Chemistry Reference
In-Depth Information
Poly(amic acid)s and their ionic salt solutions: Synthesis,
characterization and stability study
ROHIT H. VORA,
1, 2, 3
∗
P. SANTHANA GOPALA KRISHNAN,
1
S. VEERAMANI
1
and SUAT HONG GOH
2
1
Institute of Materials Research and Engineering (IMRE), 3, Research Link, Singapore 117602
2
Department of Chemistry, National University of Singapore (NUS), 10 Kent Ridge Crescent, S8-03,
Science Drive 3, Singapore 117543
3
Department of Materials Science, National University of Singapore (NUS), 10 Kent Ridge
Crescent, S7-03-01, Science Drive 4, Singapore 117543
Abstract—Two series of co-poly(amic acid)s (Co-PAAs) containing various mole percents of
ortho
-Tolidine (o-TDA) and 1,3-bis(3-aminopropyl) tetramethyl disiloxane (SiDA) were prepared
by reacting with 3,3',4,4'-biphenyl tetracarboxylic dianhydride (BPDA) or 3,3',4,4'-benzophenone
tetracarboxylic dianhydride (BTDA) in N-methyl-2-pyrrolidone (NMP) solvent at room tempera-
ture. Subsequently, from these Co-PAAs, we have formulated two series each of the ionic bond type
photodefinable co-poly(amic acid)s (Co-PDPAA), i.e. ionic salts, using N,N-diethylamino ethyl
methacrylate (DEEM) and N,N-dimethylamino ethyl methacrylate (DMEM) respectively. Storage
stability of these solutions at room temperature was monitored for a period of one month by gel
permeation chromatography (GPC), potentiometry and viscometry. Bulk viscosity, inherent viscos-
ity, acid number and molecular weight all decreased drastically as the storage time increased.
Rheological behaviour of Co-PAA and Co-PDPAA in solution was also investigated as a func-
tion of shear rate and temperature. At room temperature, all co-polymer solutions showed shear
thinning behaviour in the shear rate range of 3.07-38.4 s
-1
. The temperature dependence of bulk vis-
cosity followed the Arrhenius equation. The activation energies of viscous flow of BTDA based Co-
PAA and Co-PDPAA were in the range of 25-27 and 22-26 kJ/mol respectively, whereas for BPDA
based Co-PAA and Co-PDPAA were in the range of 12-28 and 19-33 kJ/mol, respectively. Both the
activation energy of viscous flow and ln [A], where A is pre-exponential factor, decreased with an
increase in SiDA content in both Co-PAA and Co-PDPAA series. For a given composition, activa-
tion energy of viscous flow was comparable for both DMEM and DEEM based Co-PDPAA.
Thermal stability of precipitated solids of Co-PAA and Co-PDPAA was investigated using ther-
mogravimetric analyzer (TGA). Both samples showed a two-step weight loss in air atmosphere, the
first step due to imidization and the second step due to degradation. The activation energy for ther-
mal degradation was determined using Coats-Redfern and Chang methods. The activation energy
determined by the two methods was comparable.
Keywords
: Co-poly(amic acid); photodefinable co-poly(amic acid) ionic salt; polyimide storage
stability and degradation.
