Successful application of an ionic liquid carrying the fluoride counter-ion in biomacromolecular chemistry: microwave-assisted acylation of cellulose in the presence of 1-allyl-3-methylimidazolium fluoride/DMSO mixtures

Surface modification of cellulose nanomaterials with amine functionalized fluorinated ionic liquids for hydrophobicity and high thermal stability

A highly hydrophobic fluorinated ionic liquid (IL), 3-aminopropyl-tributylphosphonium bis(trifluoromethylsolfonyl)imide ([aP4443][NTf2]), was synthesized, and applied for the surface modification of cellulose nanomaterials (CNMs) by reductive amination. The modified CNMs were fully characterized for their chemical structure, morphology, thermal stability, and surface hydrophobicity. Results obtained from Nuclear Magnetic Resonance spectroscopy (1H, 13C, 19F and 31P), Fourier Transform Infrared spectroscopy, X-ray Photoelectron Spectroscopy, and X-ray diffraction confirmed the successful grafting of [aP4443][NTf2] onto the surface of CNMs up to a degree of surface functionalization of 2.5 %. Transmission Electron Microscopy analysis confirmed the dimensions of the CNMs were retained after modification but with significant aggregation for modified cellulose nanocrystals (CNCs). Thermal Gravimetric Analysis demonstrated significant increases in the degradation temperatures of modified CNCs from ∼252 °C to ∼310 °C. Modified cellulose nanofibers (CNFs) did not show any increase in thermal stability. The modified CNM suspensions showed reduced affinity for water and the formation of aggregates in aqueous media. Furthermore, a water contact angle test demonstrated enhanced hydrophobicity for modified CNMs. This modification approach holds potential for the use of the [aP4443][NTf2] IL for functional materials to achieve novel hydrophobic CNMs suitable for aqueous processing with thermoplastics, for fabrication of thermally stable composite materials, and for polymer gel electrolytes for batteries.

Counterintuitive solvation effect of ionic-liquid/DMSO solvents on acidic C-H dissociation and insight into respective solvation

How would acidic bond dissociation be affected by adding a small quantity of a weakly polar ionic liquid IL (the "apparent" or "measured" dielectric constant ε of the IL is around 10-15) into a strongly polar molecular solvent (e.g., ε of DMSO: 46.5), or vice versa? The answer is blurred, because no previous investigation was reported in this regard. Toward this, we, taking various IL/DMSO mixtures as representatives, have thoroughly investigated the effects of the respective solvent in ionic-molecular binary systems on self-dissociation of C-H acid phenylmalononitrile PhCH(CN)₂ via pK _a determination. As disclosed, in this category of binary media, (1) no linear correspondence exists between pK _a and molar fractions of the respective solvent components; (2) only ∼1-2 mol% of weakly polar ILs in strongly polar DMSO make C-H bonds even more dissociative than in neat DMSO; (3) a small fraction of DMSO in ILs (<10 mol%) can dramatically ease acidic C-H-dissociation; and (4) while the DMSO fraction further increases, its acidifying effect becomes much attenuated. These findings, though maybe counterintuitive, have been rationalized on the basis of the precise pK _a measurement of this work in relation to the respective roles of each solvent component in solvation.

Acetylation of Microcrystalline Cellulose by Transesterification in AmimCl/DMSO Cosolvent System

Recently, IL/cosolvent systems have generated a lot of interest as cellulose-dissolving solvents and reaction media for various kinds of cellulose modification. In the present study, both 1-allyl-3-methylimidazolium chloride (AmimCl)/dimethyl sulfoxide (DMSO) and AmimCl/N,N-dimethylformamide (DMF) systems were employed to synthesize cellulose acetate by transesterification. Microcrystalline cellulose, 1,8-diazabicyclo[5.4.0]undec-7-ene and isopropenyl acetate were chosen as the raw material, catalyst and acetylation reagent, respectively. The results revealed that DMSO was a suitable cosolvent for the transesterification in the homogeneous solution. Moreover, DMSO had a positive effect on the reaction as the cosolvent under the given conditions and the degree of the substitution of cellulose acetate could be significantly enhanced through increasing the molar ratio of DMSO. The synthesized products were characterized by Fourier transform infrared (FT-IR) spectroscopy, ¹H and ¹³C nuclear magnetic resonance spectroscopy (¹H-NMR and ¹³C-NMR), correlation spectroscopy (COSY), heteronuclear single quantum correlation (HSQC) spectroscopy, and X-ray diffraction (XRD) to confirm the chemical and physical structure of the cellulose acetate generated. The thermal properties were also evaluated using thermogravimetric analysis (TGA)/derivative thermogravimetry (DTG).