NAMS 2002 Workshop - ICOM 2008

Gas Separation V – 5
Friday July 18, 11:45 AM-12:15 PM, Kaua’i
Synthesis and Gas Permeability of Hyperbranched Polyimide Membranes
K. Nagai (Speaker), Meiji University, Kawasaki, Japan - nagai@isc.meiji.ac.jp
The mobility of polymer chains is larger for their polymer terminal chain ends as
compared to that for their polymer main chains. Therefore, gas-induced
plasticization may occur easily around the polymer chain ends as compared to
around the polymer main chains. Moreover, if the number of polymer chain ends
is minimized in a membrane, gas-induced plasticization would be prevented. In
order to reduce the number of polymer chain ends as well as their mobility,
hyperbranched polymer membranes were prepared, and the plasticization
resistance of their carbon dioxide (CO2) permeability was investigated. The base
polymers for hyperbranch were the polyimides based on 4,4'-
(hexafluoroisopropylidene)diphthalic anhydride (6FDA). The diamine used for
these polyimides was either 3,4-diaminodiphenyl ether (3,4DADE) or 2,3,5,6tetramethyl-1,4-phenylene
diamine (TeMPD). Both chain ends of the linear
6FDA- based polymer were capped with either 4-(2- phenylethynyl)phthalic
anhydride (PEPA) or p- aminostyrene. For example, in the case of 6FDA-
3,4DADE-PEPA, the hyperbranch structure was formed by the cycrotrimerization
of three acetylene groups in three PEPA groups in the presence of tantalum
chloride (V), which act as a catalyst. The linear base polyimide was soluble in
chloroform and so on, while the hyperbranched one showed poor solubility in the
same solvents. In addition, the hyperbranched polyimides had larger membrane
density than their base linear counterparts. During CO2 exposure at 40 atm and
at 35C, the CO2 permeability coefficient in the base linear polyimide membranes
increased with time, whereas in the hyperbranched one, the polyimide
membranes were stable, indicating resistance for CO2 plasticization.