Crystallization and multi-crystalline morphology in PE-b-PEO-b-PCL-b-PLLA tetrablock quarterpolymers and their respective precursors

Semi-crystalline block copolymers are fascinating materials. The level of complexity in their crystallization behavior increases with the number of potentially crystallizable blocks in the material. Even though a large body of literature exists on double crystalline diblock copolymers, much less has been published in the cases of triple crystalline triblock terpolymers or tetra crystalline tetrablock quarterpolymers. The morphology and crystallization of novel tetrablock quarterpolymers of polyethylene (PE), poly (ethylene oxide) (PEO), poly (ε-caprolactone) (PCL), and poly (L-lactide) (PLLA) with four potentially crystallizable blocks have been investigated. Their corresponding precursors: triblock terpolymers PE-b-PEO-b-PCL, diblock copolymers PE-b-PEO, and PE homopolymers, were also studied. The direct comparison of the results obtained with DSC, SAXS/WAXS, and polarized light optical microscopy intensity measurements allows to precisely identify the complex crystallization sequence of the blocks upon cooling from the melt. Additionally, it is demonstrated how the self-assembly during sequential crystallization can produce, depending on crystallization conditions, remarkable double, triple, and even tetracrystalline superstructures (i.e., axialites and spherulites).

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