Second order nonlinear optical polyimides having benzobisthiazole-based pendant groups, and preparation of the same

A process for preparing a second order nonlinear optic polyimide polymer of formula (I),

• wherein:
• R1 is a functionality group selected from —OH and —COOH;
• R2 is a group represented by the formula selected from
• wherein when R1 is —OH, R2 is a group represented by the formula:
• and
• when R1 is —COOH, R2 is a group represented by the formula:
• wherein R is a phenyl or styryl group that is 3-substituted with a group selected from the —NO2, —COCH3, —CN, —SO2NH2, Br and Cl;
• and
• x+y+z=100% of the repeating units, x is at least 1%, and either or both of y and z can be zero;
• the process comprising the steps of:
• reacting 4,4′-(hexafluoroisopropylidene)diphthalic anhydride with a compound of formula
• wherein R1 is the same as that defined for formula (I), optionally in the presence of m-phenylenediamine, so as to form a host polyimide polymer comprising repeating units represented by the formula:
• wherein R1, x, y and z are the same as those defined for formula (I);
• and
• grafting the thus formed host polyimide polymer with a compound of formula R2″—H so as to form an intermediate polyimide polymer comprising repeating units represented by the formula (I′), which is processible to form the second order nonlinear optic polyimide polymer of formula (I):
• wherein:
• R1, x, y and z are the same as those defined for formula (I);
• when R1 is —OH, R2″ and R2′ are the same and represent a group of formula
• when R1 is —COOH, R2″ represents a group of formula
• and R2′ represents a group of formula
• wherein R is a phenyl or styryl group that is 3-substituted with a group selected from —NO2, —COCH3, —CN, —SO2NH2, Br and Cl.