title: Synthesis and characterization of PEO-PCL-PEO triblock copolymers: effects of the PCL chain length on the physical property of W(1)/O/W(2) multiple emulsions.
abstract: A series of poly(ethylene glycol)-block-poly(epsilon-caprolactone)-block-poly(ethylene glycol) (PEO-PCL-PEO) triblock copolymers were prepared and then used for the investigation of the effects of the ratio of epsilon-caprolactone to poly(ethylene glycol) (i.e., [CL]/[EO]) on the physical properties of water-in-oil-in-water (W(1)/O/W(2)) multiple emulsions containing a model reagent, ascorbic acid-2-glucoside (AA2G). In the synthesis, the [CL]/[EO] was varied from 0.11 to 0.31. The molecular weights and compositions of PEO-PCL-PEO were determined by GPC and (1)H NMR analyses. Thermal behavior and crystal formation were studied by DSC, XRD, FT-IR, and polarized optical microscopy (POM). Aggregate behavior of PEO-PCL-PEO was confirmed by DLS, UV, and (1)H NMR. Morphology and relative stiffness of the W(1)/O/W(2) multiple emulsions in the presence of PEO-PCL-PEO were studied by confocal laser scanning microscopy (CLSM) and rheometer. Variation in the [CL]/[EO] significantly affects the crystalline temperature and spherulite morphology of PEO-PCL-PEO. As the [CL]/[EO] increases, the CMCs of PEO-PCL-PEO decreases and the slope of aggregate size reduction against the copolymer concentration becomes steeper except for the lowest [CL]/[EO] value of PEO-PCL-PEO (i.e., P-222). P-222 significantly increases the viscosity of continuous (W(2)) phase, which implies the copolymer would exist in the W(2) phase. On the other hand, the triblock copolymers with relatively high [CL]/[EO] ratios mainly contribute to the size reduction of multiple emulsions and the formation of a firm wall structure. The particle size of the multiple emulsion decreases and the elastic modulus increased as [CL]/[EO] increases, confirmed by microscopic and rheometric analyses.
authors.affiliation: College of Engineering, Kyungpook National University, 1370 Sankyuk-3-dong, Buk-gu, Daegu 702-701, South Korea.
authors.forename: Heui Kyoung
authors.initials: HK
authors.lastname: Cho
authors.forename: Kwang Soo
authors.initials: KS
authors.lastname: Cho
authors.forename: Jin Hun
authors.initials: JH
authors.lastname: Cho
authors.forename: Sung Wook
authors.initials: SW
authors.lastname: Choi
authors.forename: Jung Hyun
authors.initials: JH
authors.lastname: Kim
authors.forename: In Woo
authors.initials: IW
authors.lastname: Cheong
mesh_terms: D002152:Calorimetry, Differential Scanning; D004655:Emulsions / Q000737:chemistry*; D008853:Microscopy; D009821:Oils / Q000737:chemistry; D011091:Polyesters / Q000138:chemical synthesis / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000138:chemical synthesis / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D004655:Emulsions; D009821:Oils; D011091:Polyesters; C502908:poly(ethylene glycol)-poly(caprolactone)-poly(ethylene glycol); D014867:Water; D011092:Polyethylene Glycols