Effect of hydrogen bonds on the solid phase cyclodehydration of polyamic acids

Shibayev, L.A.; Dauengauer, S. A.; Stepanov, N. G.; Chetkina, L. A.; Magomedova, N. S.; Bel'skii, V. K.; Sazanov, Yu. N.

doi:10.1016/0032-3950(87)90462-x

Cited by 9 publications

(3 citation statements)

References 5 publications

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“…The 2D-COS functions of φ(1550, 1525) > 0 and ψ(1550, 1525) > 0 indicate that the decrease of the band intensity at 1550 cm −1 occurs prior to that of 1525 cm −1 . According to the theory proposed by Denisov, 1,17,30,31 there exist two isomers for PAA: para and meta , and the para -segment is more likely to cyclize to form the imide ring than the meta -segment. Therefore, it is reasonable to presume that the IR band at 1525 cm −1 represents the meta -state PAA segment and the band at 1550 cm −1 represents the para-state, because the C-N-H bending of meta -segments is more restrained due to the steric hindrance and hydrogen bond, resulting in the lower vibration frequency than that of para -state PAA segment.…”

Section: Resultsmentioning

confidence: 99%

Two-Dimensional Fourier Transform Infrared (FT-IR) Correlation Spectroscopy Study of the Imidization Reaction from Polyamic Acid to Polyimide

Zhang

2014

Appl Spectrosc

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The mechanism of the thermal imidization of solid-state polyamic acid was studied using Fourier transform infrared (FT-IR) spectroscopy using the two-dimensional correlation spectroscopy method. It is assumed that two isomers exist in a polyamic acid segment: one is called the para-segment, which favors imidization reaction, the other is the meta-segment, which is not in favor for imidization unless the temperature is high enough. The results show that the imidization process differs for the two states of polyamic acid segments. The para-segment is more sensitive to the heat environment for the formation of imide ring, and it will take several intermediate steps to complete the ring closure at the aid of the solvent. As for the meta-segment, the ring will be closed before the imide formation due to the powerful energy provided in the high-temperature environment, and the ever-increasing chain rigidity and the loss of solvent during the heating process make this path the only option to continue the imidization process.

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Section: Resultsmentioning

confidence: 99%

Two-Dimensional Fourier Transform Infrared (FT-IR) Correlation Spectroscopy Study of the Imidization Reaction from Polyamic Acid to Polyimide

Zhang

2014

Appl Spectrosc

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“…It has been reported that the degree of in‐plane orientation is enhanced by an adequate amount of residual solvent 9. It is also known that PAA films prepared by casting from NMP contain considerable amounts of solvent through the hydrogen bonding of NMP with carboxylic groups in PAA 20–22. Therefore, poly(amide ester)s should contain less residual solvent, which could give polyimide films with lower in‐plane orientation, especially for the short alkyl esters.…”

Section: Resultsmentioning

confidence: 99%

Role of the in‐plane orientation of polyimide films in graphitization

Takeichi

Zuo

Hasegawa

2001

J Polym Sci B Polym Phys

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Poly(amide acid) labeled with perylenetetracarboxydiimide (PEDI) was prepared from 3,3Ј,4,4Ј-biphenyltetracarboxylic dianhydride (BPDA), p-phenylenediamine (PDA), and diamino-PEDI. Poly(amide acid) was then reacted with sodium hydride and various kinds of alkyl iodides for transformation into various poly(amide ester)s. The cast films were imidized while fixed on glass substrates to give BPDA/PDA polyimide films. The degree of in-plane molecular orientation (f) of the polyimides and their precursors, poly(amide acid) and poly(amide ester)s, were determined via measurements of the visible dichroic absorption at an incidence angle for a rodlike dye (PEDI) bound to the main chain. All precursor films showed relatively low degrees of in-plane orientation. After imidization of the precursors fixed on glasses, however, striking spontaneous in-plane orientation behavior was observed. The f value for polyimide film from a poly(amide acid) precursor was as high as 0.7-0.8. The f value for polyimide film from a methyl ester precursor, however, was lowered to 0.4 -0.5, but it increased with the increasing size of the alkyl groups. Good correlations of the in-plane orientation of the polyimide films with the tensile modulus of the films and the in-plane orientation of the graphitized films were observed.

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“…Important factors that affect the properties of PI films include the solvent–PAA interaction, the imidization degree, and the side reactions accompanying these processes, such as reversible anhydride formation 9. The solvent–PAA interaction has been well established by various authors 5, 6, 23, 24. They have revealed the existence of a hydrogen‐bonded complex between the solvent and PAA in addition to the free solvent molecules in PAA films.…”

Section: Resultsmentioning

confidence: 99%

Recovery of Acinetobacter radioresistens Lipase by Hydrophobic Adsorption to n‐Hexadecane Coated on Nonwoven Fabric

Wang

Chen

et al. 2003

Biotechnology Progress

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A simple and clean adsorption/desorption process was proposed for recovering Acinetobacter radioresistens lipase from fermentation broth. The adsorbent used was n-hexadecane coated on a hydrophobic nonwoven fabric (NWF). n-Hexadecane has a melting point of 16-18 degrees C, and its affinity for lipase decreases markedly from liquid to solid state. Accordingly, performing the adsorption and desorption above and below, respectively, the melting point would need no extraneous materials for separation. The adsorption isotherms at various temperatures were found to follow the Langmuir model. Simulation of the batch adsorption/desorption process showed that there exists an optimal amount of adsorbent for both concentration factor and enzyme recovery; the process is restrained by equilibrium. The performance of column adsorption/desorption could also be simulated using the adsorption isotherm, and it was shown that the concentration factor was proportional to the amount of adsorbent used. The benefits of this process include easy preparation of adsorbent, low operational cost, no extraneous materials needed, negligible enzyme denaturation, high efficiency, and simple process simulation.

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Effect of hydrogen bonds on the solid phase cyclodehydration of polyamic acids

Cited by 9 publications

References 5 publications

Two-Dimensional Fourier Transform Infrared (FT-IR) Correlation Spectroscopy Study of the Imidization Reaction from Polyamic Acid to Polyimide

Two-Dimensional Fourier Transform Infrared (FT-IR) Correlation Spectroscopy Study of the Imidization Reaction from Polyamic Acid to Polyimide

Role of the in‐plane orientation of polyimide films in graphitization

Recovery of Acinetobacter radioresistens Lipase by Hydrophobic Adsorption to n‐Hexadecane Coated on Nonwoven Fabric

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