Synthesis, characterization, and properties of PCDL aliphatic hyperbranched polyurethane coatings

The isocyanate-terminated polyurethane pre-polymer (PPU) was synthesized via the step-growth polymerization approach by using polycarbonate diol (PCDL, Mn = 2000) and isophorone disocyanate (IPDI) as monomers, dibutyltin dilaurate (DBTDL) as the catalyst. Subsequently, the hyperbranched polyurethane (HBPU) was synthesized by graft copolymerization using PPU, hyperbranched poly(amide-ester) polyol (HPAE) and 1,4-butanediol (BDO). The molecular structure of HBPU was characterized by means of FTIR, H-1-NMR, and C-13-NMR. It was observed that HBPU was synthesized as anticipated. The thermal and mechanical properties, the microstructure, and morphologies of the filmed HBPU and LPU (linear polyurethane) were tested, respectively. The filmed HBPU, revealed better thermal stability, and higher T-g accompanied with lower viscosity than those of filmed LPU. Additionally, the mechanical experiment showed that the filmed HBPU exhibited enhanced mechanical properties because it contained certain amounts of HPAE. Compared with its linear analog (LPU) specimen, the tensile strength of the filmed HBPU containing 10 wt % HPAE increased by 1.9 times (up to 28.15 MPa), and its elongation at break increased by 1.5 times (up to 543.8%), resulting from the dual effects of the hydrogen bonding and the crosslinking density in the HBPU system. The morphologies of filmed HBPU were characterized by means of WAXD and SEM, which indicated that increasing the content of HPAE lowers the crystallinity of HBPU. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2671-2679, 2013