Imparting low dielectric constant and high toughness to polyimide via physical blending with trifluoropropyl polyhedral oligomeric silsesquioxane

• Published in: Polymer engineering and science Vol. 62; no. 9; pp. 2809 - 2816
• Main Authors: Chen, Zhigeng, Zhang, Ying, Zhao, Jianqing, Mo, Yueqi, Liu, Shumei
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01-09-2022; Society of Plastics Engineers, Inc; Blackwell Publishing Ltd
• Subjects: Aggregates; composites; Composition; dielectric properties; Electric properties; Elongation; Mechanical properties; Miscibility; Permittivity; Phase separation; Polyhedral oligomeric silsesquioxane; Polyimides; Tensile tests; Thermal properties; Toughness; China
• ISSN: 0032-3888; 1548-2634
• DOI: 10.1002/pen.26063

Polyhedral oligomeric silsesquioxane (POSS) is commonly used to lower the dielectric constant of polyimide (PI), but the toughness generally deteriorates. In this paper, trifluoropropyl POSS (FPOSS) is surprisingly found to impart superior dielectric constant and toughness to PI, even though the phase separation and aggregation of FPOSS are observed due to the thermodynamical immiscibility between FPOSS and PI. The dielectric constant of FPOSS/PI with 2.0 wt% FPOSS is reduced to 2.47 from 3.17. Furthermore, the tensile energy to break of FPOSS/PI is unexpectedly increased to 10.2 MJ/m3 from 3.3 MJ/m3, indicating the great improvement in toughness. The toughening mechanism is ascribed to the debonding of FPOSS aggregates from PI matrix with a void growth during tensile test. Meanwhile, lateral coalescence of the voids is avoided due to the adequate inter‐aggregate distance when the width of the ligaments between the aggregates decreases with elongation of matrix.
By taking the advantage of the hydrogen bonding interaction between fluorinated POSS and the precursor of polyimide, the phase separation and aggregation of POSS in the polyimide matrix are effectively postponed despite the thermodynamical immiscibility between POSS and polyimide, resulting in the unexpected improvement in toughness of low‐dielectric‐constant POSS/polyimide composites.