Synthesis of poly(oxymethylene) dimethy ethers catalyzed by acidic functionalized ionic liquids

Poly(oxymethylene) dimethyl ethers (PODE n, n>1) were synthesized by the condensation of trioxymethylene (TR) and methanol (MeOH) over the functionalized ionic liquids like HnmpHSO₄, HnmpH₂PO₄, HnmpPTSA and PyN(CH₂)₃SO₃HHSO₄; the effects of the catalyst amount, raw materials ratio, temperature, pressure and time on the reaction behaviors were investigated. The results showed that the catalytic activity of ionic liquid is related to its acidity. PyN(CH₂)₃SO₃HHSO₄ exhibits the highest catalytic activity; under the optimum reaction conditions, i.e. PyN(CH₂)₃SO₃HHSO₄ amount of 2.0%, molar ratio of MeOH to TR of 2.0, 110 ℃, 2.0MPa and reaction time of 6h, the conversion of TR and selectivity to PODE_3~8 reach 97.69% and 32.54%, respectively. Moreover, the ionic liquid PyN(CH₂)₃SO₃HHSO₄ can be spontaneously separated from product phase after the reaction.