Linear polyisophthalamides from the trifunctional monomer 5-hydroxyisophthalic acid. A convenient approach towards functionalized aromatic polymers

Wholly aromatic polyisophthalamides (PIPAs) containing free hydroxylic groups were prepared from 5-hydroxyisophthalic acid and sulfonyldianiline by the condensation phosphorylation method, using triphenylphosphite as a condensing agent, in the presence of pyridine. Linear polymers were attained in high yield and high molecular weight, and the properties of the polymers were investigated in comparison with homologous polyisophthalamides without single bondOH groups. The presence of single bondOH groups did not much modified the solubility of hydroxyl-containing polyisophthalamides as they behaved against common solvents in a similar manner as that of reference polyisophthalamides. However, hydroxyl side groups greatly enhanced the water affinity of polyisophthalamides, which showed up to 16% water uptake in 98% relative humidity, and contact angles about 10° smaller than those of classical PIPAs. The presence of free single bondOH groups slightly diminished the thermal resistance, as evaluated by TGA, but the glass transition temperatures were higher by 20–30 °C, with a maximum of 345 °C. The mechanical properties of hydroxyl-containing polyisophthalamides were reasonably acceptable, with modulus around 2000 MPa and tensile strength up to 60 MPa.