Chemistry Reference
In-Depth Information
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Fig. 6.2
The change in the apparent rate constant (h
−1
) with increasing temperature. Two differ-
ent acyl acceptors were used, one derived from a disiloxane (
white bars
) and the other from a
polysiloxane (
grey bars
). Each bar is the average of three independent trials; error bars indicate
the standard deviation
6.4
Elongation Kinetics
Polyester synthesis is a second order process [
18
]. The rate of polymer elongation
can be determined using a plot of the average degree of polymerization (DP
avg
) ver-
sus time, where DP
avg
= 1/(1 −
p
) in which
p
is the extent of monomer conversion.
The slope of the line can be taken as the apparent rate of polymer elongation. Mono-
mer conversion was determined using the integration values from
1
H NMR that
correspond to the
O
-methylene protons of the diol before and after esterification.
6.4.1
CPr-TMDS and 3HP-TMDS
When polyesterifications were performed in the temperature range 35-70 °C, the
rate of polymer elongation was slow (Fig.
6.2
). Increases in temperature to 100 °C,
increased the polymerization rate to 1.94 h
−1
. This increase is attributed to the in-
creasing proficiency of the enzyme coupled with the ease of removal of the meth-
anol by-product. It was hypothesized that temperatures above 100 °C would be
deleterious to the functioning of the enzyme as a result of thermal denaturation.
However, this was not the case (see Sect. 6.7). In fact the apparent rate constant
