Bimodal Crystallization Kinetics of PBT/PTHF Segmented Block Copolymers: Impact of the Chain Rigidity
Résumé
By combining linear rheology and differential scanning calorimetry experiments performed under isothermal and nonisothermal conditions, we clarify the mechanisms of crystallization occurring in three industrially relevant PBT/PTHF segmented block copolymers. After a careful and systematic analysis of the crystallization kinetics based on "classic" Avrami-like models (1 < n < 2), we reveal (and quantify) the two-step nature of the PBT segments' association. Besides, we discuss the role of the hard (PBT) and soft (PTHF) segments' length by confronting our results to PBT homopolymers. As expected, while 2 kg mol -1 PTHF segments are found to delay substantially the crystallization of the PBT within the copolymers, we demonstrate that shortening them down to 1 kg mol -1 results in similar kinetics as for neat PBT lamellar crystallization. This result, raising fundamental questions on the chains' conformation, is finally discussed jointly with our rheological tests (gelation) and recent theoretical predictions with the aim to bring new insights into the topology of such complex systems. © Copyright 2019 American Chemical Society.