Molecular design of some semi-alicyclic polyimides as a route to improve refraction and dielectric properties for liquid crystal display applications

The study establishes an adequate monomer combination for achieving the best balance of properties required in obtaining polyimide alignment layers for display devices. The molecular design of some aliphatic/aromatic polyimides was performed by using dianhydride monomers with distinct configurations in terms of rigidity, size, and symmetry. The polyimides based on semi-flexible and nonsymmetric dianhydride moieties present lower refractive index and dielectric constant (<3) than those obtained from symmetric and rigid dianhydride units. This determines faster traveling of visible and microwave radiations as required for liquid crystal alignment purposes. The interactions of samples with the N-(4-Methoxybenzylidene)-4-butylaniline, cyanobiphenyl, and 4-pentyl-4-cyanobiphenyl nematics were assessed. The analyzed polyimides have higher surface tensions than the ones of the liquid crystals, determining a parallel arrangement of the nematic molecules. As the dispersive interactions at the polymer surface are lower, the work of spreading is higher as a result of improved adhesion of liquid crystal with the polyimide alignment layer. The sample containing rigid, symmetric, noncoplanar dianhydride units (PI.4) and the one based on semi-flexible, nonsymmetric dianhydride moieties are the most transparent for visible and microwave radiations, allowing low cohesion interaction at interface with nematics. These aspects recommend the two studied polyimides as candidates for alignment layers.

Synthesis and properties of highly soluble branched polyimide based on 2,4,6-triaminopyrimidine

A series of novel soluble polyimides was synthesized from commercially available 2,4,6-triaminopyrimidine (TAP), 2,2-bis(3,4-dicarboxylphenyl) hexafluoropropane dianhydride (6FDA), α,ω-aminopropylpoly(dimethylsiloxane) and 1,3-bis(3-aminophenoxy)benzene. TAP is the branched monomer, and polymerization process had been improved in three ways by using TAP to prepare soluble polyimides. The polyimides were characterized by Fourier transform infrared spectra, proton nuclear magnetic resonance, ultraviolet–visible spectrometer analysis, wide-angle X-ray diffraction, and size-exclusion chromatography with multiangle laser light-scattering detection. The branched polyimides showed excellent solubility both in strong polar solvents and in common low-boiling point solvents. Differential scanning calorimetric and thermogravimetric analyses showed high glass transition temperatures and excellent thermal stability for branched polyimides with moderate content of TAP. Polyimide membranes were formed at relatively low temperature, and the mechanical properties were tested. These results ensure that soluble polyimides with moderate content of TAP showed outstanding combined features and are desirable candidate materials for advanced applications.

Synthesis and characterization of optically active polyimides and their octa(aminophenyl)silsesquioxane nanocomposites

New optically active diamine (3,5-diaminophenyl)((R)-3,4-dihydro-1-phenylisoquinoline-2(1H)-yl)methanone was successfully prepared. Optically active polyimides (PIs) were synthesized by reacting the prepared diamine with the aromatic tetracarboxylic dianhydrides, namely, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride/pyromelltic dianhydride by thermal imidization method and characterized using Fourier transform infrared and nuclear magnetic resonance spectral techniques. Additionally, PI nanocomposites were also prepared by incorporating amino-functionalized polyhedral oligomeric silsesquioxane named as octa(aminophenyl)silsesquioxane (OAPS). The cut-off wavelengths of PIs and their nanocomposites were found to be less than 350 nm, indicating that the PIs are transparent. The PIs and their nanocomposites were found to have glass transition temperature between 204°C and 269°C (differential scanning calorimetric analysis). The 10% weight loss temperature and char yield were found to be 319.5–420.3°C and 26.3–62.7%, respectively. The PIs were found to be amorphous as indicated by X-ray analysis. The scanning electron microscopic images of the nanocomposites also reveal uniform distribution of the nanoparticles in the nanocomposite. PIs and PI/OAPS nanocomposites were found to have low dielectric constant in the range of 2.59–3.36.