Chemistry Reference
In-Depth Information
2
2
+2
6L
6L
6L
2+
6L
2
6L
2
2
2
2
Q
Q RUa
1
&&
KUV
2
6L
6L
6L
2
2
2
5
2
2
6L
6L
5
P
Q
2
2
Scheme 6.1
The synthesis of siloxane-containing polyesters using enzymatic catalysis. Polyesters
were produced under solvent-free conditions over 24 h time periods
acyl acceptor, the ratio of the N435 to CPr-TMDS-DME was maintained so that
the catalyst loading would not change. This has not been typically done in previ-
ous enzyme-mediated polymerizations. However, due to the large mass difference
in our two substrates it was prudent to control for this aspect of the reaction. The
initial rate of polymer elongation and total monomer conversion were monitored
by removing 10-15 μL of the reaction mixture at predetermined time intervals and
performing analysis by
1
H nuclear magnetic resonance spectroscopy (NMR). At
the end of the reaction cycle, the reaction was stopped by the addition of 5 mL of
diethyl ether or chloroform when necessary. The enzyme beads were removed via
filtration and the final polymer was characterized by NMR, Fourier-transform infra-
red spectroscopy (FT-IR), and differential scanning calorimetry (DSC).
As each N435-mediated reaction progressed the viscosity of the reaction mixture
increased and the original mixture transformed from clear and colourless to slightly
opaque after 24 h. Control reaction performed in the absence of any catalyst did not
show any polymerization after the 24 h reaction cycle indicating that the enzyme
catalyst was responsible for the polymerizations.
6.3
Structural Characterization of Siloxane-Containing
Polyesters
The structural environments of the siloxane-derived polyesters were probed pri-
marily through NMR and FT-IR spectroscopies. Typical
1
H NMR spectra for the
disiloxane and polysiloxane polyesters are presented in Fig.
6.1
. There is a triplet
positioned at 4.039 ppm in the disiloxane polyester and 4.052 ppm in the silicone
polyester which represents the methylene protons alpha to the oxygen atom in the
newly formed ester linkage between the disiloxane-containing monomers; in the
monomer this resonance is located at 3.60 ppm. There is a smaller singlet located at
