.beta.-Hydrogen abstraction and regiospecific insertion in syndiotactic polymerization of styrene

Zambelli, Adolfo; Longo, Pasquale; Pellecchia, Claudio; Grassi, Alfonso

doi:10.1021/ma00174a063

Cited by 221 publications

(118 citation statements)

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“…The modifications with polymers could not only improve CNT dispersibility, but also the interfacial polymer-nanotube interaction within composite materials. Highly stereoregular polystyrene, such as sPS, has been synthesized to produce nearly 100% syndiotactic conformation with a specific metallocene catalyst [34], which has received considerable attention because of its high melting temperature, high crystallinity, rapid crystallization rate, low dielectric constant, good chemical resistance, and enhanced mechanical performance at elevated temperature [35][36][37][38]. In spite of these excellent properties, however, sPS has a disadvantage of its inherent brittleness.…”

mentioning

confidence: 99%

Non-isothermal crystallization kinetics of syndiotactic polystyrene polystyrene functionalized SWNTs nanocomposites

Xiong

Gao²,

Li³

2007

Express Polym. Lett.

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Carbon nanotubes (CNTs) are unique nanostructured materials with remarkable physical, mechanical and electronic properties [1][2][3][4]. These properties make them attractive for applications in many scientific and technological fields such as electronic structures [5], polymer composites [6], and biological systems [7]. Among these potential applications, the prospect of obtaining high-performance CNT based polymeric nanocomposites has attracted the efforts of researchers in both academia and industry [8]. The combination of organic polymer components with CNT fillers in a single material has extraordinary significance for the development of advanced materials with remarkable mechanical, electrical, thermal and multifunctional properties [9][10][11][12]. Moreover, polymer/CNT nanocomposites challenge traditional filled polymers (loadings of 20 wt% or more) in many of these areas by providing similar physical enhancements but with as little as about 1 wt% addition of dispersed nanotubes [13]. Previous CNT based polymeric nanocomposites reports include increased modulus, impact strength, heat distortion temperature, and barrier properties with decreased thermal expansivity [14][15][16]. In addition, these nanocomposites are finding potential applications such as electrostatically dissipative materials and aerospace materials [17]. Currently, several processing methods, including melt mixing, solution process and in-situ polymerization [18][19][20] Abstract. Non-isothermal crystallization kinetics were characterized by using differential scanning calorimetry (DSC) analysis on neat semicrystalline syndiotactic polystyrene (sPS) and its nanocomposites with polystyrene (PS) functionalized full-length single walled carbon nanotubes (SWNT-PS), which was prepared by copper (I) catalyzed click coupling of alkyne-decorated SWNTs with well-defined, azide-terminated PS. The crystallization behavior of neat sPS polymer was compared to its SWNT based nanocomposites. The results suggested that the non-isothermal crystallization behavior of sPS/SWNT-PS nanocomposites depended significantly on the SWNT-PS contents and cooling rate. The incorporation of SWNT-PS caused a change in the mechanism of nucleation and the crystal growth of sPS crystallites, this effect being more significant at lower SWNT-PS content. Combined Avrami and Ozawa analysis was found to be effective in describing the non-isothermal crystallization of the neat sPS and its nanocomposites. The activation energy of sPS determined from nonisothermal data decreased with the presence of small quantity of SWNT-PS in the nanocomposites and then increased with increasing SWNT-PS contents.

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confidence: 99%

Non-isothermal crystallization kinetics of syndiotactic polystyrene polystyrene functionalized SWNTs nanocomposites

Xiong

Gao²,

Li³

2007

Express Polym. Lett.

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“…Three different crystalline forms and clathrate structures have been described and studied essentially by Xray diffraction, 4 -13 electron diffraction, 14 -16 FTIR, 1 7 -20 solid state NMR, 23 • 24 and conformational energy analyses. 25 · 26 Following the nomenclature proposed in ref 9, the two crystalline forms a and /3 contain planar zig-zag chains (line repetition group tc and conformation (TTTT)") with an identity period c=5.IA, while the third one (the y form), as well as the clathrate structure (J-form) contain helical chains (line repetition group s(2/ I )2 and conformation (TTG -G -)z or (G + G +TT) 2 ) with identity period c = 1.sA.…”

mentioning

confidence: 99%

Crystal Structure of the α-Form of Syndiotactic Polystyrene

Rosa

Guerra

Petraccone

et al. 1991

Polym J

180

188

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ABSTRACT:Models for chain packing for ordered and disordered modifications of the a-form of syndiotactic polystyrene are suggested, through quantitative comparisons between X-ray diffraction intensities and calculated structure factors. According to the reported analysis, zig-zag planar chains are packed in the hexagonal unit cell proposed by Greis et al., but with different orientation and relative height of the phenyl groups. In particular, the phenyl groups 1n both ordered and disordered modifications are packed according to rhombohedral symmetry. The disorder in the a' modification corresponds to the statistical occurrence of two different, nearly isosteric, orientations of triplets of chains at well defined locations of a threedimensional lattice, which generate a rhombohedral symmetry for the whole unit cell.KEY WORDS Syndiotactic Polystyrene / a-Form / Crystal Structure / Order-Disorder Phenomena / The synthesis of highly stereoregular syndiotactic polystyrene (s-PS) has been reported recently. 1 -3 The polymer presents very complex polymorphic behaviour. Three different crystalline forms and clathrate structures have been described and studied essentially by Xray diffraction, 4 -13 electron diffraction, 14 -16 FTIR, 1 7 -20 solid state NMR, 23 • 24 and conformational energy analyses. 25 · 26 Following the nomenclature proposed in ref 9, the two crystalline forms a and /3 contain planar zig-zag chains (line repetition group tc and conformation (TTTT)") with an identity period c=5.IA, while the third one (the y form), as well as the clathrate structure (J-form) contain helical chains (line repetition group s(2/ I )2 and conformation (TTG -G -)z or (G + G +TT) 2 ) with identity period c = 1.sA.Conformational energy calculations, performed at our laboratories, 26 indicate that the conformations tc and s(2/1)2 have nearly the same energy.The general pattern is further complicated by the fact that both the a and f3 forms (characterized by the same tc chain conformation and different chain packing) can exist in different modifications having different degrees of structural order, so that two limiting disordered modifications (the a' and /J') and two limiting ordered modifications (a" and /J") have been described. 9In a recent paper 12 we proposed detailed models for the chain packing for the limiting (J' and /J" modifications, through quantitative comparisons between X-ray diffraction intensities and calculated structure factors; furthermore it was shown that the disorder present in the f3 form could correspond to a statistical occurrence of two different kinds of stacking of ordered bilayers of macromolecules.As far as the a form is concerned, a detailed description of the morphology of thin films by transmission electron microscopy has been given, 14 -16 Greis et al. 14 • 15 have proposed a hexagonal unit cell with a= 26.26A, in which clusters of three chains are packed according 1435

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“…23,24,[35][36][37] Figure 4 indicates a schematic representation of the δ-form complex model in which the two adjacent right-handed (-TTGG-) 2 , left-handed (-TTGG-) 2 helical sPS chains accommodated one symbolized guest molecule.…”

Section: Resultsmentioning

confidence: 99%

“…1,2 The clathrate is a crystalline form in sPS polymorphism and is called δ-form complex. In the δ-form complex, the organic molecule is placed in a molecular cavity formed by two adjacent sPS chains having the TTGG helical conformations.…”

mentioning

confidence: 99%

Study on δ-Form Complex in Syndiotactic Polystyrene-Organic Molecules System III. Fine Structures of Complexes with Xylene Isomers by Means of High-Resolution Solid-State 13C NMR Spectroscopy

Yamamoto

Kishi

Amutharani

et al. 2003

Polym J

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ABSTRACT:Syndiotactic polystyrene (sPS) is known to form a clathrate compound with p-xylene and m-xylene, called δ-form complex. In this study, the structures of the sPS/p-xylene and sPS/m-xylene systems were investigated by high-resolution solid-state 13 C nuclear magnetic resonance ( 13 C NMR) and X-ray diffraction. From the Miller indices of the (0,1,0) reflection, it was confirmed that the distance between sPS helical chains in the m-xylene system was longer than that of the p-xylene system. It was concluded that the location of one methyl group of m-xylene in the sPS δ-form complex coincided with that of one methyl group of p-xylene, because the 13 C NMR chemical shift and spin-lattice relaxation time of the methyl carbon of p-xylene were similar to those of one methyl carbon of m-xylene in the sPS δ-form complex. The meta substituted another methyl group of m-xylene showed a low-field chemical shift, indicating it close to the two phenyl groups of sPS chains in the δ-form complex.

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.beta.-Hydrogen abstraction and regiospecific insertion in syndiotactic polymerization of styrene

Cited by 221 publications

References 0 publications

Non-isothermal crystallization kinetics of syndiotactic polystyrene polystyrene functionalized SWNTs nanocomposites

Non-isothermal crystallization kinetics of syndiotactic polystyrene polystyrene functionalized SWNTs nanocomposites

Crystal Structure of the α-Form of Syndiotactic Polystyrene

Study on δ-Form Complex in Syndiotactic Polystyrene-Organic Molecules System III. Fine Structures of Complexes with Xylene Isomers by Means of High-Resolution Solid-State 13C NMR Spectroscopy

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