462 Maya et al.
Macromolecules, Vol. 35, No. 2, 2002
nitrogen inlet, and dropping funnel were added 1.27 g (0.0120
mol) of BrCN and 6 mL of acetone. The mixture was cooled at
-30 °C. A solution of 0.00569 mol of the corresponding siloxane
phenol, 1.21 g (0.0120 mol) of Et3N, and 2 mL of acetone was
transferred to the dropping funnel and added dropwise to the
BrCN solution while a -20 °C reaction temperature was
maintained. The resulting suspension was stirred 1 h at -20
°C and 1 h while warming to room temperature. The suspen-
sion was rapidly filtered and washed with 3 mL of CH2Cl2.
The filtrate was concentrated under vacuum without heating.
The oil obtained was dissolved in 10 mL of CH2Cl2 and
extracted three times with 10 mL of HCl (1%) and three times
with 10 mL of distilled water. The organic phase was dried
over anhydrous MgSO4. Filtering and vacuum rotary evapora-
tion yielded the corresponding dicyanate as amber oil. IR and
1H NMR of the n ) 1 member indicated significant quantities
of the diethylcyanamide byproduct present.4 It was removed
by Kugelrohr vacuum distillation (60 °C/1 Torr).
1,3-Bis(3′-(2-cya n a top h en yl)p r op yl)-1,1,3,3-tetr a m eth -
yld isiloxa n e (Si2-Cy). Isolated yield: 1.11 g (41%) oil; nD
1.5097; mp 5.35 °C. 1H NMR (300 MHz, CD3COCD3) δ: 0.049
(s, 12H, CH3), 0.60 (m, 4H, CH2), 1.66 (q, 4H, CH2), 2.71 (t,
4H, CH2), 7.31-7.49 (m, 8H, Harom). 13C NMR (75 MHz, CD3-
COCD3) δ: 0.412 (CH3), 18.57, 24.73, and 33.37 (CH2), 109.6
(OCN), 115.3, 127.8, 128.9, 131.5, 132.4, and 152.2 (Carom). IR
(NaCl) ν: 2959 (C-H), 2261 (OCN), 1595, 1492, and 1453 (C-
C), 1259 (Si-CH3), 1168 and 1136 (SiOSi), 1078 cm-1 (Si-C).
1,5-Bis(3′-(2-cya n a t op h en yl)p r op yl)-1,1,3,3,5,5-h exa -
m eth yltr isiloxa n e (Si3-Cy). Isolated yield: 1.61 g (51%) oil;
nD 1.5086; mp 8.56 °C. 1H NMR (300 MHz, CD3COCD3) δ:
0.008 (s, 6H, CH3), 0.65 (s, 12H, CH3), 0.62 (m, 4H, CH2), 1.70
(q, 4H, CH2), 2.71 (t, 4H, CH2), 7.29-7.50 (m, 8H, H-arom).
13C NMR (75 MHz, CD3COCD3) δ: -0.636 and 0.503 (CH3),
17.65, 23.88, and 32.54 (CH2), 109 (OCN), 114.43, 127, 128.14,
130.70, 131.67, and 151.45 (Carom). IR (NaCl) ν: 2966 (CH),
2255 (OCN), 1582, 1492, and 1453 (C-C), 1259 (Si-CH3), 1162
and 1059 (SiOSi), 800 cm-1 (Si-C).
F igu r e 2. IR spectra of allylphenol, tetramethyldisiloxane,
Si2-PhOH precursor, Si2-Cy monomer, and cured Si2-
CyResin.
intermediates were characterized by IR, 1H, and 13C
NMR spectroscopies (see Experimental Section), and the
IR spectrum of Si2-bisphenol is included in Figure 2.
The corresponding spectra show the disappearance of
the Si-H group (2128 cm-1; 4.8 ppm) and conversion
of the -CH2-CHdCH2 group (1615 cm-1; 6.1 and 5.2
ppm) to the -(CH2)3- group (2.65, 1.65, 0.60 ppm; 19,
24, 34 ppm).
1,7-Bis(3′-(2-cya n a t op h en yl)p r op yl)-1,1,3,3,5,5,7,7-oc-
ta m eth yltetr a siloxa n e (Si4-Cy). Isolated yield: 1.98 g
1
(55%) oil; nD 1.4847; mp -12.23 °C. H NMR (300 MHz, CD3-
COCD3) δ: 0.019 and 0.072 (2xs, 24H, CH3), 0.63 (m, 4H, CH2),
1.69 (q, 4H, CH2), 2.72 (t, 4H, CH2), 7.31-7.50 (m, 8H, Harom).
13C NMR (75 MHz, CD3COCD3) δ: 0.282 and 1.328 (CH3),
18.51, 24.75, and 33.42 (CH2), 110.0 (OCN), 115.3, 127.9, 129.0,
131.4, 132.5, and 152.3 (Carom). IR (NaCl) ν: 2959 (w, CH2),
2261 (OCN), 1576, 1492, and 1453 (C-C), 1153 (Si-CH3), 1162
and 1039 (SiOSi), 800 cm-1 (Si-C).
The second step is the cyanation of the bisphenol
intermediates. A modification of the Grigat and Pu¨tter
reaction conditions18 was used as previous experience
has shown altering the order of reagent mixing such
that the phenol is prereacted with the triethylamine
reduced byproduct formation.19 Also, 5% excesses of the
triethylamine and cyanogen bromide are used to ensure
that the phenol is completely converted to the cyanate.
This causes diethylcyanamide to form as a byproduct,
but it is far easier to separate from the product than is
unreacted phenol.19 The three cyanate ester macromono-
mers (Si2-Cy, Si3-Cy, Si4-Cy) were characterized by
IR, 1H, and 13C NMR spectroscopies, and the IR
spectrum of Si2-Cy is presented in Figure 2. In addition
to the bands associated with the dimethylsiloxane
structure (1168 and 1136 cm-1 Si-O-Si stretching;
1078 cm-1 Si-C stretching and CH3 rocking; 1259 cm-1
Si-CH3 deformation), the triple bond stretching of the
cyanate group appears as a strong unsplit band at 2261
cm-1. The unsplit character of this cyanate band is a
unique feature for this aromatic cyanate ester series.
For all other known aromatic cyanate esters the band
in this region is split into two or more resolved bands.3
The origin of this splitting is not understood although
unsuccessful attempts have been made to correlate it
with electronic substituent effects.20,21 In this case it
may be possible that the ortho substitution of the large
trimethylenesiloxane group may have a steric influence.
In the NMR diagnostics for the phenol to cyanate
Resin Cu r e P r oced u r e. The dicyanate monomers (Si2-
Cy, Si3-Cy, and Si4-Cy) were cured with a copper naphth-
enate-nonylphenol catalyst solution.16 The dicyanate mono-
mers was initially degassed at 100 °C/1 Torr for 10 min
followed by addition of 2.3 phr of catalyst solution (0.31 g of
copper naphthenate in 3.00 g of nonylphenol) and degassed
again a second time (100 °C/1 Torr/10 min). The hot degassed
molten resin was transferred to an appropriate mold and cured
according to the schedule 175 °C (12 h) f 225 °C (2 h). The
cured resins are ejected from the mold and cut/polished where
necessary for a uniform surface and thickness. All castings
are dark amber in appearance.
Resu lts a n d Discu ssion
Mon om er Syn th esis. The sequence of reactions in
the synthesis of the oligodimethylsiloxane linked cyan-
ate ester macromonomers is depicted in Figure 1.
The first step is the chloroplatinic acid catalyzed
hydrosilylation of 2-allylphenol with the corresponding
hydride terminated dimethysiloxane to yield the respec-
tive siloxane bisphenols. This reaction has been reported
to work remarkably well with an unexpected accelera-
tion in rate correlated with the presence of the phenol
functional group.17 In our hands, this reaction proceeded
well but not quite quantitatively, and distillation was
necessary to separate residual unreacted phenol. These