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

Abstract

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.

Structural evolution from poly(amic acid) to polyimide fibers during thermal imidization process

“…Apparently, the reduced intensities of the bands at 1530 cm −1 for C–N stretching of amide II and 1660 cm −1 for C=O stretching of amide strongly indicate that the amide group in PAA is consumed in the imidization process. As reported by Xu and Zhang, 18 CONH– and COOH– groups in PAA were strongly affected by the hydrogen bonding interaction between the PAA and the residual DMAc. Thus, the imidization and the decomplexation of the H-bonded DMAc occurred simultaneously when the PAA fiber was heated.…”

The retarding effects and structural evolution of a bio‐based high‐performance polyimide during thermal imidization

“…For clear analysis, the whole spectrum was split into two regions: 1300–1800 and 2400–3450 cm −1 . Some important imidization‐related peaks were confirmed and displayed in Table . With the progressing of thermal imidization, peaks of PAA will disappear: v (NH of amide segment, 3290 cm −1 ), (overtone and combination of OH, 2400–2600 cm −1 ), v (CO of amide segment, 1660 cm −1 ), δ (NH of amide segment, 1550 cm −1 ); peaks of imide ring will appear: v (CO of imide ring, 1777 cm −1 ), v (CO of imide ring, 1720 cm −1 ), v (CNC of imide ring, 1360 cm −1 ).…”

“…The 1% correlation intensity was regarded as noise and cutoff, and contour level was set as 15. The instructions for 2DCS were provided by some previous papers . The X‐ray diffractometer (Philips X'Pert Pro MPD DY129) was used for measuring morphology of thin films.…”

“…Recently, this technology was widely used to study on imidization process of PIs as well. For instance, thermal imidization mechanism of a solid‐state PAA film was investigated in details through 2DCS . The variation of carboxyl group during thermal imidization was observed by spectral changes derived from in situ FTIR and 2DCS .…”

Preparation of polyimide films via microwave-assisted thermal imidization

“…The absorption peaks at 1658, 1552 and 1316 cm À1 are assigned to the amide-I band, amide-II band and amide CN stretching vibration of PAA, respectively. [28][29][30] In addition, the absorption bands at 1228 and 1014 cm À1 are assigned to the C-O-C stretching vibration of the aryl ether in ODA moiety. With increasing temperature, the characteristic peaks of PI get stronger accompanied by a gradual decrease in the absorption peaks of PAA, implying the gradual conversion of CONH groups to the cycloimide rings.…”