Synthesis and Properties of a New Thermo-sensitive Random Polyurethane with Tunable LCSTs

In this paper, a new class of thermo-sensitive random polyurethanes (PGLDs) have been prepared by polymerization of L-lysineethyl ester diisocyanate with five homologous derivatives of ethylene glycols. The structure and properties of polyurethanes were characterized by various techniques. The molecular weight M-n and structure of polyurethanes are found to be particularly significant factors to their thermo-sensitivity. Four polyurethanes except poly(L-lysine ethyl ester diisocyanate-co-ethylene glycol) show a reversible phase transition at the lower critical solution temperature, which can be easily tuned in the range of 4-35 degrees C by combination of the monomers. Unexpectedly, the increasing number of -CH2CH2O-units in the main-chain of polyurethanes apparently acts as the hydrophobicity in the solution. The catalyst-free-synthesized polyurethanes with M-n of about (1-2) x 10(4) g/mol responses to the external temperature. Stannous octoate-catalysted polyurethanes with M-n of (3-6) x 10(4) g/mol exhibit no thermo-sensitivity because of their strong intra/intermolecular interactions. In addition, the viability of HeLa cells in 0.01-100 g/mL solution reached to 80% after 24 and 48 h of incubation, indicating no cytotoxicity for polyurethanes.