Composite polyamide membrane having high acid content and low azo content

1. A thin film composite polyamide membrane comprising a porous support and a thin film polyamide layer characterized by possessing:

i) an azo (—N═N—) content of from 0.30% to 0.80 wt %, as measured by pyrolysis gas chromatography using ammonium dichromate as a calibration standard and pyrolizing the polyamide layer at 550° C. for 6 seconds;

ii) a dissociated carboxylate content of at least 0.20 mol/kg of polyamide as measured by RBS at pH 9.5; and

iii) an amino phenol/m-phenylene diamine ratio of at least 0.15.

2. The membrane of claim 1 wherein the thin film polyamide layer is further characterized by possessing an azo content of from 0.40% to 0.75 wt %.

3. The membrane of claim 1 wherein the thin film polyamide layer is further characterized by possessing a COOH/amide ratio of equal to or greater than 0.14, as measured by ATR IR.

4. The membrane of claim 1 wherein the thin film polyamide layer is further characterized by possessing a COOH/amide ratio of equal to or greater than 0.15, as measured by ATR IR.

5. The membrane of claim 1 wherein the thin film polyamide layer is further characterized by possessing a COOH/amide ratio of equal to or greater than 0.16, as measured by ATR IR.

6. The membrane of claim 1 wherein the thin film polyamide layer is further characterized by possessing an amino phenol/m-phenylene diamine ratio of at least 0.18.

7. The membrane of claim 1 wherein the thin film polyamide layer is further characterized by possessing:

i) an azo content of from 0.40% to 0.75 wt %;

ii) a dissociated carboxylate content of at least than 0.30 mol/kg of polyamide;

iii) a COOH/amide ratio of equal to or greater than 0.14; and

iv) amino phenol/m-phenylene diamine ratio of at least 0.18.