Sol-Gel Chemistry by Ring-Opening Polymerization
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63 Mat. Res. Soc. Symp. Proc. Vol. 576 © 1999 Materials Research Society
Scheme I M i4e Si
0. -MeMe Me, Me-SI M/ Me Me
TBAH THF or with 4s Me--S( Me•S
c~,,i5 ýMe :MeMe 1
TBAH = Bu4NOH
Me Me
M
EXPERIMENTAL Monomer synthesis. Scheme 2 shows the synthetic scheme for preparation of phenylene-bridged have been fully characterized and experimental details disilaoxacyclopentane, 1. All compounds 5 have been published elsewhere.[ ] Polymer syntheses. Polymerization of 1 can be achieved either neat as a melt polymerization using octadecylamine as catalyst, or as a solution in THF (1M) using Bu 4NOH (TBAH) as catalyst. Rapid polymerization of 1 can be achieved when polymerized as a copolymer system with 4, using TBAH as catalyst. Scheme 2. Synthetic scheme for monomer 1. MeQ
QMe
11N.
:•
H+/H 20, CH2CI2 Pd(P(Ph) ) ,
MeO / Me
34 Me reflux temp., 2, 4 Si 2(OMe)
M2
-4 MeOH
24Hr
Me....,0 A yMe Me ,--Me
MeI--M •
Me
de-i
•
MeO
OMe2
Me., .,O..,Me Me-F '-Me
e H2 , Pd/C CH2 C12 Me-
Me- -SK'oSMe Mer-S Me 3
Si:z:Me1
RESULTS AND DISCUSSION Monomer 1 can readily be polymerized in THF or when dissolved in monomer 4 (used as a solvent/co-monomer) to give transparent, yellow-tinted gels (scheme 1). Furthermore, because the copolymer of 1 and 4 is prepared without solvent, total shrinkage is kept to less than 5% compared with 50-90% for traditional sol-gels. Since the resulting gels are insoluble, solid state NMR and infrared spectroscopy are used in their characterization. 29 Si NMR confirmed the opening of the disilaoxacyclopentane rings with the pronounced upfield shift in the two observed resonances; 21.9 and 20.9 ppm for 1 in solution and 9.8 and 5.5 ppm for the homopolymer in the solid state. This upfield shift is consistent with the release of ring strain in the five membered ring with ROP.J61 The small peak at 22 ppm, in the solid state 29Si NMR spectrum, is attributed
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to the residual amounts of unreacted pendant disilaoxacyclopentane groups. Ring opening is further confirmed when comparing the IR spectra of 1 and its homopolymer; the resonance at 920.7 cm 1 due to the cyclic SiOSi stretch in 1 is replaced by the broad resonance at 1061.8 cm-1 due to acyclic SiOSi stretches in the homopolymer.
0 U'
L1
u'rr"r 11 T.
I-
1 h W4
r"l l I'""l
-2
3)
22
02
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-2
22
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Figure 1. 29 Si NMR spectra for monomer 1 and its homopolymer. NMR resonances for I (left spectrum) are 21.9 and 20.9 ppm and those for the polymer (right spectrum) are 9.8 and 5.5 ppm. Exothermic copolymerization of a mixture of 4 and 1 (80:20 by weight) with TBAH (0.17 mol% based on dislaoxacyclopentane groups) gives rise to a transparent, crack-free gel within seconds of mixing. Higher catalyst concentration (0.83 mol% based on disilaoxacyclopentanes) leads to generation of enough heat during polymerization to cause a few small bubbles to form (presumably due to monomer volatilization) and become entrapped within the resulting gel. Solid state 13C and 29Si NMR revea
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