Crystallization Within Melt-Ordered Semicrystalline Block Copolymers: Exploring the Coexistence of Microphase-Separated and Spherulitic Morphologies

Published

October 1, 2001

Author(s)

G Kim, Charles C. Han, M Libera, C L. Jackson

Abstract

The crystalline and microphase-separated morphology of semicrystalline block copolymers are compared in bulk (0.5-1 mm) and thin films (5-0 m), as characterized by transmission electron microscopy (TEM) and polarized light microscopy (PLM). Bulk films of a triblock copolymer of polystyrene, polybutadiene and polycaprolactone, (PS) _0.35 (PB) _0.15 (PCL) _0.5, where the subscripts denote the mass fraction, show a lamellar-cylindrical microphase separated morphology with a lamellar repeat of approximately 62 nm, as observed by TEM. Bulk films of a diblock copolymer consisting of (PB) _0.2 (PCL) _0.8 show an imperfect cylindrical microphase-separated structure by TEM coexisting with crystalline lamella of PCL. For both bulk specimens, the PLM shows a speckle pattern of birefringence that confirms that the PCL is crystallized within the microphase-separated structure, but no large-scale spherulites are observed by PLM. The microstructure in the as-cast thin films (5-10 m) by TEM is lamellar-cylindrical for the triblock copolymer and cylindrical for the diblock copolymer, as described above for the bulk specimens. Upon thermal treatment of these thin films, large and well-defined PCL spherulites are observed by PLM for both block copolymers. TEM of the thermally treated triblock copolymer thin films show that after the formation of spherulites, the microphase structure is no longer lamellar-cylindrical, but entirely dominated by PCL lamellar crystals. In contrast, TEM of the thermally treated diblock copolymer thin films shows that the PCL lamellar crystals coexist with the PB microphase separated cylinders after the formation of PCL spherulites. Bulk specimens could not be induced to form spherulites under similar thermal annealing conditions.

Citation

Macromolecules

Volume

34

Issue

No. 21

Pub Type

Journals

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Keywords

block copolymer, bulk films, crystalline, microscopy, morphology, semi-crystalline, TEM

Citation

Kim, G. , Han, C. , Libera, M. and Jackson, C. (2001), Crystallization Within Melt-Ordered Semicrystalline Block Copolymers: Exploring the Coexistence of Microphase-Separated and Spherulitic Morphologies, Macromolecules, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=851769 (Accessed July 27, 2024)