Macromolecules, 35 (9), 3553 -3562, 2002. 10.1021/ma012184n S0024-9297(01)02184-2
Web Release Date: March 27, 2002

Copyright © 2002 American Chemical Society

Nanotailored Crystalline Morphology in Hexagonally Perforated Layers of a Self-Assembled PS-b-PEO Diblock Copolymer

Lei Zhu, Ping Huang, William Y. Chen, Qing Ge, Roderic P. Quirk, and Stephen Z. D. Cheng*

Maurice Morton Institute and Department of Polymer Science, The University of Akron, Akron, Ohio 44325-3909

Edwin L. Thomas

Department of Materials Science and Engineering, Massachusetts Institute and Technology, Cambridge, Massachusetts 02139

Bernard Lotz

Institute Charles Sadron, 6 Rue Boussingault, Strasbourg 67083, France

Benjamin S. Hsiao, Fengji Yeh, and Lizhi Liu

Department of Chemistry, The State University of New York at Stony Brook, Stony Brook, New York 11794-3400

Received December 17, 2001

Revised Manuscript Received February 19, 2002

Abstract:

Nanoscale tailored polymer crystalline morphology is studied in a polystyrene-b-poly(ethylene oxide) (PS-b-PEO) diblock copolymer with number-average molecular weights for the PS and PEO blocks being 17 000 and 11 000 g/mol, respectively. The PEO volume fraction is 0.39. After large amplitude planar reciprocating shear, a hexagonally perforated layer (HPL) structure is obtained. Since the glass transition temperature of the PS blocks (72 C) is higher than the PEO crystal melting temperature (~51 C when the crystallization temperature, Tc, is lower than 40 C), the PEO block crystallization is confined within the HPL structure. The PEO crystal (the c axis) orientation within this complex confined environment is investigated using simultaneous synchrotron two-dimensional small-angle and wide-angle X-ray scattering (SAXS and WAXS) methods. The PEO crystal orientations with respect to the layer plane (or the {000l}) of the HPL structure have been found to be dependent upon Tc. At very low Tcs (below -50 C), the PEO crystals have a random orientation. Between -50 C Tc -10 C, the PEO crystal c axes preferentially orient parallel to the layer plane. Above Tc = 0 C, the crystal c axes orient inclined to the layer plane of the HPL structure, and the tilt angle with respect to the layer plane increases with Tc. Contrary to the confined polymer crystallization in nanolamellar structure, however, the c axis orientation perpendicular to the layer plane is not found at least up to Tc = 40 C in this HPL confined environment. Meanwhile, the ribbonlike PEO crystal growth is specifically tailored along the {100} planes of the hexagonal PS perforations. Apparent crystallite size analyses using the Scherrer equation confirm the one-dimensional crystal growth at high Tcs. Using time-resolved WAXS experiments, the crystal orientation is observed to occur in the early stage of crystallization with a crystallinity of ~7 wt %. Based on the results of specifically designed self-seeding experiment, the crystal orientation is determined by the crystal growth (surface nucleation) in the confined HPL phase rather than the preorientation of primary nuclei.

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