Improving the heat‐resistance and toughness performance of phenolic resins by adding a rigid aromatic hyperbranched polyester

An aromatic hyperbranched polyester (AHBP) was synthesized by melt polycondensation from diphenolic acid and characterized by Fourier transform infrared spectrum (FTIR) spectra. The degree of branching (DB) value of AHBP calculated from the ¹³C‐NMR spectroscopy was 0.67. The number‐average molecular weight (M_n) and weight‐average molecular weight (M_w) of AHBP were 1792 and 4480 g/mol, respectively. Novel phenolic resins modified with AHBP (PR/AHBP) were then prepared, in which AHBP was used as toughener of phenolic resins. The effect of AHBP on the thermal properties of phenolic resins was studied by means of differential scanning calorimetry (DSC), thermal gravimetric analyses (TGA), and heat deformation temperature tests. The modified resins presented higher glass transition temperature (T_g) than the unmodified system due to that the rigid backbone structure of AHBP with a great deal of the benzene ring groups restricted the mobility of the chain segments of macromolecules. The DSC, scanning electron microscopy (SEM) analyses showed that AHBP had good compatibility with phenolic resin, and the modified resins showed ductile fracture. The results of mechanical performance measurements exhibited that the impact strength of PR/AHBP containing 15 wt % AHBP was about 130% higher than that of the neat phenolic resin, suggesting that the toughness of PR/AHBP was significantly improved by the addition of AHBP. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42734.