PubMed · 15233251
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Lee Kirsch. Lessons unlearned.. https://pubmed.ncbi.nlm.nih.gov/15233251/
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Self-assembly of poly(ethylene oxide)-block-poly(epsilon-caprolactone) five-arm stars (PEO-b-PCL) was studied at the air/water (A/W) interface. The block copolymers consist of a hydrophilic PEO core with hydrophobic PCL chains at the star periphery. All the polymers have the same number of ethylene oxide repeat units (9 per arm), and the number of epsilon-caprolactone repeat units ranges from 0 to 18 per arm. The Langmuir monolayers were analyzed by surface pressure/mean molecular area isotherms, compression-expansion hysteresis experiments, and isobaric relaxation measurements, and the Langmuir-Blodgett (LB) films' morphologies were investigated by atomic force microscopy (AFM). PCL homopolymers crystallize directly at the A/W interface in a narrow surface pressure range (11-15 mN/m). In the same pressure region, the star-shaped block copolymers undergo a phase transition corresponding to the collapse and the crystallization of the PCL chains as shown by the presence of a pseudoplateau in the isotherms. The LB films were prepared by transferring the Langmuir monolayers onto mica substrates at various surface pressures. AFM imaging confirmed the formation of PCL crystals in the LB monolayers of the PCL homopolymers and of the copolymers, but also showed that the PCL segments can undergo additional crystallization after monolayer transfer during water evaporation. The PCL crystal morphologies were also strongly influenced by the surface pressure and by the PEO segments.
The aim of this study was to define a block copolymer micellar system with a high solubilization capacity for poorly soluble aromatic drugs. Ethylene oxide and phenyl glycidyl ether were sequentially polymerized to form the diblock copolymer G5E67 (G = phenyl glycidyl ether, OCH2CH(CH2OC6H5); E = oxyethylene, OCH2CH2; subscripts denote number-average block lengths in repeat units). The association properties in aqueous solution over the range 20-50 degrees C were investigated by surface tensiometry and light scattering, yielding values of the cmc, hydrodynamic radius, and association number; gel boundaries in concentrated micellar solution were investigated by tube inversion. The solubilization capacity of G5E67 for the poorly water-soluble drug griseofulvin was higher than that of a triblock EGE copolymer of longer G block length and considerably higher than that achieved with poloxamers (EmPnEm, P = oxypropylene).
Micellar solutions of EmPnEm copolymers may be mobile at ambient temperature and form hard gels on warming to body temperature, whereas micellar solutions of EmSnEm copolymers do not show this effect (E denotes oxyethylene, P oxypropylene and S oxyphenylethylene, and subscripts m and n denote chain lengths). The aim of this study was to combine the desirable gelation characteristics of solutions of the EmPnEm copolymers with the greater solubilising capacities of solutions of the EmSnEm copolymers. Accordingly, the gelation characteristics in aqueous solution of binary mixtures of the triblock copolymer E62P39E62 (Pluronic F87) with E137S18E137, E82S9E82 or E76S5E76 were investigated by rheological techniques. We have shown that 50/50 wt.% mixtures of E62P39E62 with either E137S18E137 or E82S9E82 at a total copolymer concentration of approximately 30 wt.% are fluids of low viscosity at temperature below 22-25 degrees C and gels of high elastic modulus at body temperature.The mixed systems have potential as vehicles for the controlled delivery of solubilised drug from gels formed in situ following subcutaneous injection of a low viscosity aqueous solution.