Thermally induced crystallization in glassy syndiotactic polystyrene

Candia, F. De; Filho, A. Ruvolo; Vittoria, Vittoria

doi:10.1007/bf00657401

Cited by 62 publications

(45 citation statements)

References 13 publications

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“…The results shown in Figures 6 and 7 are in agreement with previous studies 20,31,41 which showed that on annealing sPS in the range 120-220°C, the planar mesophase is nucleated first, which then converts into the poorly ordered R′ form. The extent of conversion depends on the annealing temperature and time.…”

Section: Resultssupporting

confidence: 91%

“…At 130°C, a temperature within the cold crystallization region of amorphous sPS, the diffraction pattern is that of the planar mesomorphic phase with T 4 conformation. 14,20,31 At 175 and 210°C, the pattern is essentially that of the mesophase with a hint of the evolution of the R phase. The R phase, however, is fully formed at 240°C; the crystals obtained under such conditions generally show broad reflections and have a low degree of perfection, and the crystalline phase is termed R′.…”

Section: Resultsmentioning

confidence: 97%

“…[16][17][18] Generally, the δ form contains solvent molecules entrapped in the crystal structure whereas the γ form is free of solvent. 7,19 The mesophase with the helical conformation is obtained by removing the solvent molecules from the δ-form, 13,14 and the mesophase with the zigzag conformation is obtained by annealing 20 or stretching 21 amorphous sPS above its T g .…”

Section: Introductionmentioning

confidence: 99%

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Effect of Compressed CO₂ on Phase Transitions and Polymorphism in Syndiotactic Polystyrene

1997

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When treated with compressed CO2, syndiotactic polystyrene (sPS) undergoes a number of solid-solid transitions that do not occur on treatment with liquid solvents. For example, planar mesophase f , R f , and γ f transitions can be brought about under appropriate conditions of temperature and CO2 pressure. In addition, the transitions of glassy sPS to the planar mesomorphic and to the R form, and the γ f R transition occur at temperatures lower than when the same transitions are effected under ambient pressure. The dissolved CO2 lowers the glass transition and the cold crystallization temperatures of sPS at the rate of -0.92 and -0.58°C/atm, respectively. Crystallization kinetics from the sPS-CO2 solution follow the Avrami equation, but the value of the exponent n is lower than when crystallization is conducted under ambient pressure.

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Section: Resultssupporting

confidence: 91%

Section: Resultsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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Effect of Compressed CO₂ on Phase Transitions and Polymorphism in Syndiotactic Polystyrene

1997

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“…Furthermore, a WAXD study near the melting region of about 270°C showed that the double endothermic melting behavior of sPS was caused not by a change in the crystalline form but by a recrystallization to a more perfect crystal [48]. The normalized crystallinity of sPS in the composites, X c , is given by the Equation (1): (1) where ΔH f is the melting enthalpy of sPS in the composites, ΔH f 0 is the melting enthalpy of 100% crystalline sPS (ΔH f 0 = 53 J/g) [49] and w is the weight fraction of sPS in the composites. A variation in the X c value depending on the nanotube contents was observed for the composites, i. e., for the sPS/SWNT-PS composites, the X c value increased drastically with the addition of a small amount of SWNT-PS (ca.…”

Section: Thermal Behaviormentioning

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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“…3 Additionally, two mesomorphic phases have been observed, with a helical conformation 20,21 and with a zigzag conformation. 22,23 Guerra et al 3 showed that its complex polymorphism depends on a combination of concurrent factors, such as the cooling rate, the parent's previous initial crystalline form before melting, the maximum temperature (T max ), and the residence time in the molten state.…”

Section: Introductionmentioning

confidence: 99%

Solidification of syndiotactic polystyrene by a continuous cooling transformation approach

Carrubba

Piccarolo

Brucato

2007

J Polym Sci B Polym Phys

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Syndiotactic polystyrene (sPS) was solidified from the melt under drastic conditions according to a continuous cooling transformation methodology developed by the authors, which covered a cooling rate range spanning from approximately 0.03 to 3000 8C/s. The samples produced, structurally homogeneous across both their thickness and surface, were analyzed by macroscopic methods, such as density, wide-angle X-ray diffraction (WAXD), and microhardness (MH) measurements. The density was strictly related to the phase content, as confirmed by WAXD deconvolution. The peculiar behavior encountered (the density first decreasing and then increasing with the cooling rate) was attributed to the singularity of the phases formed in sPS; that is, one of the crystalline phases (a) was less dense than the amorphous phase, and the latter, in turn, was less dense than the other crystalline phase (b). With an increasing cooling rate, the thermodynamically stable phase (b) disappeared first, and it was followed by the a phase. On the other hand, the MH values remarkably depended on the amount of the b phase, the a-phase content influencing the mechanical properties only to a minor extent. The behavior of the crystallization kinetics was described through a modified multiphase Kolmogoroff-Avrami-Evans model for nonisothermal crystallization.

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Thermally induced crystallization in glassy syndiotactic polystyrene

Cited by 62 publications

References 13 publications

Effect of Compressed CO₂ on Phase Transitions and Polymorphism in Syndiotactic Polystyrene

Effect of Compressed CO₂ on Phase Transitions and Polymorphism in Syndiotactic Polystyrene

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

Solidification of syndiotactic polystyrene by a continuous cooling transformation approach

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Thermally induced crystallization in glassy syndiotactic polystyrene

Cited by 62 publications

References 13 publications

Effect of Compressed CO2 on Phase Transitions and Polymorphism in Syndiotactic Polystyrene

Effect of Compressed CO2 on Phase Transitions and Polymorphism in Syndiotactic Polystyrene

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

Solidification of syndiotactic polystyrene by a continuous cooling transformation approach

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Product

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Effect of Compressed CO₂ on Phase Transitions and Polymorphism in Syndiotactic Polystyrene

Effect of Compressed CO₂ on Phase Transitions and Polymorphism in Syndiotactic Polystyrene