Chemistry Reference
In-Depth Information
3.5
110
100
3.0
90
80
2.5
70
2.0
60
50
1.5
40
1.0
30
20
0.5
10
0.0
0
01234567890 1
Reaction cycle
Fig. 6.7
A single batch of N435 was used for ten 24 h reaction cycles at 100 °C. The
DP
avg
(
open
circles
) and monomer conversion (
black circles
) are shown
tolerance of a single batch of the immobilized enzyme catalyst. A series of 24 h
reaction cycles at 100 °C were performed using a single batch of N435. The change
in the reaction rate and monomer conversion was used as metrics to determine the
effect of repeated long term reaction cycles. Between each consecutive use of the
catalyst, the reaction mixture was cooled to room temperature and washed with
diethyl ether to cleanse the acrylic beads of any residual polymer. The acrylic beads
were recovered by filtering through a medium porosity glass fritted filter.
The change in the rate of polymer elongation and total monomer conversion for
each of 10 successive uses of the same batch of N435 is presented in Fig.
6.7
. With
the exception of the first three trials in which the apparent rate constant remained
fairly constant, each successive reaction cycle led to some loss in the catalytic pro-
ficiency of the enzyme. The rate decreases by approximately 50 % after six reaction
cycles and by the tenth reaction cycle more than 80 % of the initial enzyme activity
has been lost. Despite this loss, when the polymerizations continued for the full 24 h
reaction cycle, monomer conversion reached high levels, typically in the range of
80-93 %.
These results can be compared to a previous study where a single batch of N435
was used for the ring opening polymerization (ROP) of ε-caprolactone in toluene at
70 °C over several 4 h reaction cycles [
22
]. N435 was shown to have lower activity
in the first reaction cycle compared to subsequent reaction cycles. It was postulated
that swelling of the acrylic resin allowed for any lipase on the interior of the solid
support to become available to the medium and participate in the ROP of PCL.
