Modified Triphenylmethane-based Polyimides with Improved Optical, Dielectric and Solubility Properties via Post-Polymerization Modification

A family of new triphenylmethane (TPM)-based polyimides (PIs) containing bulky tert -butyldimethylsiloxy (TBS) side-groups (PI-TPMOSis) has been prepared by a post-polymerization modification via a simple silyl ether reaction of TPM-based PIs containing hydroxyl (OH) groups (PI-TPMOHs). The attachment of TBS side-groups in PI-TPMOSis can be achieved up to 100%, as confirmed by the 1 H-NMR and IR spectra. Due to the presence of the TPM structure, PI-TPMOSi films still display the excellent thermal stability with high glass transition temperature ( T g ) of 314–351 °C and high degradation temperature ( T d5% ) of 480–501 °C. It is quite remarkable that the introduction of TBS side-groups into PI-TPMOSi chains results in more superior optical, dielectric and solubility properties in comparison with the precursor PI-TPMOH films, probably due to the reductions of the packing density and charge-transfer complexes (CTCs) formation. The optical transmittance at 400 nm ( T 400 ) of PI-TPMOSi films is significantly increased from 45.3%–68.8% to 75.4%–81.6% of the precursor PI-TPMOH films. The dielectric constant ( D k ) and dissipation factor ( D f ) at 1 MHz of PI-TPMOSi films are reduced from 4.11–4.40 and 0.00159–0.00235 to 2.61–2.92 and 0.00125–0.00171 of the precursor PI-TPMOH films, respectively. Combining the molecular design and simple preparation method, this study provides an effective approach for enhancement of various properties of PI films for microelectronic and photoelectric engineering applications.