Toughening of poly(propylene carbonate) by hyperbranched poly(ester-amide) via hydrogen bonding interaction

Poly(propylene carbonate) (PPC) is a biodegradable alternative copolymer of propylene oxide and carbon dioxide. As an amorphous polymer with lower glass transition temperature around 35 degrees C, PPC shows poor mechanical performance in that it becomes brittle below 20 degrees C and its dimensional stability deteriorates above 40 degrees C; thus toughening of PPC is urgently needed. Here we describe a biodegradable hyperbranched poly(ester-amide) (HBP) that is suitable for this purpose. Compared with pure PPC, the PPC/HBP blend with 2.5 wt% HBP loading showed a 51 degrees C increase in thermal decomposition temperature and a 100% increase in elongation at break, whilst the corresponding tensile strength remained as high as 45 MPa and tensile modulus showed no obvious decrease. Crazing as well as cavitation was observed in the scanning electron microscopy images of the blends, which provided good evidence for the toughening mechanism of PPC. The intermolecular hydrogen bonding interaction confirmed by Fourier transform infrared spectral analysis proved to be the reason for the toughening phenomenon. (C) 2011 Society of Chemical Industry