Περίληψη:
Copolymers of ethylene oxide and 1,2-butylene oxide (E18B10, E43B9, E40B10, E90B10, E96B18E184B18, E = oxyethylene unit, B = oxybutylene unit, subscripts denote number-average chain lengths) with B blocks terminated by hydroxy groups (denoted EmBnH)were methylated to provide copolymers having the same chain length and composition but with B blocks terminated by methoxy groups (denoted EmBnM). Micelle properties of the M copolymers were determined by dynamic and static light scattering (hydrodynamic radius, association number, thermodynamic radius) and the values obtained compared with those for the H copolymers, most of which had been published previously. The results for copolymer E18B10M in solution at 40°C were consistent with the formation of worm-like micelles, the micelles of the other copolymers being spherical, including E18B10H in solution at 40°C and E18B10M in solution at 30°C. For micelles of the B18 copolymers, methylation reduced the values of all properties by ca. 10%. For micelles of the B9-B10 copolymers, the effect of methylation was to reduce the hydrodynamic radius by ca. 10%, but to increase the association number by ca. 25% and thermodynamic radius by ca. 10%. The explanation of these effects takes into account the increased hydrophobicity of the methylated B blocks, the highly stretched state of the B18 blocks in their micelles, and the probability that water will concentrate at the centre of the cores of micelles of copolymers with hydroxy-ended B blocks. For copolymers forming spherical micelles, the effect of methylation on association number is equivalent to raising the temperature of the solution by ca. 10°C. For micelles of copolymer E18B10, the effect of methylation is to lower the temperature of the sphere-to-worm transition from 40-50° (E18B10H) to 30-40°C (E18B10M).
Συγγραφείς:
Kelarakis, A.
Mai, S.-M.
Havredaki, V.
Mark Nace, V.
Booth, C.
Λέξεις-κλειδιά:
1,2 epoxybutane; copolymer; ethylene oxide; hydroxyl group; oxygen derivative; unclassified drug, article; chemical composition; hydrodynamics; hydrophobicity; light scattering; mathematical model; methylation; micelle; reduction; temperature; thermodynamics
