Decomposition pathway of polyimide

Polyimide can be decomposed in three ways: thermal oxidation decomposition, hydrolysis and radiation decomposition.

(1) Thermal oxidative decomposition. The research object of thermal decomposition is mostly Kapton (PMDA/ODA). In 1964, Bruck found that under 1.3 x 10.4Pa, at 620 ℃, 700 ℃ 800 ℃ and 850 ' (2) pyrolysis was carried out, and the density of the film increased to 1.659/cm3 at 800 ℃, and then a plateau appeared with the increase of temperature. The film remained intact and had a certain strength. This was because the aromatic ring was fused at high temperature and graphitized. Gay et al. Also studied the pyrolysis behavior of Kapton under 0.13pa vacuum, and thought that the imide ring was decomposed first at 400 ~ 600 ℃, and the products were mainly CO and C02. Fedotova et al. Also confirmed the decomposition of polyimide.

(2) Hydrolysis. The structure of polyimide determines its hydrolysis stability. The greater the electronic affinity of the carbonyl group of the dianhydride synthesized from polyimide, the lower the hydrolysis stability of the polyimide obtained from it. Among different polyimide varieties, Kapton is the easiest to hydrolyze, while upilex, ULTEM and yhpi are relatively difficult to hydrolyze. In the hydrolysis process, the polyimide is attacked by - OH, ring opening becomes polyamide acid or its salt, and then the amide bond is hydrolyzed to form amine, diacid or its salt. If the temperature is higher, the ether bond is hydrolyzed to form diphenol.

(3) Radiation decomposition. All aromatic polyimides have high radiation stability in general. However, in the 1990s, Hoyle's experiment found that for the polyimide film containing fluorine After irradiation at 9cm of Hanovia medium pressure mercury lamp, the absorption of IR spectrum becomes weak, while the UV spectrum is blue shifted, and the sample weight decreases with irradiation time. At the same time, GPC studies found that the molecular weight of fluoropolymer decreases after irradiation.