Rapid synthesis of new block copolyurethanes derived from L -leucine-PEG in ionic liquids under microwave irradiation

摘要

This study concerns the synthesis of novel multi block polyurethane (PU) copolymers containing eco-friendly segments, taking the advantage of ionic liquids (IL)s under microwave irradiation. For this, L-leucine anhydride cyclodipeptide (LAC) was prepared and then a new class of poly(ether-urethane- urea)s (PEUUs) was synthesized with two types of ILs, including room temperature imidazolium (RTIL)s and molten ammonium type ILs. ILs were used as reaction media and PUs were prepared via two-step polymerization method. Polymerization reaction was also conducted under conventional heating method in N-methyl pyrrolidone (NMP) as reaction solvent. In the first step, 4,4′-methylene- bis(4-phenylisocyanate) (MDI) was reacted with LAC to produce isocyanate-terminated poly(imide-urea) oligomers as hard segment. Chain extension of the resulting prepolymer with polyethyleneglycol (PEG) of molecular weights of 400 (PEG-400) was the second step to furnish a series of new PEUUs. These multiblock copolymers are optically active, thermally stable and soluble in amide-type solvents. PEUUs prepared in ILs under microwave irradiation showed more phase separation and crystallinity than PEUU prepared under conventional method. Some structural characterization and physical properties of these PEUUs, prepared under different methods, are reported and compared.