͻ60°C), while disrupted at intermediate T c (60°CՅT c Ͻ94°C). This complex behavior was interpreted by combination of two mechanisms. The behavior in the crystallization below 94°C was attributed to the competition between the crystallization and chain diffusion rates, that is, the fast crystallization rate at lower T c makes it difficult to rearrange the phase structure in the melt. On the other hand, at a higher T c (Ն94°C), the preservation of the microphase separation structure was explained by a small degree of crystallinity due to the ethyl branch of polyethylene (hydrogenated poly(butadiene)). For HEI/PE blends, crystallization behavior was the simple superposition of those for HEI and PE, while, for HEI/PIp with a small composition of PE, suppression of crystallinity was observed. Crystallization kinetics in the neat block copolymer and all the blends was not so different from that in the PE homopolymer.Keywords Microphase separation, Structure formation, Crystallization, Polyethylene-polyisoprene block copolymer. Regular Articlee-Journal of Soft Materials, Vol. 4, pp. 12-22 (2008) amorphous component T g A 19,20) . When crystallization temperature T c is lower than T g A , that is, the amorphous component is in glassy state at T c , microphase separation structure in the melt is usually maintained in crystallization, because the microphase separation structure is frozen by the glassy domains 19,21,22) . On the other hand, when T c is higher than T g A , it has been reported that structural change in crystallization depends on the segregation strength between components (cN t ). Quiram et al. explored the crystallization of a high molecular weight polyethylene-poly(3-methyl-1-butene) block copolymer (strongly segregated system) with a polyethylene weight fraction f E of 0.27, and found that polyethylene crystallized within preexisting cylindrical microdomains 23,24) . Nojima et al. 25) also investigated a crystallization process of crystalline-rubbery amorphous block copolymers for poly(e-caprolactone)-polybutadiene (weakly segregated system) through a time-resolved smallangle X-ray scattering (SAXS) technique using synchrotron radiation as a light source, and observed that a preexisting SAXS peak from the microphase separation disappeared with development of a new peak originating from the long period of crystal lamellae. Furthermore, we have reported that a high molecular weight poly(ethylene glycol)-poly(butadiene) block copolymer (PEG-PBD), which is relatively strongly segrega...

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Isotacticity effect on crystallization and melting in polypropylene fractions: 1. Crystalline structures and thermodynamic property changes

Cited by 162 publications

References 48 publications

Critical roles of molecular dynamics in the superior mechanical properties of isotactic-poly(1-butene) elucidated by solid-state NMR

Critical roles of molecular dynamics in the superior mechanical properties of isotactic-poly(1-butene) elucidated by solid-state NMR

Molecular weight and tacticity effect on morphological and mechanical properties of Ziegler–Natta catalyzed isotactic polypropylenes

Structure Formation and Crystallization Behavior of Ethylene-Isoprene Block Copolymers and Their Blends with Corresponding Homopolymers

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