Molecular Chain Flexibility and Dielectric Loss at High-Frequency: Impact of Ester Bond Arrangement in Poly(ester imide)s

• Published in: Chinese journal of polymer science Vol. 42; no. 8; pp. 1122 - 1133
• Main Authors: Li, Ya-Dong, Li, Hong, Feng, Lu-Kun, Bao, Feng, Wang, Ming-Liang, Zhu, Cai-Zhen, Zheng, Zhao-Hui, Ding, Xiao-Bin, Xu, Jian
• Format: Journal Article
• Language: English
• Published: Singapore Springer Nature Singapore 01.08.2024; Springer Nature B.V
• Subjects: Aromatic compounds; Characterization and Evaluation of Materials; Chemical bonds; Chemical synthesis; Chemistry; Chemistry and Materials Science; Condensed Matter Physics; Dielectric loss; Dielectric properties; Dissipation factor; Flexibility; High temperature; Industrial Chemistry/Chemical Engineering; Molecular chains; Molecular structure; Polyimide resins; Polymer Sciences; Research Article; Structural analysis; 5G communications; Molecular chain flexibility; Poly(ester imide)s; Dielectric properties; Humidity absorption
• ISSN: 0256-7679; 1439-6203
• DOI: 10.1007/s10118-024-3140-6

The evolution of high-frequency communication has accentuated the significance of controlling dielectric properties in polymer media. Traditionally, it has been theorized that rigid molecular chains lead to lower dielectric loss. However, the validity of this proposition at high frequencies remains uncertain. To scrutinize the correlation between chain flexibility and dielectric properties, we synthesized six poly(ester imide)s (PEIs) with systematically varied molecular chain flexibilities by modifying the ester’s substitution on the aromatic ring. The introduction of ester bonds bestowed all PEI films with a low dielectric dissipation factor ( D f ), ranging from 0.0021 to 0.0038 at 10 GHz in dry conditions. The dry D f displayed a pattern consistent with volume polarizability ( P/V ). Unexpectedly, PI-mmm-T, featuring the most flexible molecular chain, exhibited the lowest dielectric loss under both dry (0.0021 @ 10 GHz) and hygroscopic (0.0029 @ 10 GHz) conditions. Furthermore, the observed increase in D f after humidity absorption suggests that the high dielectric loss of PEI in applications may be attributed to its hygroscopic nature. Molecular simulations and characterization of the aggregation structure revealed that the smaller cavities within flexible molecular chains, after close stacking, impede the entry of water molecules. Despite sacrificing high-temperature resistance, the precursor exhibited enhanced solubility properties and could be processed into high-quality films. Our research unveils new insights into the relationship between flexibility and high-frequency dielectric loss, offering innovative perspectives on synthesizing aromatic polymers with exceptional dielectric properties.