Synthesis And Properties Of Thermo-sensitive Polyurethane Materials

As one of the smart polymer materials,the thermo-sensitive polymer can make a reversible response to changes of the external temperature.Thermo-sensitive polymer materials have been widely applied in the biomedical fields such as drug controlled release,biological separation,tissue engineering,immunoassay and so on.At present,the polyurethane with biocompatibility and biodegradability becomes one of the current research hotspots.This paper mainly focuses on the synthesis and characterization of thermo-sensitive polyurethanes and thermally responsive shape memory polyurethane materials.A new class of thermo-sensitive random polyurethanes have been prepared by polymerization of L-lysine ethyl ester diisocyanate with five glycols,and their structures and properties were characterized by FTIR,1H NMR,UV,GPC,and MTT assay.The structure and molecular weight(Mn)of the synthesized 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(LCST),which can be easily tailored in the range of 4.0-35.0? by combination of the monomers.Unexpectedly,the increase of-C H2CH2O-(OEG)in the main-chain of polyurethanes apparently acts as the hydrophobility,totally different from some polymers with OEG in the side-chain.The catalyst-free-synthesized polyurethanes with Mn of about 1 ~ 2 × 104 g/mol response to the external temperature.But,stannous octoate-catalysted polyurethanes with Mn of 3 ~ 6 × 104g/mol exhibit no thermo-sensitivity because of their strong intermolecular H-bonds.In addition,the viability of HeLa cells after 24 and 48 h of incubation indicated good biocompatibility for the polyurethanes.A series of shape memory polyurethane materials were prepared by means of chain extension and crosslinking reaction using with L-lysine ethyl ester diisocyanate and polyethylene glycol as building units.By changing the molecular weight of polyethylene glycol and the feed ratio of L-lysine ethyl ester diisocyanate to polyethylene glycol,the polymerization conditions of the polyurethane with the shape memory properties wereinvestigated.Further studies have shown that several parameters including the molecular weight of soft segment,soft and hard segment ratio,temperature and cycles play a key role in the rate of recovery and recovery time of polyurethane materials.The polyurethane had a good shape memory,and can be fully recovered at 75?,except that the hard content of 20%of the polymer.The higher the recovery temperature,the shorter the response time.In addition,after 10 times of determination,the polyurethane can still return to the initial shape in about 7 min,demonstrating its stable and establishes shape memory.In addition,1,2-propylene glycol,poly(1,2-propylene glycol)-400(PPG-400),poly(1,2-propylene glycol)-1000(PPG-1000),and L-lysine ethyl ester diisocyanate as raw materials,a series of thermo-sentive polyurethanes were synthesized through hydrogen transfer reaction.The chemical structure and thermo-sensitvity of resulting polyurethane were characterized by FTIR,1H NMR and UV spectra.It is found that the thermo-sensitvity of polyurethane materials depend on their chemical structure.Poly(L-lysine ethyl ester diisocyanate-co-PPG-400)and poly(L-lysine ethyl ester diisocyanate-co-PPG-1000)showed excellent thermo-sensitive behavior,their LCSTs were 3.0-25.0?.The molecular weight of polyurethane can be effectively increased by the catalysis of stannous octoate,but its thermo-sensitivity is also reduced.The reason may be that the higher molecular weight or density of carbamate groups can greatly increase the H-bond interactions between macromolecular chains.The biocompatibility and application of thermo-sensitive polyurethane materials are in progress.