SYNTHESIS of BIODEGRADABLE COLYMER OF LACTIC ACID HAVING THIOL GROUPS AND EVALUATION OF ITS CHARACTERIZATION

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To modify the properties of poly(lactic acid)[poly(LA)] and to introduce pendant thiol groups to poly(LA), the random terpolymer of L-LA, glycolic acid(Glc) and cysteine(Cys) {poly[LA-random-(Glc-Cys)]} was synthesized through ring-opening and copolymerization of L-lactide with cyclodepsipeptide cyclo{Glc-Cys(MBzl) and subsequent deprotection of methoxybenzyl groups. By changing the mol fraction of (Glc-Cys) unit, the solubility, thermal transition, degradation behavior of the modified poly(LA), and the water contact angle of its film could be varied. Moreover, to achieve high accumulation of thiol groups located on the surface of copolymer film, the synthesis of AB-type diblock copolymer of L-lactide (L-LA) and depsipeptide with pendant thiol groups were investigated. Cyclo[Gls-Cys(MBzl)] was polymerized in tetrahydrofran (THF) solution using potassium ethoxide as an initiator. The terminal hydroxyl group of the poly[Glc-Cys(MBzl)] obtained was converted to potassium alkoxide by K/naphthalene. L-LA was polymerized in THF using the polymer alkoxide as a macroinitiator to obtain poly[Glc-Cys(MBzl)]-block-polyLA showing two melting temperatures (Tms). Through subsequent deprotection of methoxybenzyl groups, the biodegradable amphiphilic AB-type block copolymer, poly(Glc-Cys)-block-polyLA, was obtained. The accumulation ability of thiol groups located on the surface of block copolymer film was evaluated to be higher than that of the random copolymer film.