Poly[ (tetrafluoropropoxy) 2-x (trifluoroethoxy) x ]phosphazenes of different substituent ratio were synthesized via nucleophilic substitution of polydichlorophosphazene (PDCP) which was prepared by vacuum thermal ring-opening polymerization of hexachlorocyclotriphosphazene (HCCP) .The final substituted polyphosphazene products were purified through the THF-benzene precipitation.31 P-NMR was used to assure the purification.The polymer structure was characterized by 1H-NMR and FTIR.The glass transition temperature was detected by differential scanning calorimetry (DSC) .The molecular weight was determined by gel permeation chromatography (GPC) and the crystallinity was tested through X-ray diffraction (XRD) .Gas permeability coefficient of N2

O2

CH4

CO2

He and H2 in these polymers at 20℃ were measured by permeate gas pressure method.The results shown that four different poly [ (tetrafluoropropoxy) 2-x (trifluoroethoxy) x ] phosphazene products with different x-value of 1.53

1.86

1.75 and 0 were prepared respectively.The glass transition temperature of these polymers were-45.2℃

-45.2℃

-50.3℃ and-32.3℃

and the weight-average molecular weight were 1.2 × 105

5.6 × 105

2.6 × 105 and 6.0 × 105 respectively.Polymer with substituted ratio x = 1.53 showed higher gas permeability.Its permeability coefficient of H2

CO2

He and O2 were 55 barrer

75 barrer

40 barrer and 15 barrer respectively.The selectivity coefficient of H2/N2 was 11.7

which showed potentiality in ammonia synthesized industry.In addition

the selectivity coefficient of O2/N2 was 3.1

demonstrated a promising oxygen-enriching material.