Kunlun Hong

Effect of Ionic Liquid Treatment on the Structures of Lignins in Solutions: Molecular Subunits Released from Lignin

The solution structures of three types of isolated lignin--organosolv (OS), Kraft (K), and low sulfonate (LS)--before and after treatment with 1-ethyl-3-methylimidazolium acetate were studied using small-angle neutron scattering (SANS) and dynamic light scattering (DLS) over a concentration range of 0.3-2.4 wt %. The results indicate that each of these lignins is comprised of aggregates of well-defined basal subunits, the shapes and sizes of which, in D(2)O and DMSO-d(6), are revealed using these techniques. LS lignin contains a substantial amount of nanometer-scale individual subunits. In aqueous solution these subunits have a well-defined elongated shape described well by ellipsoidal and cylindrical models. At low concentration the subunits are highly expanded in alkaline solution, and the effect is screened with increasing concentration. OS lignin dissolved in DMSO was found to consist of a narrow distribution of aggregates with average radius 200 ± 30 nm. K lignin in DMSO consists of aggregates with a very broad size distribution. After ionic liquid (IL) treatment, LS lignin subunits in alkaline solution maintained the elongated shape but were reduced in size. IL treatment of OS and K lignins led to the release of nanometer-scale subunits with well-defined size and shape.

CHAPTER 1:Polymerization in Ionic Liquids

The use of ionic liquids (ILs) as a medium for polymerization is a rapidly growing field. While much of the initial interest in this area was from a Green Chemistry perspective (using non-volatile ILs to replace polluting VOCs), a major impact on polymerization chemistry was quickly noted. Now, nearly all major types of polymerization have been reported in ILs. Advantages of conducting polymerization in ILs include increases in polymerization rate and molecular weight, diminished termination rates, facilitation of block copolymer synthesis, and advantageous bi-phasic polymerization systems allowing facile catalyst recovery and re-use. This chapter provides a review of the relevant literature in this rapidly growing area.