Formation of the α and γ Polymorphs in Random Metallocene−Propylene Copolymers. Effect of Concentration and Type of Comonomer

Hosier, I. L.; Alamo, Rufina G.; Esteso, P.; Isasi, José Ramón; Mandelkern, L.

doi:10.1021/ma030157m

Cited by 197 publications

(277 citation statements)

References 55 publications

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“…[32][33][34] Also, it has been found that the presence of ethylene monomer along the polypropylene chain disturbs the chain regularity and, consequently, decreases polymer crystallization ability; [34][35][36] e.g., its presence decreases crystallinity and linear growth rate and, moreover, induces the formation of the orthorhombic γ-phase. 36,37 However, the effects above have mostly been studied for quiescent crystallization, or under a rheometric flow 35 unable to impose high shear stresses similar to those typically encountered in industrial processing conditions. Here, we focus on the effect of the presence of defects in the molecular architecture on shear-induced crystallization.…”

Section: Introductionmentioning

confidence: 99%

High-Stress Shear-Induced Crystallization in Isotactic Polypropylene and Propylene/Ethylene Random Copolymers

Fernandez-Ballester

Cavallo

et al. 2013

Macromolecules

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IntroductionSemicrystalline polymers are usually processed from their molten state and subjected to intense shear and/or elongation flows. Such flow fields not only accelerate crystallization kinetics, which shortens the processing time, but can also change the morphology from isotropic spherulites to highly oriented shish-kebab structures 1-3 and, as a consequence, determine the ultimate product properties. Therefore, understanding the interplay between strong flow fields and the resulting structures is of importance for designing processing procedures to tailor these end product properties.Considerable work [4][5][6][7] has been devoted to this topic in the past half century. Many researchers have focused on the relation between shear flow and polymer crystallization, because shear fields are easily created with rotational 3 or sliding 8,9 plate-plate devices, on rotational rheometers, 10,11 and in pressure driven slit flows. 12,13 These test geometries are typically combined with time-resolved characterization techniques like mechanical spectrometry, 10, 11, 14 light scattering, 15,16 birefringence, 13, 17 X-ray scattering 7,18,19 and Fourier transform infrared (FTIR) spectroscopy, 9, 20, 21 etc. Significant progress has been made in understanding shear-induced crystallization, 4-7 while some of the fundamental issues remain unsolved. In particular, knowledge of basic mechanism of crystallization under high shear rates and stress-close to realistic processing conditions-is still limited. The need for such information is becoming urgent in order to improve the latest simulation models, since the results of numerical predictions of, for example, injection molding, 22 have to be validated and further refined from experimental evidence.Imposing a strong shear flow at chosen high shear rates or stresses under well-defined conditions requires a specially designed flow device. Both the pressure-driven slit flow apparatus constructed by Janeschitz-Kriegl et al. 12 and improved by Kornfield et al.,13 and the piston-driven slit rheometer developed by Mackley et al. 23 and modified by Peters and coworkers, 24,25 can operate in the high stress region (of the order of 0.1 MPa) and are easily combined with time-resolved birefringence 24,26 and/or X-ray scattering [27][28][29][30] AbstractCrystallization of an isotactic polypropylene (iPP) homopolymer and two propylene/ethylene random copolymers (RACO), induced by high-stress shear, was studied using in situ synchrotron wide-angle X-ray diffraction (WAXD) at 137 °C. The "depth sectioning" method (Fernandez-Ballester, Journal of Rheology 53:5 (2009), pp. 1229−1254) was applied in order to isolate the contributions of different layers in the stress gradient direction and to relate specific structural evolution to the corresponding local stress. This approach gives quantitative results in terms of the specific length of fibrillar nuclei as a function of the applied stress. As expected, crystallization becomes faster with increasing stress-from the inner to the outer layer-for...

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Section: Introductionmentioning

confidence: 99%

High-Stress Shear-Induced Crystallization in Isotactic Polypropylene and Propylene/Ethylene Random Copolymers

Fernandez-Ballester

Cavallo

et al. 2013

Macromolecules

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“…can crystallize into the c phase from melt, which is favored by high crystallization temperature or slow cooling rate due to kinetic limitation. [10][11][12] Unlike a form, the chain packing in the orthorhombic unit cell of c phase is nonparallel. Instead, the direction of the chain axis in adjacent bilayers is tilted by approximately 80 against each other and approximately 40…”

Section: Introductionmentioning

confidence: 99%

Effect of network relaxation on void propagation and failure in isotactic polypropylene at large strain

2009

J of Applied Polymer Sci

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The important role of network relaxation in the voiding and fracture toughness of isotactic polypropylene (iPP) has been explored with video-aid tensile tests, two-dimensional small-angle X-ray scattering (2D-SAXS) measurements, and morphological observations. The results indicated that macroscopic volume dilatation related to voiding became lower during large deformation of iPP sample with rich c phase (denoted as c-iPP) cooled at 1 C/min, compared with one with exclusive a form (referred to a-iPP) quenched in air. Furthermore, void propagation perpendicular to the tensile direction, demonstrated by Guinier approximation analysis of 2D-SAXS results, was suppressed to a large extent in such a c-iPP sample. Less network relaxation, resulted from its peculiar crystalline and amorphous phases, was responsible for lower volume dilatation and slower void propagation in the c-iPP sample. Meanwhile, less network relaxation and suppressed transverse void propagation contributed to higher toughness in the c-iPP sample.

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“…This conclusion is consistent with other authors that reported the similarity between isotactic polypropylene and polybutene conformations, which facilitates the inclusion of 1-butene in the iPP crystal structure. [35][36][37][38][39][40] Ethylene comonomer, due to its small size, is not excluded from the crystal lattice, but it interrupts the iPP helix, shortening the crystal sequence and incorporating these distorted sequences to the amorphous fraction of the polymer. [37,41,42] Figure 1a also shows the totally amorphous profile, amPP, of an elastomeric PP sample [30] , in this case scaled to account for the amorphous component corresponding to the terpolymer.…”

Section: Experimental Partmentioning

confidence: 99%

“…Polypropylene produced with a Ziegler Natta catalyst has a broad distribution of defects from chain to chain and a distribution of defects intramolecularly that deviates strongly from the random behavior: the defects are more concentrated in the molecules with lower molar mass [36]. Since the presence of short isotactic sequences is a requirement for the formation of the γ polymorph, it is not surprising that ZN iPP homopolymer leads to insignificant contents of crystallites of the γ form, contrary to the case of iPP synthesized with a metallocene catalyst with the same overall concentration of defects.…”

Section: 1 Samples With Q and S Treatmentmentioning

confidence: 99%

Influence of structure on the properties of polypropylene copolymers and terpolymers

et al. 2017

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A set of Ziegler-Natta copolymers of iPP with ethylene or with 1-butene, and terpolymers with both counits have been characterized, devoting special attention to the effect of composition and processing conditions on the crystal structure and on the final properties.DSC and X-ray diffraction is used to study the polymorphism of copolymers and terpolymers.Comonomer insertion interrupts the isotactic sequences, acting as a structural defect, and the formation of  form is enhanced in the interval of studied compositions. Moreover, crystallinity decreases and crystal structure is modified. Comonomer type and concentration determine the extent of these modifications, resulting on important changes in macroscopicproperties. An important aspect to be considered is the higher ability of 1-butene units to be incorporated in the iPP crystals in relation to ethylene counits. From the balance of different properties, possible applications are suggested for the various types of samples. For instance, the excellent optical properties of the analyzed terpolymers make them very attractive for applications such as transparent film or packaging.

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Formation of the α and γ Polymorphs in Random Metallocene−Propylene Copolymers. Effect of Concentration and Type of Comonomer

Cited by 197 publications

References 55 publications

High-Stress Shear-Induced Crystallization in Isotactic Polypropylene and Propylene/Ethylene Random Copolymers

High-Stress Shear-Induced Crystallization in Isotactic Polypropylene and Propylene/Ethylene Random Copolymers

Effect of network relaxation on void propagation and failure in isotactic polypropylene at large strain

Influence of structure on the properties of polypropylene copolymers and terpolymers

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