Crystallization and melting behavior of poly(ether ketone ketone) (PEKK) copolymers synthesized by facile one-step method

Poly(ether ketone ketone) (PEKK) is a thermoplastic with excellent performance. To date, most PEKK copolymers are synthesized by a two-step method. However, in this work, a series of PEKK copolymers with diverse T/I (terephthaloyl/isophthaloyl) ratios were firstly synthesized by a facial one-step method. Then, the structure of PEKK copolymers was characterized and the crystallization and melting behavior were studied in detail. With the increase in meta isomers in the structure, the crystallization ability and melting point of copolymers reduced, as confirmed by non-isothermal and isothermal crystallization kinetics analysis. Furthermore, the double melting behavior of PEKK copolymers after isothermal annealing was researched employing differential scanning calorimetry (DSC) and temperature-modulated DSC (TMDSC). Unlike many other outcomes, our study demonstrate that the double melting behavior is mainly related to the superimposition of rigid amorphous devitrification and enthalpy relaxation. Finally, through the self-nucleation experiment of PEKK70 and PEKK80, the ideal self-nucleation temperatures (Ts,ideal) corresponding to the copolymers were determined, then the successive self-nucleation and annealing (SSA) technology was employed to analyze PEKK copolymers for the first time, and thermal classification was successfully achieved.

Automated summary

In this study, a series of PEKK copolymers were synthesized by a one-step method and their structure and melting behavior were characterized. It was found that the increase in meta isomers in the structure led to a decrease in crystallization ability and melting point of the copolymers. The double melting behavior of the copolymers was mainly due to the superimposition of rigid amorphous devitrification and enthalpy relaxation. Additionally, the thermal classification of the copolymers was successfully achieved through self-nucleation experiment and successive self-nucleation and annealing (SSA) technology.