WAXS in-situ study of R-BAPB polyetherimid double-melting behavior. (April 2022)

• Record Type: Journal Article
• Authors: Ivan'kova, E.M.; Kasatkin, I.A.; Popova, E.N.; Didenko, A.L.; Yudin, V.E.
• Is Part Of: Polymer testing. Volume 108(2022)
• Publication Date: 2022-04
• Subjects: Polyetherimid -- Reactor powder -- WAXS -- SEM -- DSC; Polymers -- Testing -- Periodicals; Polymères -- Tests -- Périodiques; 620.1920287
• DOI: 10.1016/j.polymertesting.2022.107522
• Languages: English
• ISSNs: 0142-9418

Abstract

Abstract: Reactor particles of nascent polyetherimid (PI) R-BAPB powder consist of numerous morphological units of the lamellar type, which have semicrystalline structure. Two endo-peaks at 318 °C and 340 °C were observed in the DSC thermogram of the PI powder. A unique in-situ thermo-WAXS experiment showed no significant difference in X-ray peak profiles when the sample was heated from room temperature up to 330 °C, (the valley between the low- and high-temperature endo-peaks). At that point the WAXS reflections became sharper and much better resolved without a visible crystal cell transformation. It was revealed that the degree of crystallinity dropped near 330 °C and continued decreasing until the complete melting of the sample. The low-temperature endo-peak is associated with melting of numerous small crystallites leading to the sharp amorphization of the sample and to a significant increase in the apparent crystallite size at 330 °C. The high-temperature endo-peak can then be attributed to melting of the larger crystallites formed from the melt during isothermal crystallization at 330 °C. Using WAXS profiles, it was also possible to evaluate the volumetric coefficient of thermal expansion of the crystalline part of the studied polymer as CTEvol = 3.8·10 −4 K −1 . Highlights: The polyetherimid R-BAPB reactor powder consisting of lamellar morphological units shows double melting behavior when heated. In-situ thermo-WAXS test reveals possible changes in the crystalline structure of the R-BAPB powder at elevated temperatures. No crystal cell transformation has been found on heating up to the sample melting. The volumetric coefficient of thermal expansion of the polymer crystalline part is estimated.