Polybenzoxazole membranes from self-cross-linkable aromatic polyimide membranes

A process for separating at least one gas from a mixture of gases comprising providing a polybenzoxazole membrane of formula (III) wherein said formula (III) is:

• wherein X1 is selected from the group consisting of
• and mixtures thereof;
• wherein X3 is selected from the group consisting of
• and mixtures thereof;
• wherein X4 is selected from the group consisting of
• and mixtures thereof;
• Y1 is selected from the group consisting of
• and mixtures thereof;
• Y2 is selected from the group consisting of
• and mixtures thereof, and —R′— is selected from the group consisting of
• and mixtures thereof;
• o and q are independent integers from 2 to 500:
• contacting the mixture of gases to one side of the polybenzoxazole membrane of formula (III) to cause at least one gas to permeate said membrane;
• and removing from an opposite side of said polybenzoxazole membrane of formula (III) a permeate gas composition comprising a portion of said at least one gas that permeated said membrane, wherein said polybenzoxazole membrane of formula (III) is derived from a self-cross-linkable aromatic polyimide polymer obtained from hydroxyl- and carboxylic acid-containing aromatic diamines.