Density Fluctuations as Precursors of Crystallization in a Thermoplastic Polyimide

Ania, F.; Cagiao, M. E.; Calleja, F. J. Baltá

doi:10.1295/polymj.31.735

Cited by 5 publications

(2 citation statements)

References 14 publications

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“…In general, introduction of crystallinity in these materials can further substantially improve the thermal stability and enhance solvent resistance,4–6 as well as increase radiation resistance and partial retention of mechanical properties above the T g 7, 8. Therefore, semicrystalline polyimides have been the focus of considerable research over the recent years 9–29. Although many polyimides have been reported to exhibit crystallinity, most do not recrystallize, once taken to the melt.…”

Section: Introductionmentioning

confidence: 99%

Crystallization behavior of a thermoplastic polyimide derived from 3,3′,4,4′‐oxydiphthalic dianhydride and 4,4′‐oxydianiline

Zhao

Zhang

Men

et al. 2008

J of Applied Polymer Sci

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Nonisothermal and isothermal crystallization kinetics of an aromatic thermoplastic polyimide derived from 3,3 0 ,4,4 0 -oxydiphthalic dianhydride and 4,4 0 -oxydianiline have been investigated by means of differential scanning calorimetry (DSC) and wide-angle X-ray diffraction. The results for nonisothermal crystallization study showed that a weak melting peak appeared during the first heating process, whereas no crystallization peak appeared in the DSC curve during the subsequent cooling process. On the other hand, the study for the isothermal crystallization in the temperature range of 260-3308C showed that a new exothermic peak appeared at lower temperature for the samples crystallized for 100 min at 3008C. Moreover, the results indicated that the crystallization behaviors were largely affected by the crystallization temperature and crystallization time. During the annealing process, the melting enthalpy tended to increase with increasing annealing temperature and annealing time. More interesting was that two melting endotherms appeared when the annealing temperature was lower than 3008C. However, when the annealing temperature was higher than 3308C, only one melting endotherm appeared.

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Section: Introductionmentioning

confidence: 99%

Crystallization behavior of a thermoplastic polyimide derived from 3,3′,4,4′‐oxydiphthalic dianhydride and 4,4′‐oxydianiline

Zhao

Zhang

Men

et al. 2008

J of Applied Polymer Sci

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show abstract

“…[8 -10] SAXS studies on the glass crystallization of other semirigid polymers-PEEK, [11] PEN, [12] and PBT [13] -also supported the occurrence of electron density fluctuations as precursors of crystallization. Lately, the occurrence of electron density fluctuations broadened to include rigid glassy polymers (new TPI) [14] and melt crystallization of flexible polymers, like polypropylene. [15] However, in a more recent paper describing similar results for the melt crystallization of polyethylene, Hsiao and coworkers [6] pointed out that the sensitivity of SAXS was much higher (0.1% level) than that of WAXS (1% level), raising controversy to the suggestions of SAXS density fluctuations appearing before WAXD order.…”

Section: Introductionmentioning

confidence: 99%

Density Fluctuations as Precursors of Crystallization in Polyamide 6,6 Using Time-Resolved X-Ray Scattering Techniques

Ania

Flores

Calleja

2003

Journal of Macromolecular Science, Part B

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In the present study, attempts are made to throw light on the mechanisms leading to primary nucleation in polymer crystallization. Previous studies in this field are not conclusive. Aiming to investigate the induction period prior to crystallization, timeresolved simultaneous small-and wide-angle X-ray scattering (SAXS and WAXS) measurements have been made in situ for polyamide 6,6, while it was crystallized from the melt. For this polymer, it is confirmed that at a low supercooling ðDT < 288CÞ; during the induction period, a well-resolved SAXS pattern appears. The time evolution of this scattering pattern can be described by the kinetics of spinodal decomposition, as previously reported for the glass crystallization of PEKK and TPI. According to this analysis, a value for the most probable scattering vector q of density fluctuations at around 0.43 nm 21 is found. It corresponds to a characteristic wavelength of 14.7 nm of long-range density fluctuations growing with time.

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Transient and athermal effects in the crystallization of polymers. I. Isothermal crystallization

Sajkiewicz

2002

J Polym Sci B Polym Phys

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The isothermal crystallization of poly(propylene) and poly(ethylene terephthalate) was investigated with differential scanning calorimetry and optical microscopy. It was found that the induction time depends on the cooling rate to a constant temperature. The isothermal crystallization of the investigated polymers is a complex process and cannot be adequately described by the simple Avrami equation with time‐independent parameters. The results indicate that crystallization is composed of several nucleation mechanisms. The homogeneous nucleation occurring from thermal fluctuations is preceded by the nucleation on not completely melted crystalline residues that can become stable by an athermal mechanism as well as nucleation on heterogeneities. The nucleation rate depends on time, with the maximum shortly after the start of crystallization attributed to nucleation on crystalline residues (possible athermal nucleation) and on heterogeneities. However, the spherulitic growth rate and the exponent n do not change with the time of crystallization. The time dependence of the crystallization rate corresponds to the changes in the nucleation rate with time. The steady‐state crystallization rate in thermal nucleation is lower than the rate determined in a classical way from the half‐time of crystallization. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1835–1849, 2002

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Density Fluctuations as Precursors of Crystallization in a Thermoplastic Polyimide

Cited by 5 publications

References 14 publications

Crystallization behavior of a thermoplastic polyimide derived from 3,3′,4,4′‐oxydiphthalic dianhydride and 4,4′‐oxydianiline

Crystallization behavior of a thermoplastic polyimide derived from 3,3′,4,4′‐oxydiphthalic dianhydride and 4,4′‐oxydianiline

Density Fluctuations as Precursors of Crystallization in Polyamide 6,6 Using Time-Resolved X-Ray Scattering Techniques

Transient and athermal effects in the crystallization of polymers. I. Isothermal crystallization

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