Azo polymers for reversible optical storage: 12. Poly{1-acryloyl-4-[4-(4-nitrophenylazo)phenyl] piperazine}

Two azo-containing vinyl monomers, 1-acryloyl-4-[4-(4-nitrophenylazo)phenyl]piperazine (ANPP) and 1-methacryloyl-4-[4-(4-nitrophenylazo)phenyl]piperazine (MNPP), were synthesized. MNPP did not polymerize in a few solvents, with a few free radical initiators and at a few temperatures. pANPP is amorphous with a T_g of 156 °C and decomposes above 230 °C. Birefringence can be induced by a polarized laser (514 nm) on a pANPP film to a level of 0.1 and is very stable. Comparison is made with poly{4′-[(2-(acryloyloxy)ethyl)ethylamino]-4-nitroazobenzene} (pDRIA). Biexponential curve fitting shows a lower writing rate for pANPP. Both the slow response to the laser and the higher stability of the photoinduced birefringence are due to the ‘rigid’ piperazine linkage between azobenzene groups and backbone which prevents the azo groups from rotating freely. pANPP decomposes under long term exposure to the laser.