Effects of polycaprolactone molecular weights on thermal and mechanical properties of polybenzoxazine

Polymer blends of polybenzoxazine (PBA-a) and polycaprolactone (PCL) of different molecular weights (M-n=10,000, 45,000, and 80,000 Da) were prepared at various PBA-a/PCL mass ratios and their properties were characterized. The results from dynamic mechanical analyzer (DMA) revealed two glass transition temperatures implying phase separation of the two polymers in the studied range of the PCL contents. Moreover, a synergistic behavior in glass transition temperature (T-g) was evidently observed in these blends with a maximum T-g value of 281 degrees C compared with the T-g value of 169 degrees C of the PBA-a and about -50 degrees C of the PCL used. The blends with higher M-n of PCL tended to provide greater T-g value than those with lower M-n of PCL. The modulus and hardness values of PBA-a were decreased while the elongation at break and area under the stress-strain curve were increased with an increase of the content and M-n of PCL, suggesting an enhancement of toughness of the PBA-a. Scanning electron micrographs (SEM) of the sample fracture surface are also used to confirm the improvement in toughness of the blends. (c) 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41915.