Significant Influence of Alkyl Substituents in the Alicyclic Rigid Backbone on Solubility and Thermal Stability of Polyarylamide Copolymers

Incorporation of alicyclic structural units in a polymer backbone holds great promises for preparing polyarylamides with superior physical properties (solubility, optical transparency, thermal stability, etc.). In this study, the alicyclic-containing building block, tetraethyl-substituted dibenzocyclooctadiene (TE-DBCOD), was integrated into the backbone of polyarylamides through a unique diamine monomer, TE-DBCOD-NH₂. The TE-DBCOD-containing polyarylamides were synthesized first through polycondensation with different contents of TE-DBCOD units. Compared to the control polymers without DBCOD or ethyl side-chain units, the polyarylamides with TE-DBCOD units showed better solubility in less polar solvents (m-cresol, pyridine, and tetrahydrofuran) and higher glass transition temperature (T_g), which provides an opportunity to fabricate polyarylamides with both improved solubility and T_g. Meanwhile, we also prepared the poly­(amide-imide)­s with TE-DBCOD by a two-step method for comparison. In contrast, the aromatic poly­(amide-imide)­s showed better solubility and lower T_gs than the corresponding aromatic poly­(amide-imide)­s without TE-DBCOD contents, which revealed the complex influence of structure parameters on different polymers. Additionally, the synthesized polymers possessed high thermal stability (5% weight loss temperature > 440 °C) verified by thermogravimetric analysis. The strategy of introducing short side chains in polymer backbones opens a window for exploration of polymers with improved solubility and increased T_g simultaneously, which also facilitates the understanding of the structure–property relationship of polymers with alicyclic structural units.