Chemistry Reference
In-Depth Information
c
b
d
d
a
c
d
a
b
c
Unreacted end groups
Fig. 6.1
Representative
1
H NMR spectra for disiloxane-polyester (
top
) and silicone-polyester
(
bottom
) synthesized using N435 under solvent free conditions
3.67 ppm which can be assigned as unreacted methyl ester end groups. The methy-
lene protons that are alpha to the carbonyl in CPr-TMDS-DME experience a small
shift up-field after polymerization. The remaining multiplets, 0.54 and 1.64 ppm,
represent the methylene protons that are in the α- and β- positions with respect to
silicon in the monomers and final polymer; the geminal methyl groups on silicon
are resonating at 0.06 ppm and remained largely unchanged throughout the polym-
erization process.
The
13
C NMR spectrum confirms the synthesis of the siloxane polyesters. The
resonance for the carbonyl carbon exhibits a downfield shift and sits at 173.6 ppm
while the
O
-methylene carbon can be found at 66.6 ppm; the carbon adjacent to the
ester linkage was positioned at 37.7 ppm. The remaining resonances were located
at 13.99 and 17.96 ppm have been identified as CH
2
CH
2
Si (in monomer and poly-
mer), and 19.06 and 22.57 ppm has been identified as the
CH
2
CH
2
Si environment.
The
29
Si spectrum possessed two distinct resonances that were located at 7.30 and
7.72 ppm. These signals were in the expected range for disiloxane linkages and do
not represent a possible silanol or alkoxysilane.
FT-IR group assignments were based on assignments previously reported in the
literature [
17
]. There was a strong stretching vibration at 1737 cm
−1
that is typical
of the
νC = O
stretching mode. The vibrational mode associated with the
Si-O-Si
sym
linkage was evident at 1050 cm
−1
. In the polysiloxane the
Si-O-Si
asym
stretch was
evident at 1100 cm
−1
. The absence of peaks at 3350 and 750 cm
−1
(
Si-OH
) sug-
gested there was no enzymatic hydrolysis of siloxane linkages.
