Synthesis and properties of polyurethane elastomers crosslinked with amine-terminated AB2-type hyperbranched polyamides

Amine-terminated AB2-type hyperbranched polyamides of different molecular weights were prepared from 3,5-bis-(4-aminophenoxy)benzoic acid (AB2 monomer) by fractional precipitation technique and characterized by FTIR, 1H-NMR spectroscopies, DSC and GPC techniques. The degree of branching (DB) of hyperbranched polymers (HBP) was determined using 13C-NMR spectroscopy and it was found that the value increased with decrease in molecular weight of polymer considered. As the molecular weight distribution was narrow, the approximate number of end functional groups of each HBP was conveniently calculated. Three polymers were selected and used as crosslinkers in the preparation of polyurethanes. The incorporation of hyperbranched polyamide into the polyurethane chains was confirmed using FTIR and 1H-NMR spectroscopic techniques. Among the range studied (1–6%), it was found that high tensile strength is attained with 1% of HBP. It was also found that the tensile strength decreases with increase in number of end functional groups and decrease in DB of HBP. However, glass transition temperatures and thermal stability of polyurethanes crosslinked with up to 6% of HBP, above which gelation occurred, were not affected and similar to the blank polymer prepared without AB2 polymer.