Thin films of crosslinked polymethylhydrosiloxane (PMHS) have been grafted on silica using the sol-gel process allowing further functionalization by effective quantitative hydrosilylation of SiH groups by olefins within the network. Postfunctionalization gives the polysiloxane network with n-alkyl side chains. The PMHS coating was prepared by room temperature polycondensation of a mixture of methyldiethoxysilane HSiMe(OEt) 2 monomer and triethoxysilane HSi(OEt) 3 (TH) as crosslinker. The surface-attached films are chemically stable and covalently bonded to the silica surface. Subsequently, films were functionalized without delamination. We showed by FTIR spectroscopy how the crosslinking ratio and the molecular size of the alkenes precursors influence the extent of the hydrosilylation reaction of SiH groups in the PMHS network. We have determined that quasi-full olefin addition catalyzed by a platinum complex occurred within soft networks of less than 5% TH with 1-alkenes CH 2 ¼ ¼CH(CH 2 ) n-2 CH 3 of various alkyl chain lengths (n ¼ 5, 11, 17). Powders of PMHS gel were also modified with 1-alkenes by hydrosilylation. The SiH groups within the soft gel (5% crosslinked) were fully functionalized as shown by 29 Si and 1 H solid-state NMR. The structure of functionalized polysiloxane with n-octadecyl and n-dodecyl side chains was studied by FTIR, wide angle X-ray diffraction, and DSC showing crystallization of the long n-alkyl chains in the network. V V C 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: [3546][3547][3548][3549][3550][3551][3552][3553][3554][3555][3556][3557][3558][3559][3560][3561][3562] 2008
Crosslinked polymethylhydrosiloxane (PMHS) thin films prepared by sol-gel polycondensation have been functionalized by Pt-catalyzed hydrosilylation of SiH groups with an allyl ureido crown ether precursor. To this purpose, both 4 0 -allylurea-benzo-15-crown-5 (1) and 1-allyl-3-propyl-urea (2) were synthesized and characterized. We have shown that competitive side-reactions occurred following hydrosilylation due to the hydrolysis of part of the SiH groups resulting in the formation of new crosslinks Si(CH 3 )O 3/2 as shown by solidstate 29 Si-NMR. This is explained by the deactivation of the Pt catalyst toward hydrosilylation by amide groups. For thin films ($ 1 lm) prepared on silicon wafers, a quantitative method based on FT-IR transmission spectroscopy was used to measure the crosslinking density of the network, and the percentage of functionalization (SiC %) following hydrosilylation. The results are discussed in relation to the mesh size of the network, and the diffusion of alkenes and water molecules within lightly crosslinked PMHS gels obtained by varying the amount of triethoxysilane crosslinker (mol %) from 15 to 1%. The self-organization properties of ureido groups by H-bonding were studied by FT-IR for the functionalized thin films. The complexation properties of the crown ether 1-functionalized thin films were evidenced by using FT-IR following diffusion-reactions of NaSCN and KSCN salts in CHCl 3 : MeOH solvent mixtures within thin films.
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