Controllable Oligomerization of Isobutene Catalyzed by Functional Poly(Ionic Liquid)s with Dispersed Acid Sites

Oligomerization of C4 olefins is one of the important pathways to utilize this type of resource for the production of high value-added chemicals. The spatial distribution of acid sites in the catalyst is closely related to the catalytic performance and product distribution. Ionic liquids (ILs) are a promising class of catalysts for butene oligomerization. Fabricating an ionic liquid into a poly(ionic liquid) is an effective approach to regulate the acid site distribution. Herein, various acidic poly(ionic liquid)s were synthesized by changing the polymerization method, copolymer block monomer structure, porogens, and assembly sequence during the synthesis process. Characterization results indicated that polymerizing the acidic ionic liquid monomer (1-vinyl-3-sulfobutylimidazolium triflate) with an appropriate amount of cross-linker (divinylbenzene) could effectively regulate the spatial distribution of active sites. The addition of lipophilic comonomers improved the lipophilicity of poly(ionic liquid)s to enhance the miscibility between butene and the catalyst. Moreover, it was found that adjusting the assembly sequence can further disperse the spatial distribution of the active sites of the IL monomer. The poly(ionic liquid) obtained by assembling the comonomer first and then copolymerizing the IL monomer and divinylbenzene, i.e., APIL-DVB@PDVB-EGDMA, contained a sufficient amount of Brønsted acid and exhibited good lipophilicity, with further improved spatial dispersion of acidic sites. When APIL-DVB@PDVB-EGDMA was used as the catalyst, isobutene was completely converted within 1 h, and the dimer selectivity reached 72.4%, in comparison with 100% for conversion and 39.2% for dimer selectivity in the catalysis by the ionic liquid monomer after 3 h.