Preparation of Amazingly Hard polyHIPE material from a Direct Emulsion
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Preparation of Amazingly Hard polyHIPE material from a Direct Emulsion Carlos Youssef 1, Rénal Backov 2, Mona Treguer 3, Marc Birot 1, Hervé Deleuze 1* 1
Université de Bordeaux, Institut des Sciences Moléculaires, UMR-CNRS 5255, 351 cours de la Libération, 33405 Talence, France. 2 Université de Bordeaux, Centre de Recherche Paul Pascal, UPR 8641-CNRS, 115 Avenue Albert Schweitzer, 33600 Pessac, France. 3 Université de Bordeaux, Institut de Chimie de la Matière Condensée, UPR 9048-CNRS, 87 Avenue Albert Schweitzer, 33608 Pessac, France. ABSTRACT Interconnected microcellular polymeric monoliths having unexpected high mechanical strength have been prepared using the High Internal Phase Emulsion methodology. Direct concentrated emulsions of aqueous 5-amino-1-vinyl-[1,2,3,4]tetrazole mixed with low molar (5 %) fractions of N,N’-methylenebisacrylamide (MBA) as cross-linking agent were prepared using dodecane as dispersed phase and a mixture of hydrophilic surfactants. “Reverse” polyHIPE materials were obtained after radical copolymerization, solvent extraction and drying. Their morphology, chemical composition and physico-chemical behaviour are discussed. INTRODUCTION Emulsion templating is a simple and versatile method for the preparation of microcellular materials (cell size range 2–100 µm) by polymerizing the continuous phase of a high internal phase emulsion (HIPE). The obtained materials have been called polyHIPEs by Unilever researchers. [1] Theoretically, the final solid polymer is expected to have an open-cell morphology only for a sufficiently concentrated HIPE (dispersed phase volume fraction > 74 % of the total emulsion). [2-3] However, this structure has been observed for lower values. [4] The historic polyHIPE preparation involves the formation of a stable, inverse concentrated emulsion using hydrophobic monomers as part of the continuous phase (most generally a mixture of styrene and divinylbenzene with, optionally, the addition of a functionalized styrene such as 4vinylbenzyl chloride) and an aqueous phase as the dispersed phase. A great deal of work coming from a continuous increasing number of researchers has been devoted to the study of this particular system. [5-10] The main topics studied have been the good control of the porous morphology (voids and interconnecting windows size dispersion), [11-16] and attempts to increase the mechanical strength of the material which, in its native formulation, is usually considered as insufficient for practical applications. [17-19] Several efforts have been made as well on the use of hydrophobic (meth)acrylate derivatives. [20-21] Much less work has been published on the synthesis of polyHIPE based on hydrophilic (i. e. water-soluble) monomers emulsified by an hydrocarbon. Krajnc and coworkers reported the preparation of the so-called “reverse” polyHIPE by polymerization of an oil-in-water HIPE consisting of an aqueous mixture of acrylic acid and N,N’-methylenebisacrylamide (MBA) as continuous phase and toluene as dispersed phase. [22] Superabsorbent
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