AZO POLYMERS FOR REVERSIBLE OPTICAL STORAGE .4. COOPERATIVE MOTION OFRIGID GROUPS IN SEMICRYSTALLINE POLYMERS

Polarized light induces a preferred orientation of azobenzene groups t hrough photochemical trans-cis-trans processes. Stronger orientation t endencies exist if the azo-containing polymers are crystalline or liqu id crystalline and the cooperative reorientation of nonactive mesogens of similar shape has been demonstrated. This paper shows that coopera tive reorientation is a more general phenomenon and can take place eve n for a nonactive rigid group of a different shape which is bonded in the main chain while the azobenzene groups are in the side chains. Com parison is made between a disperse red 1-containing amorphous azo poly mer (pDR1A) and a disperse red 19-containing semicrystalline azo polym er (pDR19T) with phenylene diacrylate (PD) groups within the main chai n. Dichroic ratios are obtained from infrared and electronic spectra a nd are correlated with a writing/erasing/rewriting sequence performed with an argon laser. A maximum birefringence of 0.08 can be obtained o n pDR1A, while on pDR19T the birefringence is 0.27 in similar conditio ns. This is the result of a combination of the semicrystallinity of pD R19T and of the cooperative orientation of PD groups along with the az obenzene groups. The drawback in terms of optical storage is the longe r time required to write or erase the induced birefringence in pDR19T.