Linear-hyperbranched copolymerization as a tool to modulate thermal properties and crystallinity of a para-poly(ether-ketone)

The AB₂ monomer, 3,5-bis(4-fluorobenzoyl)phenol was synthesized via an improved four-step scheme. It was polymerized to form the corresponding fluoride-terminated hyperbranched polymer with higher molecular weight than previously reported, as evidenced by higher glass-transition temperature (T_g=159 °C vs. 140-143 °C). The homopolymerization showed a bimodal molecular weight distribution that was also observed for other related linear-hyperbranched systems. The AB₂ monomer was then copolymerized with 4-fluoro-4′-hydroxybenzophenone (AB monomer), in weight ratios of 1:3, 1:1 and 3:1 to afford the respective hyperbranched poly(ether-ketones) with variable degrees of branching. The 1:1 copolymer had T_g value (212 °C) that was significantly (35 °C) higher than both linear and hyperbranched homopolymers. Only the 1:3 copolymer was semi-crystalline, displaying melting at 340 °C and its wide angle X-ray scattering (WAXS) pattern indicated that its crystal structure is exactly the same as that of the linear homopolymer. The WAXS results of the copolymers correlated well with differential scanning calorimetry and themogravimetric analysis results.