The effects of atacticity, comonomer content, and configurational defects on the equilibrium melting temperature of monoclinic isotactic polypropylene

Bond, Eric Bryan; Spruiell, Joseph E.

doi:10.1002/app.1433

Cited by 16 publications

(13 citation statements)

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“…The conspicuous line narrowing observed in this spectrum reflects the rapid changes of conformations in the molten sample. Figure 1 shows that besides the lines observed at room temperature, the new resonance lines of CH 2 and CH carbons appear in the measured spectra with the rise of temperature. Similar effect was in the past observed in the spectra obtained using MAS DD 13 C NMR technique, i. e., without CP, on the PP crystallizing in $-form and these lines were assigned to the carbons within the chains of amorphous regions [7,11].…”

Section: Resultsmentioning

confidence: 99%

“…This process provides new types of metallocene PP (m-PP) different from previous Ziegler Natta PP types (ZN-PP), the main difference consisting in the production of grades with different stereoregularity (isotactic, syndiotactic, hemi-isotactic, atactic) [1] or narrow polydispersity of the polymer chains, compared to Ziegler-Natta catalysts, which produces only highly polydisperse isotactic polymers. The tacticity of isotactic (i) m-PP and ZN-PP is virtually the same (98% of isotactic diads), though the configurational defects are more frequent in m-iPP [2]; this might be reflected in a lower melting temperature of m-iPP in comparison with ZN-iPP. Comparing to ZN-iPP, m-iPP offers a unique balance of stiffness, transparency, and organoleptic properties which is not achievable with ZN-iPP.…”

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confidence: 97%

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High-resolution solid-state NMR study of isotactic polypropylenes

Fričová¹,

Uhrinova²,

Hronský³

et al. 2012

Express Polym. Lett.

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Since the commercialization of Ziegler-Natta process of polypropylene synthesis, this technology was for decades almost the only source of all grades of polypropylene (PP). Only at the end of the last century a new process was developed, based on metallocene catalysis. This process provides new types of metallocene PP (m-PP) different from previous Ziegler Natta PP types (ZN-PP), the main difference consisting in the production of grades with different stereoregularity (isotactic, syndiotactic, hemi-isotactic, atactic) [1] or narrow polydispersity of the polymer chains, compared to Ziegler-Natta catalysts, which produces only highly polydisperse isotactic polymers. The tacticity of isotactic (i) m-PP and ZN-PP is virtually the same (98% of isotactic diads), though the configurational defects are more frequent in m-iPP [2]; this might be reflected in a lower melting temperature of m-iPP in comparison with ZN-iPP. Comparing to ZN-iPP, m-iPP offers a unique balance of stiffness, transparency, and organoleptic properties which is not achievable with ZN-iPP. On the other hand, m-iPP is usually less rigid than ZNiPP homopolymers. Thus, any additional information on similarity or differences in m-iPP vs. ZNiPP behaviour seems to be of scientific as well as Abstract. The high-resolution solid-state 13 C NMR spectra were recorded for metallocene (m) and Ziegler-Natta (ZN) isotactic polypropylenes (iPP) in pelletized form using cross polarization (CP) and magic angle spinning (MAS) techniques within the temperature range of 20-160°C. Besides the CP MAS experiments also the MAS 13 C NMR spectra (without CP), MAS 1 H NMR spectra and rotating frame spin-lattice relaxation times T 1" ( 13 C) were measured at elevated temperatures. With the rise of temperature the splitting of CH 2 , CH and CH 3 signals into two components was detected in 13 C NMR spectra and assigned to amorphous and crystalline phases. The temperature dependences of chemical shifts and integral intensities obtained from the deconvoluted spectra provided information on the main chain and CH 3 groups motions in amorphous and crystalline regions of studied samples. While T 1" ( 13 C) values show that the rate of segmental motion in amorphous regions in m-iPP and ZN-iPP is virtually the same, larger linewidths in 13 Vol.6, No.3 (2012) 204-212 Available online at www.expresspolymlett.com DOI: 10.3144/expresspolymlett.2012.23 * Corresponding author, e-mail: olga.fricova@tuke.sk © BME-PT commercial importance. NMR investigation is considered to be one of the basic relevant methods. The high-resolution solid-state 13 C NMR studies of iPP reported NMR spectra recorded with combination of magic angle spinning (MAS), cross polarisation (CP) and dipolar decoupling (DD) techniques [3][4][5][6][7][8][9][10][11][12][13][14]. Since iPP can crystallize in several crystalline forms, depending on the crystallization temperature and on the presence of specific nucleating agents, the shape of the spectra was found to depend strongly on the physical treatment of the sa...

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 97%

High-resolution solid-state NMR study of isotactic polypropylenes

Fričová¹,

Uhrinova²,

Hronský³

et al. 2012

Express Polym. Lett.

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“…Indeed, thermal calorimetry shows increased T c with increasing xGnP loading for all samples (Table 1, Figure 4A) (Table 1, Figure 4B). However, the melting points of the IS-samples are less than those of the MC-samples, which is attributed to the tendency of metallocene iPP to have a higher concentration of regio-and stereo-defects, as well as a higher regio-to stereodefect ratio in the chain microstructure, compared to Ziegler-Natta iPP [25,[36][37][38][39]. These defects in chain microstructure ultimately decreases the iPP lamellar crystal thickness, and therefore T m .…”

Section: Morphology Of Ipp-xgnp Nanocompositesmentioning

confidence: 82%

In-situ polymerization of isotactic polypropylene-nanographite nanocomposites

Cromer

Scheel

Luinstra

et al. 2015

Polymer

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Isotactic Polypropylene-Exfoliated Graphene Nanoplatelet (iPP-xGnP TM ) nanocomposites were prepared through an in-situ polymerization technique and compared to analogous composites prepared by melt compounding. In-situ preparation of iPP-xGnP nanocomposites was accomplished via single site metallocene polymerization of propylene within a toluene dispersion of xGnP nanoparticles. The in-situ prepared nanocomposites were compared to analogous nanocomposites prepared by melt compounding of commercial Ziegler-Natta iPP with xGnP. Optical microscopy showed the in-situ prepared nanocomposites demonstrated poorer xGnP dispersion compared to composites prepared by melt compounding. All xGnP-reinforced nanocomposites demonstrated increased crystallization temperature, as well as increases in mechanical strength and modulus, relative to neat iPP. However, the non-linear mechanical properties were found to be influenced by the both the preparation method and nanoparticle loading. Nanocomposites prepared by in-situ polymerization generally demonstrated superior ductility and fracture toughness compared to composites prepared by melt compounding. The results are discussed with regard to the preparation technique and xGnP loading. IntroductionPolyolefin nanocomposites offer opportunities to improve the properties of polyolefins with relatively small amounts of reinforcement. Compared to traditional fiber-reinforced composites, nanocomposites only require small reinforcement concentrations (< 2 vol %) to create property improvements. Polyolefin nanocomposites have shown property improvements such as M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 3 mechanical reinforcement, controlled gas permeability, and increased electrical conductivity when compared to the neat polyolefin resins [1].Many researchers strive to improve the mechanical properties of polyolefins using nanoscale reinforcement in order to create new and economical materials. For example, interest in the automotive industry has been directed toward developing reinforced polyolefins to replace engineering thermoplastic and metallic automotive materials, enabling cost and weight savings [2]. Polyolefin nanocomposites are ideal materials for this application due to the availability of low cost nanoscale reinforcements and polyolefin resins.Recently, graphene nanoplatelets (GNPs) have been investigated as nanoreinforcements for polyolefins [3,4]. The production of GNPs can be achieved by the thermal exfoliation of mineral graphite. Most notably, Drzal et al. developed an efficient method to produce Exfoliated Graphene Nanoplatelets (xGnP TM ) using acid intercalation followed by microwave assisted exfoliation [5,6]. These nanoplatelets are ideal nanoscale reinforcements due to their high aspect ratio, surface area, stiffness, thermal conductivity, and nucleation efficiency for crystallization of polyolefins [3,4,7,8]. Typically, polyolefin-GNP nanocomposites demonstrate improved modulus, strength, and higher crystallization temperature, along with decreased st...

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“…In our previous work we examined the effect of isotacticity on T°m and found that polypropylenes with different isotacticities have similar equilibrium melting temperatures, 186°C, 28 and other authors reported the same findings. 43 This shows that isotacticity and comonomer content have different effects on T°m. Isotacticity does not affect T°m, although comonomer reduces T°m.…”

Section: Melting Behaviormentioning

confidence: 95%

Isothermal crystallization of metallocene‐based propylene/α‐olefin copolymers

Zhang

Guan

et al. 2005

J of Applied Polymer Sci

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Isothermal crystallization and subsequent melting behavior of two propylene/hexene-1 copolymers and two propylene/octene-1 copolymers prepared with metallocene catalyst were investigated. It is found that ␥-modification is predominant in all copolymers. The Avrami exponent shows a weak dependency on comonomer content and comonomer type. At higher crystallization temperatures (T c ) the crystallization rate constant changes more rapidly with T c and the crystallization half-time substantially increases. Double melting peaks were also observed at high T c , which is attributed to the inhomogeneous distribution of comonomer units along the polymer chains and the existence of crystals with different lamellar thicknesses. The equilibrium melting temperatures (T°m) of the copolymers were obtained by Hoffman-Weeks extrapolation. It was found that the T°m decreases with increasing comonomer content, but are independent of comonomer type, implying that comonomer units are excluded from the crystal lattice. Dilation of the crystal lattice was also observed, which depends on crystallization, comonomer content, and comonomer type.

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The effects of atacticity, comonomer content, and configurational defects on the equilibrium melting temperature of monoclinic isotactic polypropylene

Cited by 16 publications

References 53 publications

High-resolution solid-state NMR study of isotactic polypropylenes

High-resolution solid-state NMR study of isotactic polypropylenes

In-situ polymerization of isotactic polypropylene-nanographite nanocomposites

Isothermal crystallization of metallocene‐based propylene/α‐olefin copolymers

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