A. Al‐Saden

Poloxamer association in aqueous solution

Abstract Aqueous solutions of the surface active poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) block copolymers (poloxamers) were studied using photon correlation spectroscopy (quasi-elastic light scattering) and viscosity measurements. Poloxamers 184 and 237 showed detectable aggregates at 25° only at concentrations above about 6% with size increasing with concentration and with significant polydispersity, probably indicating a multiple association process. At 35°, however, essentially invariant values for the hydrodynamic radius were found over a wide concentration range and the systems were essentially monodisperse: these systems are more likely to be represented by a closed association model. The more hydrophilic poloxamer 188, however, retained its concentration dependence of aggregate size up to 55°. The variation with temperature of both the hydrodynamic radius of aggregates and the intrinsic viscosity of several poloxamers was rationalized by relating the temperature-dependency curves to the cloud point of the poloxamer. In some cases only certain sections of the curve are observable when the cloud point is high, e.g., >100°, or low, e.g.,

Characterization of mixed nonionic surfactant micelles by photon correlation spectroscopy and viscosity

Abstract Mixed micelles of the nonionic surfactants Brij 92 and Brij 96 were shown to be large and asymmetric. Using the relationship between the radius of gyration (from total intensity light-scattering dissymmetry measurements) and the hydrodynamic radius (from photon correlation spectroscopy) the mixed micelles are shown to have a rod-like structure, the length of which increases with temperature and on addition of salt. These rod-like micelles appear to exhibit considerable flexibility which is responsible for their measured viscosities being less than that expected from their asymmetry.

Cross-linked hydrophilic gels from ABA block copolymeric surfactants

Abstract Gelation of aqueous solutions of poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) block co-polymeric non-ionic Surfactants (Pluronics or poloxamers) by the action of γ-rays is reported. Poloxamers with ethylene oxide content below 70% do not gel under the conditions studied, but appear to undergo chain scission, as there is a decrease in cloud point and an increase in hydrodynamic radius which is most likely to be due to increased association of the more hydrophobic polymer. The gels obtained from poloxamers with ethylene oxide content over 70% have a high water uptake capacity. The possibility of using these gels as sustained release drug delivery systems is discussed.

Poly(oxyethylene) chain scission following γ-irradiation of triton X-100 and other commercial non-ionic surfactants☆

Abstract γ-Irradiation of micellar solutions of non-ionic surfactants (e.g. Triton X-100, Triton X-405 and Cetomacrogol 1000) has been found to lead to poly(oxyethylene) chain scission rather than to poly(oxyethylene) chain cross-linking as has been found for poly(oxyethylene) of high molecular weight. Viscosity, surface tension, cloud point, solubilisation and nuclear magnetic resonance measurements, together with light scattering techniques (both total intensity and photon correlation spectroscopy) support the conclusion that poly(oxyethylene) chain scission occurs with the non-ionic surfactants investigated leading to the formation of mixed micelles.

NOVEL POLOXAMER (PLURONIC) AND POLOXAMINE (TETRONIC) HYDROGELS: Swelling and Drug Release

Hydrogels have attracted widespread attention for a variety of biomedical applications (Andrade 1976). i n a cobalt-60 source failed because the ethylene oxide chain of the surfactants studied degraded upon irradiation (Al-Saden et a1 izing gel which might retain some of the solubilizing capacity of the individual micelles in the surfactant solutions. We have since succeeded in cross-linking poloxamer (Pluronic) ABA block copolymeric surfactants and now report the cross-linking of related poloxamine (Tetronic) block copolymers with the general formula

THE γ-IRRADIATION OF TRITON X-100 AND THE PROPERTIES OF MIXED MICELLES OF NON-IONIC SURFACTANTS

one of the reasons for such studies was to confirm what appeared to be degradation of the polyoxyethylene chain during gamma ( Y )-irradiation of aqueous solutions of Triton X 1 0 0 . that polyoxyethylene chains were cross-linked by Y-irradiation, it was hoped that intramicellar cross-linking of the polyoxyethylene chains would occur. However, the properties of the Y-irradiated aqueous solutions are very similar to those of the mixed micellar systems of Tritons of varying polyoxyethylene &ain length. We have studied by light scattering,