Synthesis and Comprehensive Characterization of Bio-Based Heat-Resistant Poly(pentamethylene/dodecamethylene tere...

In this study, bio-based poly(pentamethylene terephthalamide) (PA5T), poly(pentamethy lene/dodecamethylene terephthalamide) (PA5T/12T), and poly(dodecamethylene terephthalamide) (PA12T) were synthesized using 1,5-pentanediamine, 1,12-dodecanediamine and terephthalic acid as polymerization monomers. PA12T segments with longer methylene sequences were incorporated to address the processing challenge of PA5T, whose melting temperature is close to its thermal decomposition temperature. The effects of PA12T segment content on the chemical structure, thermal properties, crystallization behavior and solvent resistance of the copolymers were investigated. Meanwhile, the thermal degradation mechanism was elucidated by thermal degradation kinetics analysis. The results show that PA5T is dominated by the γ-form, whereas PA5T/12T and PA12T exhibit the coexistence of both α- and γ-forms. With increasing content of the PA12T segment, the melting temperature and melting enthalpy of PA5T/12T decrease initially and then increase gradually, which is attributed to the combined effects of longer PA12T segments on the molecular chain architecture and crystallization behavior of the copolymers. PA5T/12T-6:4 and PA12T exhibit melting temperatures of 293.1 °C and 285.6 °C, respectively (both ≥280 °C), which meet the service-temperature requirements for heat-resistant polyamides. Meanwhile, they possess excellent solvent resistance and a wide processing window, showing considerable application potential. The thermal degradation mechanism of both PA5T/12T-6:4 and PA12T follows the R2 model, i.e., the phase-boundary-controlled reaction mechanism (contracting area). The findings provide new strategies for developing bio-based heat-resistant polyamides and deepen our understanding of the thermal degradation mechanisms of this class of polymers.