Thermal, Optical, and Dielectric Properties of Bio-based Polyimides Derived from an Isosorbide-containing Dianhydride and Diamines with Long Alkyl Chains

A series of novel semi-aliphatic polyimides (PIs) were synthesized from a dianhydride containing bio-derived isosorbide (ISSDA) moiety and three types of aliphatic diamines with long alkyl chains including a bio-based dimer diamine (DDA). The bio-based content (C-B) of the ISSDA-DDA PI is as high as 65 wt%. The PIs derived from ISSDA and aliphatic diamines (ISS-APIs) exhibit excellent optical properties, such as very low refractive indices (n(av) < 1.566) and birefringence (Delta n < 0.00124). These are attributable to the flexible alkyl chains in the PIs which reduce the intermolecular interactions and the orientation of main chains. Furthermore, the low polarity of alkyl chains and the low content of polar groups in the PIs also decrease the electronic polarizability and local oscillating motions, resulting in excellent dielectric properties, such as very low dielectric constants (D-k < 2.938) and dissipation factors (D-f < 0.00964) at high frequencies (10 and 20 GHz). Despite their low glass transition temperatures of 47-152 degrees C, the 5 wt% weight-loss temperatures of ISS-APIs are as high as 400 degrees C. This study demonstrates the characteristic properties of the semialiphatic PIs which exhibit excellent optical, dielectric, and thermal properties while maintaining high C-B.