The In-plane Orientation and Thermal Mechanical Properties of the Chemically Imidized Polyimide Films

• Published in: Chinese journal of polymer science Vol. 37; no. 3; pp. 268 - 278
• Main Authors: Wang, Zhen-He, Chen, Xing, Yang, Hai-Xia, Zhao, Jiang, Yang, Shi-Yong
• Format: Journal Article
• Language: English
• Published: Beijing Chinese Chemical Society and Institute of Chemistry, CAS 01.03.2019; Springer Nature B.V
• Subjects: Anhydrides; Chain mobility; Chains (polymeric); Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Condensed Matter Physics; Evaporation; High temperature; Industrial Chemistry/Chemical Engineering; Mechanical properties; Molecular weight; Organic chemistry; Orientation; Polyimide resins; Polymer Sciences; Polymers; Thermal expansion; Thermodynamic properties; In-plane orientation; Polyimide film; Chemical imidization; CTE; Thermal imidization
• ISSN: 0256-7679; 1439-6203
• DOI: 10.1007/s10118-019-2173-8

The thermal and mechanical properties of the chemically imidized polyimide (CIPI) films and thermally imidized polyimide (TIPI) films were investigated systematically. Experimental results indicated that the CIPI films show dramatically enhanced tensile strength and modulus with obviously reduced coefficient of thermal expansion (CTE) in comparison with TIPI films. These enhancements results from the high in-plane orientation and close packing of the CIPI backbones. Compared with thermal imidization which starts at about 140 °C, the chemical imidization activated by acetic anhydride and isoquinoline initiates the cyclization even at room temperature. The resulting imide rings restrict the mobility of polymer chains and lead to the in-plane orientation with solvent evaporation. Additionally, fewer small molecules remain in the films after treated at 120 °C by chemical imidization than by thermal imidization. The polymer chain plasticization caused by the evaporation of small molecules at high temperature is obviously restricted. Moreover, the partially imidized polymer inhibits the decomposition of mainchains that occurs at subsequent high temperature process, being beneficial to the formation of high molecular weight PI films. Hence, chemical imidization pathway shows apparent advantage to produce PI films with great combined properties, including high modulus, strength and toughness, as well as high thermal dimension stability etc.