Hydrocarbon-Bridged Polysiloxane and Polysilsesquioxane Network Materials.
- PDF / 979,615 Bytes
- 5 Pages / 414.72 x 648 pts Page_size
- 13 Downloads / 183 Views
Me
I
0 ýS i-O
•Si-L, A
S n
7Me -
O•
B
n
Figure 1. Bridged Polysilsesquioxane (A) and Polysiloxane (B) Structures. In this study, we examine the effect of reducing the number of potential siloxane network bonds at the monomers' termini. A new class of silicon polymers, hydrocarbon-bridged polysiloxanes (Figure 1), were prepared. Two types of bridging groups were chosen for this study. The first bridging group was the flexible 1, 6-hexylene (Scheme 1, monomers 1 and 2) [3]. The second bridging functionality employed was the rigid 1,4-phenylene group (Scheme 2, monomers 3 and 4) that has been utilized extensively in bridged polysilsesquioxane systems. Hexyleneand phenylene-bridged polysiloxanes (X-2 and X - 4, §This research was supported by the United States Department of Energy under contract No. DE-AC04-94AL85000.
487 Mat. Res. Soc. Symp. Proc. Vol. 346. 01994 Materials Research Society
Figure 2) were prepared by sol-gel processing of 1, 6-bis(diethoxymethylsilyl)hexane 2 and 1, 4-bis(diethoxymethylsilyl)benzene 4, respectively. On each silicon, one site available for polycondensation in polysilsesquioxane monomers 1 and 3 has been replaced with a terminal methyl group. The result (B, Figure 1) is a crosslinked siloxane network with a total of four siloxane linkages to each monomer repeat unit instead of the six in the bridged polysilsesquioxanes (A, Figure 1). The objective of this study was to determine 1). if bridged polysiloxanes would form as gels under the conditions used to prepare bridged polysilsesquioxane gels and 2). the effect of lower crosslink density, if any, on the porosity of the resulting dried gels (xerogels). Herein we describe the synthesis of monomers 1-4, their hydrolysis and condensation to afford xerogels, and their characterization by solid state NMR spectroscopy and nitrogen sorption porosimetry.
I
Me
Me Si~sIII
Me
Ni
--
Me
I
0
00 n X-4
X-2
Figure 2. Hexylene- and Phenylene-Bridged Polysiloxanes.
EXPERIMENTAL Hexylene monomers were prepared by the chloroplatinic acid-catalyzed hydrosilation of 1, 5-hexadiene with triethoxysilane [3] to give 1, or with diethoxymethylsilane to give 2. The pure monomers can be obtained by distillation at reduced atmosphere: 1, b.p. = 105-108 'C @ 25 mtorr; 2, b.p. = 113-116 'C @ 200 mtorr. The phenylene monomers were prepared by Barbier(EtO) 3 -xMexSiH
e
(EtO) 3 _xMexSiS0
SSi(OEt) 3_xMex D
rl 2 r L2%t.A 6 Uol 2 k.)
PhH
1,2
Scheme 1. Hydrosilation of hexadiene (1, x = 0; 2, x = 1) Grignard reactions from 1, 4-dibromobenzene and tetraethoxysilane to afford 3, or methyltriethoxysilane to afford 4 [1], again as high-boiling liquids: 3, b.p. = 130-135 'C @ 200 mtorr; 4, b.p. = 102-104 'C @ 17 mtorr.
(EtO)4 _xMexSi Br--&/-Br
(EtO) 3_xMexSi
\
Si(OEt) 3 _xMex
Mg
THF
3,4
Scheme 2. Barbier-Grignard Preparation of monomers 3 (x = 0) and 4 (x = 1).
488
Sol-gel hydrolysis-polycondensation of monomers 1-4 were carried out under identical conditions. In all cases the amount of monomer calculated to make a 0.4 M solution was placed
Data Loading...
