The strong interchain packing and polarity of polyimide (PI) compromise its outstanding thermal and mechanical properties. Crown ethers are theoretically expected to form host–guest inclusion complex with PI and improve its disadvantages. On the basis of this hypothesis, we synthesized a series of PI/crown ether composite films and investigated their synthesis mechanism, structures and properties. Our results suggest that the introduction of crown ethers increased the free volume of PI matrix and generated a special necklace-like supramolecular structure, which simultaneously and greatly improved PI’s mechanical, dielectric and hydrophobic properties. The Young modulus, elongation and tensile energy at break of PI composite films were maximally increased by 73.0%, 135.5%, and 190.0%, respectively. Meanwhile their dielectric constant and water absorption were minimized by 16.6% and 66.8%, respectively. Crown ethers with different molecular sizes demonstrated different improvement effects on PI’s properties. Their inclusion rates stabilized at ∼50%, which are related to the equal reaction probability between anhydride and amino groups.

In this study, a maleimido-substituted aromatic s-triazine (TMT) was synthesized successfully via the nucleophilic substitution reaction between cyanuric chloride and N-(4-hydroxyphenyl) maleimide (HPM) formed from paraaminophenol and maleic anhydride; and its structure was characterized by flourier transform infrared spectroscope (FT-IR), 1H and 13C nuclear magnetic resonance (NMR), and elemental analysis (EA). The studied flame-retarded epoxy resins were obtained via thermal curing reactions among 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) modified epoxy prepolymer (DOPOER), 4,4′-diaminodiphenyl ethane (DDM) and TMT. Cure kinetics, flame-retardant, thermal and mechanical properties of the cured epoxy resins were characterized by differential scanning calorimeter (DSC), thermogravimeric analysis (TGA), limited oxygen index (LOI) measurement, UL 94 vertical burning test and mechanical test. The results indicate that TMT can promote the curing reaction of epoxy resins and decrease its apparent activation energy (Ea). Introduction of TMT can greatly improve flame-retardant, thermal and mechanical properties of the cured epoxy resins. Compared with the DOPOER/DDM system without TMT, LOI value of the cured epoxy resin can increase from 36.4% to 51.8%, and all samples can pass UL 94 V-0 rate when TMT content ranges from 1.98 wt% to 7.44 wt%. Its initial degradation temperature and glass transition temperature (Tg) can increase maximally by 37.6 °C and 12.6 °C, respectively when TMT content is 3.88 wt%.

High refractive index of epoxy resins used as encapsulant in light-emitting diode (LED) is essential in improving the light extraction efficiency, reducing heat and prolonging the service life of LED packages. In this study, diglycidyl ether of thiodibenzenethiol (DGETDBT), an epoxy resin with high refractive index, was synthesized via a novel method and its chemical structure was characterized with Fourier-transform infrared (FTIR) spectrometer and 1H NMR spectrometer. Using m-xylylenediamine (MXDA) as curing agent, the curing behavior of DGETDBT was studied by differential scanning calorimetry (DSC) and was compared with that of diglycidyl ether of bisphenol A (DGEBA), a generally used encapsulant in LED. The thermal behavior and optical performance of these two resins were investigated with thermogravimetric analyses, UV–Vis scanning spectrophotometer, and Abbe refractometer, respectively. The results showed that DGETDBT/MXDA resin demonstrated similar curing and thermal behavior to DGEBA/MXDA resin. But its refractive index reaches 1.698, which is significantly higher than that of DGEBA/MXDA resin (1.604). Comparatively, DGETDBT resin can be expected to be a more effective encapsulant of LED.