Maleimide Functionalized Siloxane Resins
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developed. Silane coupling agents bearing one functional group capable of forming covalent bonds to silica fillers (e.g., alkoxysilyl) and another to interact through either bonding or nonbonding actions with the organic polymer (e.g., mercapto) are used to chemically bond the filler to the polymer [1]. In order to decrease the filler particle size and to improve filler-polymer interactions, in situ filling by sol-gel polymerization of tetraethoxysilane (TEOS) within the rubber formulation has been extensively investigated [2]. However, this method generally does not permit the necessary loading of filler phase to be dispersed into the composite materials because of phase separation during the in-situ filling process. In this paper we describe the preparation of a new class of inorganic/organic hybrid nanocomposites in which a tailored (Mw, branching, etc.) inorganic filler phase is formed first with coupling agents already in place. The resulting filler can then be copolymerized with organic monomers or polymers by free radical or pericyclic reactions to generate the desired nanocomposite. The silisesquioxane filler phase was prepared by sol-gel polymerization of alkoxysilylmaleimide monomers. Due to the hydrolytic instability of the maleimide, the monomer was first protected by reaction with furan to form the oxonorbomene cycloadduct, prior to sol-gel polymerization. The furan protecting group was removed after polymerization by a thermally induced, retro Diels-Alder reaction. The functionalized silsesquioxane polymer was then copolymerized with styrene to form a filled styrene-maleimide nanocomposite.
15 Mat. Res. Soc. Symp. Proc. Vol. 576 01999 Materials Research Society
EXPERIMENTAL N-(triethoxysilylpropyl)maleimide (1). Compound 1 (Scheme 1) was prepared according to Toru's method for preparing other maleimides [3]. Because of the hydrolytic instability of the ethoxysilyl- groups, workup was modified to avoid the aqueous washing step. 3aminopropyltriethoxysilane (90 g, 0.40 mol) in benzene (100 mL) was added dropwise to a solution of maleic anhydride (40 g, 0.40 mol) dissolved in benzene (1800 mL). The reaction was stirred for 2 h at room temperature. ZnC12 (56 g, 0.40 mol) was added in bulk, the mixture stirred for 30 min and then a solution of hexamethyldisilazane (HMDS, 98 g, 0.60 mol) in benzene (100 mL) was added dropwise. After complete addition of the HMDS, the reaction was refluxed for 2 hours, cooled to room temperature, filtered and filtered again through silica gel. The volatiles
were removed under reduced pressure and the product flash distilled at 90 TC/100 mtorr (yield: 78 g, 64 %). 0 NH 2
(EtO) 3 -.(CH 3 )XSi""ý
+
o
,1O
--
-'
(EtO) 3 -.(CH 3 )xSi
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HO
0
0
O (EtO)3_.(CH3)xSi"
-'
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0 Z"C1,/MDS Heat
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O)3.)CH3)iSi-"
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HO
O
x = 0; Compound 1 x = 1;Compound 2 x = 2; Compound 3
0
Scheme 1. Synthesis of compounds 1, 2 and 3. Diels-Alder Adduct of 1 (4, Figure 2). Compound 1 (77 g, 0.25 mol) and furan (52 g, 0.75 mol) were placed in a Carrius tube, freeze-pump-thaw
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