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Effects of Solvent Compositionon the Assembly andRelaxation of Triblock Copolymer-Based Polyelectrolyte Gels.

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Title: Effects of Solvent Compositionon the Assembly andRelaxation of Triblock Copolymer-Based Polyelectrolyte Gels.
Authors: Henderson, Kevin J.1, Shull, Kenneth R.1
Source: Macromolecules. Feb2012, Vol. 45 Issue 3, p1631-1635. 5p.
Subjects: Block copolymers, Polyelectrolytes, Hydrogels, Micelles, Polymers, Macromolecules
Abstract: The role of solvent selectivity has been explored extensivelywithregard to its role in the phase behavior of block copolymer assemblies.Traditionally, thermally induced phase separation is employed forgenerating micelles upon cooling a block copolymer dissolved in aselective solvent. However few amphiphilic, polyelectrolyte-containingblock copolymers demonstrate a thermally accessible route of micellization,and solvent exchange routes are frequently employed instead. Here,we describe the use of mixed solvents for obtaining thermoreversiblegelation behavior of poly(methyl methacrylate)-poly(methacrylic acid)-poly(methylmethacrylate) (PMMA–PMAA–PMMA) triblock copolymers.One solvent component (dimethyl sulfoxide) is a good solvent for bothblocks, and the second solvent component (water) is a selective solventfor the polymer midblock. Rheological frequency sweeps at variablesolvent compositions and temperatures demonstrate an adherence totime–temperature–composition superposition, so thatchanges in the solvent composition are analogous to changes in theFlory–Huggins interaction parameter between end block and solvent.Shift factors used for this superposition are related to the effectiveactivation energy describing the viscosity and stress relaxation responseof the triblock copolymer gels. The effectiveness of solvent exchangeprocesses for producing hydrogels with this system is shown to originatefrom the ability of a small amount of added water to greatly increasethe relaxation times of the self-assembled polymer gels that are formedby this process. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
Description
Abstract:The role of solvent selectivity has been explored extensivelywithregard to its role in the phase behavior of block copolymer assemblies.Traditionally, thermally induced phase separation is employed forgenerating micelles upon cooling a block copolymer dissolved in aselective solvent. However few amphiphilic, polyelectrolyte-containingblock copolymers demonstrate a thermally accessible route of micellization,and solvent exchange routes are frequently employed instead. Here,we describe the use of mixed solvents for obtaining thermoreversiblegelation behavior of poly(methyl methacrylate)-poly(methacrylic acid)-poly(methylmethacrylate) (PMMA–PMAA–PMMA) triblock copolymers.One solvent component (dimethyl sulfoxide) is a good solvent for bothblocks, and the second solvent component (water) is a selective solventfor the polymer midblock. Rheological frequency sweeps at variablesolvent compositions and temperatures demonstrate an adherence totime–temperature–composition superposition, so thatchanges in the solvent composition are analogous to changes in theFlory–Huggins interaction parameter between end block and solvent.Shift factors used for this superposition are related to the effectiveactivation energy describing the viscosity and stress relaxation responseof the triblock copolymer gels. The effectiveness of solvent exchangeprocesses for producing hydrogels with this system is shown to originatefrom the ability of a small amount of added water to greatly increasethe relaxation times of the self-assembled polymer gels that are formedby this process. [ABSTRACT FROM AUTHOR]
ISSN:00249297
DOI:10.1021/ma201607m