New polymer syntheses, 91 . Hyperbranched poly(ester‐amide)s derived from 3,5‐dihydroxybenzoic acid and 3,5‐diaminobenzoic acid

A new pentafunctional monomer ( 3a ) was prepared by acylation of silylated 3,5‐diaminobenzoic acid (DABA) with 3,5‐bisacetoxybenzoyl chloride. The polycondensation of this monomer or its trimethylsilyl ester yielded a hyperbranched poly(ester‐amide) having a nearly alternating sequence of one DABA and two 3,5‐dihydroxybenzoic acid (DHBA) units. However, due to ester‐amide interchange reactions, ca. 15–25% of the DABA units lose their role as branching units. When 3,5‐bisacetoxybenzoic acid and 3,5‐bisacetamidobenzoic acid were copolycondensed in a 2:1 ratio, the resulting polymer and endgroup structures were different. Furthermore, hyperbranched copoly(ester‐amide)s with a variable DHBA/DABA ratio from 10:0 down to 3:7 were prepared. The glass transition temperature ( T g ) increased by approx. 90°C (up to 250°C) at higher molar fractions of DABA. Furthermore, monomer 3a was copolycondensed with 3‐acetoxybenzoic acid or its trimethylsilyl ester. The resulting copoly(ester‐amide)s were again amorphous, showing a continuous decrease of the T g down to the value of the poly(3‐hydroxybenzoic acid) (poly(3‐HBA)) around 136–140°C.