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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 35, Number 8
BKCSDE 35(8)
August 20, 2014 

Synthesis and Micellar Characterization of CBABC Type PLGA-PEO-PPO-PEO-PLGA Pentablock Copolymers
Haseob Seong, Eun-Bum Cho*, Joongseok Oh, Taihyun Chang*
Poly(lactic acid-co-glycolic acid), Pluronic F68, Pentablock copolymer, PLGA-F68-PLGA, Ring-opening polymerization
Poly(lactic-co-glycolic acid) (PLGA) were grafted to both ends of Pluronic® F68 ((EO)75(PO)30(EO)75) triblock copolymer to produce poly{(lactic acid)m-co-(glycolic acid)n}-b-poly(ethylene oxide)75-b-poly(propylene oxide)30-b-poly(ethylene oxide)75-b-poly{(lactic acid)m-co-(glycolic acid)n} (PLGA-F68-PLGA) pentablock copolymers. Molecular weights of PLGA blocks were controlled and five kinds of pentablock copolymers with different PLGA block lengths were synthesized using in-situ ring-opening polymerization of D,L-lactide and glycolide with tin(II) 2-ethylhexanoate (Sn(Oct)2) catalyst. PLGA-F68-PLGA pentablock copolymers were characterized by ¹H- and ¹³C-NMR, GPC, and TGA. The numbers (2m, 2n) of repeating units for lactic acid and glycolic acid inside PLGA segments were obtained as (48, 17), (90, 23), (125, 40), (180, 59), and (246, 64), with 1H-NMR measurement. From NMR data, the resultant molecular weights were determined in the range of 12,700-29,700, which were similar to those obtained from GPC. Polydispersity index was increased in the range of 1.32-1.91 as the content of PLGA blocks increased. TG and DTG thermograms showed discrete degradation traces for PLGA and F68 blocks, which indicate the weight fractions of PLGA blocks in pentablock copolymers can be calculated by TG profile and it is possible to remove PLGA block selectively. Hydrodynamic radius and radius of gyration of pentablock copolymer micelle were obtained in the range of 46-68 nm and 31-49 nm, respectively, in very dilute (i.e. 0.005 wt %) aqueous solution of THF:H2O = 10:90 by volume at 25 oC.
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