Thermal cis–trans isomerization of 4-diethylamino-4′-methoxyazobenzene in poly(D(−)3-hydroxybutyrate) and its hydroxyvalerate copolymer as a probe for characterizing their aging

The aging of bacterial polyester poly(D (—)3-hydroxybutyrate) has been studied by coloring it with 4-diethylamino-4′-methoxyazobenzene and determining the reduction in isomerization rate of the dye with aging, such a reduction being a measure of the loss in polymer sequential mobility that is responsible for the considered phenomenon. A preliminary test carried out on poly(ethylene terephthalate) colored with 4-diethylaminoazobenzene proved the isomerization of the dispersed dye to be a sound probe for determining the aging process. In the case of the bacterial polyester, the aging process appeared even above the polymer T_g value measured by calorimetric analysis. The kinetics and rate coefficients of aging were determined at 30°C for the examined polymers. Aging in the copolymer poly(hydroxybutyrate-hydroxyvalerate) was also investigated. © 1995 John Wiley & Sons, Inc.