Polycondensation Using Microwave Heating
We previously reported the polycondensation of 4-
octylaniline with 4,40-dibromoazobenzene;33,34 the reaction
gave the corresponding poly(arylamine), Polymer 1, with a
molecular weight of 18,900 in 95% yield under the optimized
conditions via conventional heating (Scheme 1, Table
1, Entry 1). Accordingly, the investigation regarding the
microwave-assisted reaction began with this polycondensation
reaction, and various fundamental parameters of the
reaction were tested in order to gain insight into the effect
of microwave heating; the results are summarized in Table 1.
In terms of reaction time, microwave heating effectively
reduced the reaction time to about 10 min to give a polymer
with a comparable or higher molecular weight in comparison
with conventional heating (Entries 1 and 3–5). The rapid
and uniform heating by microwave irradiation can probably
cause the high molecular weight of the obtained polymer.
35–40 Owing to these features, the polycondensation reaction
under microwave heating was completed in 10 min,
which could be confirmed by the fact that the reaction conducted
for a longer amount of time (20 min) gave a comparable
result to that obtained in 10 min (Entries 4 and 5).
The reaction was conducted at a lower concentration
(0.1 M) to prevent the precipitation of the polymeric products
during the reaction (Entry 6). However, molecular
weight was slightly decreased under these conditions