Synthesis Of A Novel Thermo-sensitive Polymer Containing Serine Moieties And The Performance Study Of Its Aqueous Solution

A novel water-soluble thermo-sensitive polymer containing serine moieties was designed and synthesized in this work. Different from traditional temperature -sensitive materials'volume phase transition, the synthetic polymer takes the pH value of its aqueous solution as the response signal to temperature changing. Structures of the products were confirmed by FTIR and 1H NMR. The response mechanism of pH value to temperature of the polymer aqueous solution was investigated preliminarily.Two functional monomers of N-acryloyl-1,2-diaminoethane hydrochloride and 2-aminoethyl methacrylate hydrochloride were synthesized by group protection and de-protection. N-t-butoxycarbonyl-1,2-diaminoethane was prepared from the reaction of di-tert-butyl dicarbonate (Boc₂O) and excess ethylenediamine, then reacted with acryloyl chloride and N-t-butoxycarbonyl-N'-acryloyl-1,2- diaminoethane was obtained. The resultant were de-Boc-protected to give N- acryloyl-1,2-diaminoethane hydrochloride, yield 65%. N-t-butoxycarbonyl- ethanolamine was obtained in the same way, then reacted with methacryloyl chloride in the presence of triethylamine as acid acceptor in THF media at 0⁵℃, then N-t-butoxycarbonyl-aminoethyl methacrylate was obtained. The 2-aminoethyl methacrylate hydrochloride (AMA) was obtained by deprotection of the above product, yield 79%. The monomer was polymerized in aqueous solution with V-50 as initiator, and the water-soluble functional poly (aminoethyl methacrylate hydrochloride) (PAMA) was synthesized.N-t-butoxycarbonyl-serine was prepared by amino protection of L-serine, then reacted with N-Hydroxysuccinimide (HOSu), in the presence of N,N'- dicyclohexylcarbodiimide (DCC) as dehydrating agent and give a serine active ester (N-Boc-Ser-OSu). The serine moieties was introduced to the PAMA pendant group and the novel water-soluble thermo-sensitive poly(aminoethyl methacrylate hydrochloride)-g-serine (PAMA-g-Ser) was obtained by grafting small molecules onto the polymer chains.The pH response to temperature of PAMA-g-Ser aqueous solution with different initial pH values was investigated by determination of the solution pH value using acidimeter while temperature increased from 30℃to 60℃. The influence of initial pH value on its pH^T responsivity was studied preliminarily, and the response mechanism was proposed. Results showed that the pH of PAMA-g-Ser aqueous solution decreased with temperature increasing while its initial pH value was constant. And the pH^T responsivity varied with different initial pH values of PAMA-g-Ser aqueous solution. While the temperature increased from 30℃to 60℃, the solution pH value decreased by 0.96, 0.18 and 0.11 respectively with the initial pH values of the aqueous solution 6.69, 3.79 and 3.39. That is the pH^T response sensitivity was higher when there was a higher initial pH value. And the pH^T response sensitivity decreased when there was HCl aqueous solution existing and the initial pH value of the solution was lower. The solution pH value decreased unobviously with temperature increased.