Synthesis and photochemical reactions of main-chain polymers containing cinnamoyl groups

Poly(amide-imide)s containing 4-carboxycinnamic acid as a photoreactive building block were prepared by direct polycondensation at 160 degrees C of 1,6-diisocyanatohexane (HMDI), trimellitic anhydride and 4-carboxycinnamic acid (PCCA) in N-methyl-pyrrolidone (NMP) in the presence of organic bases as catalyst. Transparent and flexible films could be cast onto quartz plates from polymer solutions. Upon irradiation of the polymers in solution and in solid state (films), the cinnamoyl chromophores undergo (2 + 2) photocycloaddition. Decrease in cinnamoyl moieties based on photodimerization between cinnamoyl moieties during the UV irradiation was evaluated from the change in absorption spectra.