Reversible Gelation in Semidilute Aqueous Solutions of Associative Polymers:  A Small-Angle Neutron Scattering Study

Abstract

Thermally reversible gelation in 1% aqueous solutions of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)-g-poly(sodium acrylate) has been observed. The transition that occurs as the temperature is increased through the gelation threshold (T gel) is clearly observable by rheological and small-angle neutron scattering (SANS) measurements. SANS measurements suggest that within the hydrogel there exists an unusually uniform matrix of scattering centers, attributed to close packing of micelle-like aggregates surrounded by highly hydrated poly(sodium acrylate) and unassociated ethylene oxide/propylene oxide copolymer. The physical cross-linking caused by these scattering centers induces gelation. Direct model fits to the SANS data suggest that the scattering centers are similar in structure, but somewhat smaller than micelles of the poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) component, with a dehydrated poly(propylene oxide) core of radius 30 Å surrounded by a hydrated PEO corona of outer radius 60 Å.

Interactions among proteins and hydrophobically modified polyelectrolytes

“…Indeed, Pluronic-PAA interacts strongly with co-ionic surfactants such as alkyl sulfates . It has been shown that alkyl chains of surfactant can be incorporated into the micelles of Pluronic-PAA, cores of which consist primarily of poly(propylene oxide) (PPO) (Huibers et al 1999). The micelles form in Pluronic-PAA solutions at temperatures above 20mC (Bromberg 1998a-e) polymer domains thus creating gels.…”

“…We have recently discovered a new class of PAA-based copolymers and gels, whereby PAA is modified with a triblock copolymer of poly(ethylene oxide) (PEO) and poly-(propylene oxide) (PPO) (Pluronic, or Poloxamer), which is attached to PAA via carbon-carbon bond (Bromberg 1998a-e ;Bromberg & Ron 1998 ;Bromberg & Barr 1999 ;Bromberg & Magner 1999 ;Bromberg & Salvati 1999 ;Bromberg & Temchenko 1999 ;Bromberg 2001a, b). The copolymers of PAA and Pluronics (termed Pluronic-PAA herein) possess properties beneficial for topical delivery that complement mucoadhesion of PAA, such as the ability to self-assemble in aqueous solutions forming micelle-like aggregates (Bromberg 1998c, d ;Huibers et al 1999). The Pluronic-PAA micelles are capable of solubilizing hydrophobic drugs in aqueous solutions (Bromberg & Temchenko 1999).…”

Thermosensitive Self-Assembling Block Copolymers as Drug Delivery Systems

“…Furthermore SANS studies [121] demonstrated that micelle-like aggregates formed in Pluronic-PAA solutions above the CMT are unusually uniformly distributed.…”

Synthesis and Self-Assembly of Poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)-g-poly(acrylic acid) Gels

“…The copolymers of PAA and polyethers resulting from the novel synthetic route possess a micelle-forming capability and have been used in topical drug delivery and pharmaceuticals. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] Previously, the synthesis of such polymers was specifically optimized to avoid the formation of permanently cross-linked, water-insoluble networks produced within a polymer particle during the polymerization of AA. 19 Conversely, in the present study we aimed at increased yield of such networks, contemplating temperature-sensitive PAA latexes.…”