Cooperative synergistic effects of multiple functional groups in amide-containing polyimides with pyridine ring and pendent tert-butyl

In this work, pyridine ring and pendent tert-butyl were introduced into the diamine NTPA in view of improving the processability and transparency of the PIs via inhibiting charge-transfer complexes (CTCs). Meanwhile, the amide linkage was simultaneously introduced in order to boost the thermal and mechanical properties of the PIs by reasonably increasing the polymer stiffness via noncovalent amide H-bonding. The dianhydride BPADA was employed in the copolymerization with the diamine comonomers of NTPA with ODA in different ratios. Due to the presence of tert-butyl and pyridine ring, the synthesized co-PIs showed good optical properties with T₅₀₀ higher than 75% for all co-PIs, reaching 83% for homopolymer BPADA-NTPA, higher solubility in organic solvents, and better hydrophobicity with maximum hydrostatic contact angle as high as 91.9°. Meanwhile, the amide H-bonding increased the mechanical properties of co-PIs with the maximum tensile strength reaching 127 MPa. Furthermore, amide H-bonding exceedingly offset the reducing effects of pendent bulky butyl groups on the thermal properties of PIs, and the T_g of the co-PIs containing NTPA moiety ranged in 244–298°C, remarkably higher than 218°C for homopolymer BPADA-ODA. This work proved cooperative synergistic effects of multiple functional groups in balancing the general properties of co-PIs.