Different Solvent Free Synthetic Routes to Organic/Inorganic Hybrid Materials
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H. KADDAMI"2, J.F. GERARD 1 , J.P. PASCAULT 1 SLaboratoire des Matrriaux Macromolrculaires, BAtiment 403, UMR 5627, 20 avenue Albert Einstein, 69621 Villeurbanne Cedex, France, [email protected] 2 Universit6 Cadi Ayyad, FSTG, BP 618, Gueliz, Marrakech, Marocco
ABSTRACT
The sol-gel chemistry in low-temperature conditions can be used to produce organicinorganic materials nanocomposite from the in-situ formation of silica-rich phase in a polymer matrix. Different synthetic routes have been proposed: i) hydrolysis and condensation reactions of silane end capped oligomers, ii) polymerization of hydroxyethyl methacrylate, HEMA in presence of preformed functionalized silica nanoparticles, and iii) simultaneous hydrolysis and condensation of tetraethoxysilane and polymerization of hydroxyethymeth-acrylate. Rheological investigations made during the polymerization of these three systems display many differences. Time for gelation was chosen as the time at which the loss factor, tan6 is independent on the testing frequency, or the time at which the system displays an elastic response. Vitrification phenomenon is associated with a tan6 peak. In some cases vitrification of the inorganic-rich phase interfered with the observation of gelation and the appearance of a non soluble fraction in a good solvent like tetrahydrofurane can help for attribution. During radical chain-polymerization of HEMA a classical Trommsdorff-effect was observed. It can be at the same time than the macrogelation in the case of neat HEMA or delayed by the presence of grafted SiO 2 nanoparticles. During simultaneous synthesis of inorganic and organic phases, vitrification of the inorganic-rich phase occured just after macrogelation of the system. Final morphologies are strongly dependent on the occurrence of these different structural
transformations. Key-words Hybrid chemistry, phase separation, gelation, vitrification, Trommsdorff-effect. INTRODUCTION
Polymerization of organic and/or inorganic monomers in low-temperature conditions can be used to produce organic-inorganic (0/I) materials. Different solvent free synthetic routes can be proposed:
(1) Hydrolysis and condensation reactions of silane-end capped oligomers prepared by one or two stages (1-3) H20 - Si(OR)3 10 O0/1I (1) SP catalyst Hydrolysis and condensation reactions of alkoxysilane are usually named sol-gel chemistry. The disadvantage of this route is that the concentration of inorganic clusters remains low, i.e. 2-3 wt %, due to the low concentration of chain ends. It can be increased by the introduction of an additional alkoxysilane monomer such as tetraethoxysilane, TEOS. 51 Mat. Res. Soc. Symp. Proc. Vol. 576 © 1999 Materials Research Society
(-
(2) Polymerization of an organic monomer in presence of preformed silica nanoparticles 13 nm in diameter) which can be functionalized (4-7) initiator M
+
M' -
i
-
T
0/I
(2)
Different chemistries can be used. A peroxyde will initiate the radical-chain polymerization of M and M' double-bonds.
(3) Simultaneous hydrolysis / conden
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