Synthesis of low molecular weight polyisobutylene using a sulfonated polyionic liquid as co-initiator

This study investigates the polymerization of Raffinate-1 to produce conventional-grade polyisobutylene (PIB) using aluminum chloride (AlCl₃) in combination with a sulfonated polyionic liquid (SO₃-PVI) as a co-initiator. The inclusion of SO₃-PVI enhances the stabilization of carbocationic intermediates, enabling reduced AlCl₃ loading by 33% while increasing the molecular weight of the resulting polymers. Structural confirmation of the sulfonated polyionic liquid was achieved via FTIR, while polymer characterization was done through GPC, NMR, and simulated distillation techniques. GPC analysis revealed a shift in molecular weight distribution toward higher values with the co-initiator system, indicating improved control over chain growth. NMR studies showed increased isobutylene content and end-group reactivity, contributing to desirable polymer properties. Simulated distillation confirmed the higher boiling point range of PIBs produced with SO₃-PVI. Density Functional Theory (DFT) simulations, supported by Mayer Bond Order, steric maps, Natural Bond Orbital, and Non-Covalent Interaction analyses, revealed favourable interactions between AlCl₃ and sulfonate groups, which stabilize the initiator system without overly sequestering AlCl₃. These findings suggest that incorporating sulfonated polyionic liquids in cationic polymerization offers both mechanistic and practical advantages for PIB production. More active sites are possible due to sulfonated IL, which is advantageous for the carbenium ion's stability. • SO₃-PVI reduces AlCl₃ usage by 33%, lowering corrosion risks in PIB polymerization. • Co-initiator system yields higher molar mass PIBs with broader distributions. • NMR shows exo-olefin end groups rise from 0% to 31%, boosting PIB reactivity. • DFT reveals favorable AlCl₃···O(sulfonate) interactions stabilizing active sites. • SO₃-PVI enables a more efficient and sustainable route to Raffinate-1 polymerization.