Synthesis and Properties of a Variety of Well-Defined Hyperbranched <i>N</i>-Alkyl and <i>N</i>-H Polyamides by Chain-Growth Condensation Polymerization of AB<sub>2</sub> Monomers

Well-defined hyperbranched polyamides (HBPAs) were synthesized by means of chain-growth condensation polymerization of AB<sub>2</sub> monomers from core molecules, making use of the change of substituent effects between the monomer and the polymer. Polymerization of 5-(methylamino)isophthalic acid ethyl ester <b>1c</b> as an AB<sub>2</sub> monomer with core <b>3b</b> was carried out in the presence of lithium 1,1,1,3,3,3-hexamethyldisilazide (LiHMDS) and LiCl in THF at −30 °C to yield HBPA with low polydispersity (<i>M</i><sub>w</sub>/<i>M</i><sub>n</sub> ≤ 1.13) and well-defined molecular weight (<i>M</i><sub>n</sub> = 2370–39300) depending on the feed ratio of the monomer to the core (from 7 to 200). The matrix-assisted laser desorption ionization time-of-flight (MALDI–TOF) mass spectra showed that the obtained HBPA included the core unit, indicating that the polymerization proceeds by selective reaction of the monomer with the core and the polymer ends, without side reactions. Polymerization of other AB<sub>2</sub> monomers with <i>N</i>-ethyl, octyl, and 4-octyloxybenzyl (OOB) groups afforded the corresponding well-defined HBPAs. HBPA with the <i>N</i>-OOB group was converted to unsubstituted <i>N</i>-H HBPA with low polydispersity by treatment with trifluoroacetic acid (TFA). The solubility of HBPAs depended upon the nature of the <i>N</i>-alkyl groups and the terminal ester moieties. The glass transition temperature (<i>T</i><sub>g</sub>) and 10% weight-loss temperature (<i>T</i><sub>d</sub><sup>10</sup>) of HBPAs depended upon the molecular weight, as well as the nature of the <i>N</i>-alkyl groups and terminal ester moieties.