Templating and tuning the crystallization of melt miscible double crystalline diblock copolymers and triple crystalline triblock terpolymers

Triple crystalline triblock terpolymers are materials with remarkable semi-crystalline superstructures. We have studied for the first time the alternating triple lamellar morphology formed by self-assembly inside spherulites of a triblock terpolymer composed of poly (ethylene oxide) (PEO), poly (ε-caprolactone) (PCL) and poly (L-lactide) (PLLA). The morphology of the PEO-b-PCL-b-PLLA triblock terpolymer is compared to an analogous PCL-b-PLLA diblock copolymer. Both diblock and triblock form a single phase in the melt. Two crystallization protocols were employed to create particular crystalline morphologies. In both cases, the isothermal crystallization of the PLA block is induced first (at 81 ºC, a temperature above the melting points of both PCL and PEO blocks) and PLLA spherulites form a template, where upon cooling the other two blocks can crystallize within the PLLA interlamellar spaces. WAXS analysis demonstrated the double crystalline and triple crystalline nature of the materials. The lamellar structure was evaluated by AFM observations and SAXS measurements. Moreover, theoretical SAXS curves of one-dimensional structural models were calculated. AFM micrographs of the triblock terpolymer evidenced the three different lamellae of PLLA, PCL and PEO that coexist together within the same spherulite. Three different lamellar thickness were determined and their dimensions suggested that all blocks crystallized in chain-folded conformations. The evolution of the triple lamellar morphology during heating of tri-crystalline samples was followed by in-situ synchrotron SAXS measurements. The theoretical analysis of the SAXS curves of the triblock terpolymer allowed us to propose a stacking morphological model, in which a particular tri-layer structure exists, where one lamella of PCL or one lamella of PEO is inserted randomly between two adjacent PLLA lamellae. The isothermal crystallization kinetics of these terpolymers was evaluated by differential scanning calorimetry (DSC) and compared to analogous PCL-b-PLLA diblock copolymers and to PLLA, PCL and PEO homopolymers. The results are complemented by in-situ SAXS/WAXS synchrotron experiments. One, two and three step crystallization protocols were employed to study the crystallization kinetics of the blocks. Complex competitive effects such as plasticization, nucleation, anti-plasticization and confinement occurred during the isothermal crystallization of tricrystalline PEO-b-PCL-b-PLLA triblock terpolymers. 

Viernes, Mayo 18, 2018 - 12:00
Alejandro J. Müller
POLYMAT and Polymer Science and Technology Department, Faculty of Chemistry, University of the Basque Country UPV/EHU
Sala de Seminarios (Antigua Biblioteca)