Synthesis and properties of poly(L‐lactide)‐Poly(Ethylene glycol) multiblock copolymers by coupling triblock copolymers

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Abstract
A series of multiblock copolymers of PLLA/PEG(PLE) with high molecular weight were synthesized by coupling PLLA‐PEG‐PLLA triblock copolymers with succinic anhydride in the presence of N‐dimethylaminopyridine(DMAP) and dicyclohexylcarbodimide (DCC). The results of the viscometry measurement, GPC and 1H NMR, elucidated that multiblock PLE copolymers with high content of short PEG segments had been successfully obtained. The thermal properties and the crystallinity were investigated by DSC and X‐ray diffraction. When LA/EG molar ratio and the length of PEG segments were the same in both multiblock and triblock copolymers, multiblock copolymers were less crystalline than the corresponding triblock ones. Mechanical testing showed that multiblock copolymers had relatively high tensile strength and large elongation. In a word, the measurements showed that this multiblock PLE copolymers had high content of short PEG segments (Mn = 2000,4000), high molecular weight (Mw∼50 000), high hydrophilicity, and good mechanical properties. The drug (5‐Fluorourecil) release behavior of these PLE multiblock copolymers had been studied in 0.10M pH7.4 phosphate buffer solution (PBS), and the releasing rate could be tailored by adjusting copolymers composition. All of these results indicated that the multiblock PLE copolymers might be useful in medical applications. Copyright © 2003 John Wiley & Sons, Ltd.

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