THERMAL-ISOMERIZATION OF AZOBENZENE-BASED ACRYLIC-MONOMERS AND (CO)POLYMERS WITH DIMETHYLAMINO SUBSTITUENTS IN SOLUTION - INFLUENCE OF ADDITION OF (POLY)ACID, COPOLYMER COMPOSITION, SPACER LENGTH, AND SOLVENT TYPE

This study reports on a method for influencing the thermal isomerizati on of azobenzene-based acrylic monomers and (co)polymers by means of i nteraction between basic polymeric and monomeric azobenzenes (modified with a basic dimethylamino substituent, (polyazobases) and (poly)acid s. The results indicate that acid catalysis is the predominant effect, which is controlled by (inter)polymer cooperative hydrogen bonding, b ecause on addition of the low molecular weight isobutyric acid (IBA) t o the (polyazobases no effect was observed, and on addition of poly(me thacrylic acid) (PMA) to the monomeric azobases only a weak effect was found. On addition of PMA, the rate constant of the thermal cis to tr ans isomerization (k(T-isom)) of a polyazobase could be enhanced by a factor of 70. The influences of factors like copolymer composition, sp acer length, solvent type, and stabilization time after mixing on the thermal isomerization were also investigated and explained in terms of polymer complexation. In the absence of PMA the rate of the thermal i somerization was found to decrease by introduction of a spacer, by low ering the azobase monomer content in copolymers and by improving the s olvent quality. The results on the thermal cis to trans isomerization presented here were obtained from measurements in dilute solution with concentrations well below c, because in that case polymer matrix eff ects could be ruled out.