Membrane Gas Separation

3.2
Experimental 
Synthesis of PTMSN is described in detail elsewhere [12] . The monomer was prepared 
from dicyclopentadiene and vinyltrimethylsilane by a Diels – Alder reaction. Polymerization 
was performed in toluene solution in the presence of nickel naphthenate [(Nph) 
2
Ni] as a 
catalyst and methylalumoxane (MAO) as co - catalyst. A vast surplus of MAO resulted in 
higher molecular mass of the polymer (up to 440 000 Da) which led to better fi lm - forming 
properties and less brittleness of the fi lms. The fi lms of the polymers studied were cast 
from the 2 – 3 mass % solution in toluene (or cyclohexane in the case of non - substituted 
addition - type polynorbornene studied for comparison). Before testing, the fi lms were kept 
in a vacuum until a constant weight is attained (for about 1 week). The thickness of the 
fi lms was in the range 100 – 200
μ
m. Two methods were used in the determination of the 
transport parameters. Permeability ( P ) and diffusion ( D ) coeffi cients were determined 
using gas chromatographic and mass spectrometric methods. In the former technique the 
steady 
- 
state stream of penetrant gases under atmospheric pressure fl ew around the 
upstream part of the fi lm, while the downstream part of it was moved around by the gas 
carrier – helium or nitrogen (the latter was used in the measurement of permeation rate 
of H 
2
and He). The permeability coeffi cients were determined by measuring the penetrant 
concentration in the gas carrier and the total fl ow of this mixture. The determination of 
the diffusion coeffi cients D involved an adjustment of the experimental sigmoid - type 
curve of the attaining of the steady - state stream across the tested fi lm and the theoretical 
one computed for the case of Fickian diffusion [18] . Measurements were performed in 
the range 20 – 60 ° C. In the mass spectrometric set - up the permeability is measured by the 
slope of the increase in a certain ion current in the mass spectrum of the diffusing gas 
molecule after attaining steady - state conditions. The diffusion coeffi cient was determined 
using the Daynes – Barrer method. The measurements were carried out at 22 ° C and pres-
sure 0.1 – 1 atm over the fi lm and about 10 
– 4
mmHg below the fi lm, i.e. in the receiving 
volume of the mass spectrometer. The details of the investigation of PTMSN using the 
positron annihilation lifetime spectroscopy (PALS) and inverse gas chromatography 
(IGC) can be found in Refs. 12 and 13.