The low-temperature solution polycondensation technique was employed for the synthesis of novel aromatic polyamides containing both fluorene or xanthene cardo moieties and fluorinated phenoxy pendant groups as shown in Scheme 2.
We can interpret the result by the presence of the flexible fluorinated phenoxy pendant groups and bulky fluorene or xanthene cardo structures, which inhibited the close packing of the polymer chains and weakened intermolecular hydrogen bonding, thus resulting in the amorphous nature of these polyamides.
These new polyamides exhibited higher solubility than the conventional aromatic polyamides, which is attributed to the presence of fluorinated phenoxy pendant groups and bulky fluorene or xanthene cardo structures in the polymer backbone, which resulted in the decrease in the interaction of polymer chains by increasing the distance between polymer chains.
In addition, the polyamides containing xanthene cardo groups exhibited slightly lower [T.
As shown in Table 3, the design of polyamides with the incorporation of fluorinated phenoxy pendant group and bulky fluorene or xanthene cardo structure provides not only excellent solubility but also high thermal stability.
The decreased dielectric constants of these fluorinated polyamides could be attributed to the incorporation of fluorine substituents into polymers because of the small dipole and the low polarizability of the C--F bond as well as the increase in the free volume and also because of the decrease in the water absorption [46, 47], Additionally, the incorporation of bulky fluorene or xanthene cardo groups into polymer backbones can result in a less efficient chain packing and further reduce the number of polarizable groups per unit volume, thus also decreasing the dielectric constant.
Among synthetic dyes most used by the food market are erythrosine, included in the class of xanthene dyes, and brilliant blue, classified as a triphenylmethane dye (BRASIL, 2005).
The xanthene class of food dyes is widely used in coloring foods, especially Erythrosine, being behind only the Azo dye class.