Rapid, Mild Synthesis of Transparent Polyimides with High Refractive Index via Thiol-Michael Click Reaction

Polyimides (PIs) are widely used in microelectronics and advanced optical industries due to their excellent overall properties. However, the efficient and mild synthesis of PIs from commercially available raw materials poses great challenges in polymer chemistry. Here, a rapid and versatile thiol-Michael click reaction between imide-containing bismaleimides (BMI) and aromatic dithiol is developed. The structural diversity of the imide-containing BMI allows for manipulation of the optical and thermal properties by a molecular design with different substituents or dianhydrides in the backbone. The polymerization is good enough so that it can be completed in only 1 min at room temperature (25 degrees C) in the presence of triethylamine, affording high molecular weight PIs with good thermal stability, high tensile strength of up to 126.7 MPa, and desirable solubility and processability. With the structural design of the PIs and the introduced sulfur elements, the refractive indices of PIs are as high as 1.6601, while ensuring a high optical transmittance of up to 85% at 400 nm. This thiol-maleimide click polymerization significantly speeds up the preparation of functional PIs that have potential applications in advanced optical devices.