Abstract
Recently, thermo-responsive polymers which has lower critical solution temperature (LCST) have been investigated mainly in the biomedical and the separation technologies. However, the thermo- responsive polymers synthesized so far are not biodegradable. Therefore, we tried to synthesize a new biodegradable thermo-responsive polymer derived from polysuccinimide (PSI). PSI shows remarkable hydrolysis and biodegradable properties and can easily introduce various side chains by aminolysis with various amines. Because of peptide bond in main chain, alkylamine-modified PSI (AA-PSI) has a possibility to be a biodegradable polymer. We used isopropylamine, propylamine and so on as aliphatic amines and examined thermal property of aqueous solution of the obtained polymers. The synthesized AA-PSI shows various colloidal properties by changing the introduced alkylamine species and the substitution degree of alkylamine. The aqueous solutions of isopropylamine-modified PSI (IPA-PSI) (the substitution degree : 30-50 %) became turbid in heating process. However even in cooling process, the turbidity did not disappeared. From SEM and DLS measurements, we confirmed the formation of polymer nanospheres which diameter was about 150 nm. We found that imide ring-imide ring interaction stabilized the polymer nanospheres because the turbid solution became clear by the addition of sodium hydroxide solution which cleaved imide ring in IPA-PSI. On the other hand, propylamine-modified PSI (NPA-PSI) which the substitution degree is less than 60 % showed irreversible phase transition, and NPA-PSI which the substitution degree is more than 70 % showed reversible phase transition. This fact supports the stabilization by imide ring-imide ring interaction. Moreover, we obtained IPA-PSI nanospheres encapsulating hemoglobin without denaturation by a simple procedure of heating aqueous IPA-PSI solution dissolving hemoglobin. From these results, it was found that the proposed method provided a new route for preparation of polymeric nanospheres encapsulating protein.
