Spectroscopic Manifestations of Nitrile Group Intermolecular Attraction in PAN

Andreeva, O. A.; Burkova, L. A.

doi:10.1081/mb-100100381

Cited by 10 publications

(12 citation statements)

References 12 publications

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“…1a, curve 1) and those of acrylic acid: 1720, 1780 cm −1 ν(C= =O) and 3200, 3500 cm −1 ν(OH) for the dimer and monomer, respectively. It has been shown previously that the first temperature corresponds to the first glass transition of PAN (14) and the second one indicates the onset of cyclization (15). 1a Figure 2 presents the temperature dependence of optical density of the nitrile band (2240 cm −1 ) for PAN (curve 1), CP 1 with a small amount of water (curve 2), CP 1 with a large amount of water (curve 3), and CP 2 with a large amount of water (curve 4).…”

Section: Resultsmentioning

confidence: 90%

Study of Two-Phase Behavior of Nitrile Polymers by in Situ Hot-Stage Ir Spectroscopy

Andreeva

Burkova

2001

Journal of Macromolecular Science, Part B

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The temperature behavior of polyacrylonitrile with a small number of acidic groups incorporated in its chains was studied by in situ hot-stage IR spectroscopy. It has been shown that acidic groups trigger the hydrolysis of nitrile groups at temperatures below the first glass point of polyacrylonitrile. At higher temperatures, the acidic groups separate from the hydrophobic polymer and aggregate to form clusters. This leads to the appearance of a second phase characterized by its own higher temperature glass transition at 140 • C. It is also shown that acidic groups do not trigger the cyclization reaction, and that their availability reduces of the reaction rate.

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Section: Resultsmentioning

confidence: 90%

Study of Two-Phase Behavior of Nitrile Polymers by in Situ Hot-Stage Ir Spectroscopy

Andreeva

Burkova

2001

Journal of Macromolecular Science, Part B

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“…6,17,18 Blue and red shifts of the nitrile stretching absorption band are possible for both acetonitrile and PAN. The direction of the shift is diagnostic of the interaction of nitrile with surrounding molecules.…”

Section: Resultsmentioning

confidence: 99%

“…The annealing temperature to rearrange the PAN chains at 120°C is far lower than the dissociation of CN interactions observed in the PAN bulk at 150-180°C. 10,17 The differences in the annealing temperatures between the bulk and the sapphire interface could be 2271 2268 2264 2262 2261 2261 2261 compound 2, CH 3 CHCNCH 3 2253 2250 2245 2243 2242 2241 2241 compound 3, CH 3 CH 2 CHCNCH 2 CH 3 2250 2246 2242 2240 2239 due to the enthalpic forces driving the interactions between the hydroxyl and the CN groups. 3.3.…”

Section: Resultsmentioning

confidence: 99%

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Molecular Origin of Solvent Resistance of Polyacrylonitrile

et al. 2009

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We report on the first in-situ sum frequency generation (SFG) spectroscopy characterization of polyacrylonitrile (PAN) interfacial interactions with air, sapphire, water, and heptane. Using the shift in the resonance frequency of CN at various interfaces, we demonstrated that PAN interacts with the surface hydroxyl of sapphire substrate through the lone pair orbital of nitrogen in the "end-on" configuration (σ-H bond). We also demonstrated that the CN-CN interaction is the main reason for the superior chemical resistance property of PAN. At room temperature the interaction between the polymer chains is much stronger than the interaction between the polymer and solvent molecules including water and heptane. At high temperatures, however, the interaction between the nitrile groups of the polymer weakens, making interaction possible between the nitrile groups and the surface hydroxyls of the substrate and water. These results provide an important insight as to why acrylonitrile when copolymerized with butadiene to form nitrile rubber results in one of the best known synthetic oil-resistant rubber.

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“…The first elongation temperature (FET) occurs because of the decay of intermolecular pairs of antiparallel nitrile dipoles in a fairly wide temperature. 40 FET for P1, P2, and P3 under 0.5 cN/tex stresses is 56, 58, and 62°C, respectively. With an increase of imposed stress, FET for every sample is decreased because of stress-temperature superposition.…”

Section: First Return Behaviormentioning

confidence: 99%

A Novel Method for Investigation of Entropic Stress in Prestabilization of PAN‐Based Precursor Fibers

2015

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ABSTRACT:Applying stress in the fiber axis direction during the prestabilization process is the best method to control entropic relaxation. Evaluation of entropic stress is necessary for exact determination of required imposed stress. Accordingly, in this paper three types of special-grade polyacrylonitrile (PAN) fibers with different physical-mechanical properties and morphological characteristic are studied. To determine thermal-induced entropic stresses, we use the thermomechanical analysis method from room temperature to beginning of chemical reactions under certain stresses. It is shown that three thermophysical behaviors including the first return, second return, and sans return occurs under certain stresses during the thermal process. There are distinct temperatures for the first and second return behaviors, in which fibers return to primary length after shrinkage or elongation. These temperatures depend on imposed stress during prestabilization. We found that if no elongation or fiber shrinkage occurs in a specific stress and temperature, it shows that imposed stress is equivalent to thermal entropic stress. Changes in shrinkage as a function of temperature for various external imposed stresses are also observed. According to our findings, the onset of entropic stress strongly depends on the orientation index of the paracrystalline region. The maximum entropic stress occurs in the rubbery flow region in amorphous phases and can be obtained from a derivative of the second-order polynomial trend line of the entropic stress-temperature diagram.

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Spectroscopic Manifestations of Nitrile Group Intermolecular Attraction in PAN

Cited by 10 publications

References 12 publications

Study of Two-Phase Behavior of Nitrile Polymers by in Situ Hot-Stage Ir Spectroscopy

Study of Two-Phase Behavior of Nitrile Polymers by in Situ Hot-Stage Ir Spectroscopy

Molecular Origin of Solvent Resistance of Polyacrylonitrile

A Novel Method for Investigation of Entropic Stress in Prestabilization of PAN‐Based Precursor Fibers

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