Swelling of semi-crystalline PVDF by a PMMA-based nanostructured diblock copolymer: Morphology and mechanical properties

The influence of a self-organizing diblock copolymer on the morphology, crystallinity and mechanical properties of a high molecular weight polyvinylidene fluoride (PVDF) is investigated. A spherically organized nanostructured diblock copolymer containing 25 wt% of soft acrylate block and 75 wt% of rigid polymethylmethacrylate (PMMA) is incorporated in PVDF in proportions varying between 12.5 and 70 wt% copolymer. DSC and DMA experiments prove the miscibility of the glassy PMMA block with the amorphous fraction of PVDF, whereas the soft block is fully segregated, preserving the nanostructuration of the diblock copolymer in the blend. Transmission electron microscopy and SAXS experiments show that the copolymer is confined into the inter-lamellar gallery of PVDF, giving rise to a swelling of the crystalline/amorphous lamellar morphology. The long period Lp varies from 120 A in pure PVDF to 200 A in the presence of 25 wt% copolymer. WAXS experiments and ATR spectroscopy show that the polar β polymorph is favored in the blends and that the PVDF crystallinity is preserved. Tensile tests demonstrate a large improvement of the elongation at break, without significant loss of strength for samples containing lower amounts of copolymer.