Fast and eco-friendly synthesis of new hydrolysable and biodegradable copolyurethanes derived from L-leucine cyclodipeptide and different molecular weights of PEG in TBAB under microwave irradiation

Abstract

In this study novel multi block polyurethane (PU) copolymers containing cyclodipeptide were synthesized under microwave irradiation using a quaternary ammonium salt (QAS) as reaction media. For this, L-leucine cyclodipeptide (LC) was prepared and then a new class of poly(ether-urethane-urea)s (PEUUs) was synthesized in tetrabutylammonium bromide (TBAB) via two-step polymerization method. In the first step, 4,4′-methylene-bis-(4-phenylisocyanate) (MDI) was reacted with LC to produce isocyanate-terminated oligo(imide-urea) as hard segment. The reaction of the aforementioned pre-polymer with poly(ethylene glycols) (PEG) with different molecular weights (PEG400, 600, 1000, and 2000) was the second step to furnish a series of new PEUUs. These PEUUs are thermally stable, soluble in amide-type solvents, hydrolysable, and biodegradable. The resulting PEUUs have inherent viscosities in the range of 0.37–0.67 dL/g. The effects of polymerization method and soft segment length on some of the polymers’ properties and their structural characteristics were compared. The protocol presented here has the merits of environmentally benign, simple operation, convenient work-up, short reaction time and good yields without using volatile organic solvents or catalysts. Ammonium type reaction medium was air and water stable, and relatively cheap, which makes it suitable for applications. The results demonstrate that it can be easily separated and reused without losing activity which makes the method cost effective and eco-benign.