Chemistry Reference
In-Depth Information
A new interpretation of the kinetic model for the
imidization reaction of PMDA-ODA and BPDA-PDA
poly(amic acid)s
CHANG-CHUNG YANG, KUO HUANG HSIEH and WEN-CHANG CHEN
∗
Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan
Abstract—In this study, a new interpretation is given for the imidization of poly(amic acid)s based
on the Seo model:
k
(
t
) =
b
×
sech(-
at
). The parameters
a
and
b
in the original Seo model are the rate
constant of the imidization reaction and the invariant constant, respectively. However, according to
the equation
k
(
t
) =
b
×
sech(-
at
),
k(t)
approaches
b
at the initial time,
t→
0. The assumption that the
parameter
b
is independent of temperature conflicts obviously with the fact that the rate constant of
first-order reaction
k(t)
is a function of temperature. In this study, the activation energies of
a
and
b
were proposed as the energy barriers for the transition state and the rate constant of the imidization
reaction, respectively. The new interpretation was tested by imidizing two commercially available
poly(amic acid)s: PMDA-ODA and BPDA-PDA from 120 to 225°C. The extent of imidization was
determined by a comparison of the intensity of the 1380 cm
-1
peak in the FTIR spectra. The experi-
mental results suggested that the activation energy from the new interpretation was similar to the lit-
erature reports. However, the activation energy from the original Seo model was significantly dif-
ferent from the literature values reported.
Keywords
: Poly(amic acid); imidization; kinetic model.
1. INTRODUCTION
Thermally stable polyimides have been used as a dielectric material since 1970
[1-6]. Generally, poly(amic acid)s were prepared first followed by spin coating
and curing to complete the imidization reaction, as shown in eq. (1):
(1)
Kinetic studies on the imidization reaction of poly(amic acid)s have been ex-
tensively carried out [7-23]. A first-order reaction was always used to describe the
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