Phenanthrenequinone-Based Hyper-Cross-Linked Polymers via a Waste-Minimizing Friedel–Crafts Alkylation

Although hyper-cross-linked polymers (HCPs) offer significant advantages, their industrial scalability has been impeded by concerns regarding waste generation. To mitigate this challenge, we have successfully developed an efficient and cost-effective green synthesis method for phenanthrenequinone-based HCPs (PQ-HCPs). This method employs a Friedel–Crafts alkylation reaction, utilizing trifluoromethanesulfonic acid as a catalyst and PQ as the starting material. Under low catalyst concentrations, electrophilic sulfonation reactions are predominant. However, increasing the catalyst to a 2 equiv amount significantly shifts the reaction pathway toward Friedel–Crafts alkylation cross-linking. The resultant optimal sample, PQ-HCP-1:3, boasts an impressive specific surface area of up to 428 m2·g–1. Dye adsorption experiments on these samples demonstrated a marked selective affinity for Rhodamine B, with the hydrophilicity of the samples being a pivotal factor in the adsorption process. This innovative approach substantially outperforms traditional methods, which typically involve ferric chloride (FeCl3) and aluminum chloride (AlCl3), by significantly reducing the production of solid waste and effluent during the chemical reaction process.