Gelation of Concentrated Micellar Solutions of a Triblock Copolymer of Ethylene Oxide and Styrene Oxide, S5E45S5

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Abstract

Triblock copolymer S5E45S5 was synthesized by oxyanionic polymn. of styrene oxide initiated by a preformed difunctional polyethylene glycol. Here E denotes OCH2CH2, S denotes OCH2CH(C6H5), and the subscripts denote no.-av. block lengths in repeat units. Previous work on the closely related copolymer S4E45S4 indicated that micelles would form in aq. solns. of copolymer S5E45S5, and that they would undergo transient intermicellar bridging. Dynamic light scattering was used to confirm this. Rheometry and small-angle x-ray scattering were used to explore gel boundaries, structures, and properties. At moderate copolymer concns. (14 and 20 wt. %) measurements of the dynamic shear moduli indicated the formation of low-modulus soft gels attributed to spherical micelles forming transient networks. A region of low storage modulus at c ??????? 30 wt. % preceded a change to hard gel. A 40 wt. % hard gel was disordered, while at higher concns. (49 and 60 wt. %) the micelles packed into hexagonal structures with high values of the storage modulus (G' ??????? 10 kPa at 25 ????C and 1 Hz). [on SciFinder(R)]

Keyword(s)

Cloud point; Loss modulus; Micelles; Phase diagram; Storage modulus (gelation and mech. properties of concd. micellar solns. of ethylene oxide-styrene oxide triblock copolymer) ; ethylene oxide triblock copolymer concd soln storage modulus micelle; styrene oxide triblock copolymer concd soln gelation

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