Effect of Copolymer Architecture on the Micellization and Gelation of Aqueous Solutions of Copolymers of Ethylene Oxide and Styrene Oxide

Abstract

The micellar properties and solubilization capacity of poorly water soluble drugs of several micellar and gel solutions of diblock and triblock copolymers of styrene oxide/ethylene oxide have been measured and compared with block copolymers of butylene oxide/ethylene oxide, showing that the solubilization capacity of the styrene oxide block is approximately four times that of a butylenes oxide block for dilute solutions. To continue establishing the correlation between micellar characteristics and solubilization capacity, we have found it interesting to compare the micellar and gelation properties of the diblock and triblock copolymers PSO10PEO135 and PEO69PSO8PEO69 (subindexes are the number-average block lengths), with different architecture but similar average block lengths. Surface tension measurements allowed the determination of the critical micelle concentrations at several temperatures and, so, to calculate standard enthalpies of micellization. Static and dynamic light scattering data permitted us to determine micellar parameters and to obtain qualitatively the extent of hydration of the copolymer micelle. A tube inversion method was used to define the mobile-immobile (soft-hard gel) phase boundary. To refine the phase diagram and observe the existence of additional phases, rheological measurements were done. The results are in good agreement with previous values published for PSOnPEOm and PEOmPSOnPEOm copolymers.

Tuning the gelation of thermoresponsive gels

“…The easiest gel formation by the diblock copolymers was attributed to more stable micelles formed by these due to the low micellisation enthalpy. 63 In another study AB, ABA as well as a BAB copolymer were compared, based on EO and BO and the results were similar to the above with the two triblocks not forming a gel while the AB diblock copolymer did. 65 In a study by the same authors using the same monomers but by increasing the hydrophobic content gelation was achieved by the triblock copolymers too however the CGC increased from the diblock to the ABA triblock to the BAB; indicating once again the easier gelation of the diblock compared to the corresponding triblock copolymers.…”

“…63,64 The polymers in the first study were based on EO and styrene oxide (SO), 63 and in the second study on EO and BO 64 with the hydrophobic monomers SO and BO being always the B block. The easiest gel formation by the diblock copolymers was attributed to more stable micelles formed by these due to the low micellisation enthalpy.…”

Surface Tension, Density and Viscosity Studies on the Associative Behaviour of Oxyethylene-Oxybutylene Diblock Copolymers in Water at Different Temperatures

“…After getting the surface tension data for about thirty dilutions for each copolymer solution at a given temperature, the plots of surface tension (γ) versus logC (where C is the concentration of copolymers the in g·dm -3 ) were used for estimation of the critical micelle concentration, CMC of the polymer. The CMC, was assigned to the concentration at and above which the surface tension remain constant [3,21,[26][27][28].…”

“…The relative magnitude of these two opposing effects, therefore, determines whether the CMC increases or decreases over a particular temperature range [27]. In most cases of nonionic surfactants, increase in temperature favour micellization and aggregation process while opposite situation can be seen in case of ionic amphiphiles because the solubility of ionic surfactant enhances at higher temperature and repulsion between the ionic head groups may occur [4,7,16,[26][27][28][29][30][31][32][33][34][35][36][37][38]. In case of PEO-PBO block copolymers, it is expected that higher is the content of hydro- 19 at a given temperature ( Table 2).…”

Poly(ethylene oxide)–poly(styrene oxide)–poly(ethylene oxide) copolymers: Micellization, drug solubilization, and gelling features

“…To overcome some of these limitations, more hydrophobic block copolymer counterparts with similar architecture, but with the PPO segment replaced by a more hydrophobic one, such as poly(butylene oxide) (PBO), poly(styrene oxide) (PSO) or phenylglycidyl ether (PG), have been developed by the Attwood and Booth's group in collaboration with us during last years [17][18][19][20][21]. Polystyrene oxide-based block copolymers are of particular interest due to (i) their ability to self-assemble at very low concentrations into micelles with improved solubilization ability and stability [22,23] and (ii) the low glass transition temperatures (ca.…”