Synthesis of hypercrosslinked polymers with a spherical shell structure for highly effective cycloaddition of CO2 under ambient conditions

Abstract

CO₂ cycloaddition conversion is a promising strategy for converting CO₂ into high-value-added products. However, most of the research studies focused on CO₂ cycloaddition conversion under high temperature and/or pressure conditions. The cycloaddition of CO₂ and epoxides under ambient conditions remains a great challenge. Hypercrosslinked polymers (HCPs) bearing special sites that capture and convert CO₂ concurrently make them ideal catalysts for CO₂ cycloaddition conversion. Herein, we report a series of HCPs with well-defined spherical shell structures (HCPSSs) by using templates and controlling the monomer feeding rate. When fluoranthene and N,N′-bis(salicylidene)-ethylenediamine (Salen) were selected as monomers, after loading of Co²⁺, the CO₂ conversion yield of the resulting polymer (HCPSS-FLA-Salen-4-80-Co, HCPSS-FS-4-80-Co) was 94% with a turnover number (TON) of 2054 under ambient conditions, which is 52% higher than that of its bulk counterpart HCP-FS-Co (yield: 62%) and comparable to those of the reported materials. This high yield was attributed to that the hollow structure can reduce the mass transfer resistance and increase active site exposure. This work not only provides a general approach to improve the conversion rate of CO₂ cycloaddition, but also proposes a widespread and efficient strategy for the synthesis of HCPSSs by controlling the monomer feeding rate.