Poly(ethylene oxide-b-isoprene) diblock copolymer phase diagram

G. Floudas*, B. Vazaiou, F. Schipper, R. Ulrich, U. Wiesner, H. Iatrou, Nikolaos Hadjichristidis

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

131 Scopus citations

Abstract

The phase state of 25 poly(ethylene oxide-b-isoprene) (PEO-PI) diblock copolymers spanning the composition range 0.05 < fPEO < 0.8 has been studied using small-angle X-ray scattering and theology. In addition, the thermal and thermodynamic properties have been obtained from differential scanning calorimetry and pressure-volume-temperature measurements. Twenty of the diblocks exhibit at least one order-to-order transition, and two show four ordered phases. The phase diagram consists of four equilibrium phases in the melt; lamellar (Lam), hexagonally packed cylinders (Hex), spheres packed in a body centered cubic lattice (bcc) and a bicontinuous cubic phase with the Ia3̄d space group symmetry known as the gyroid phase. The latter is formed for the range of compositions 0.4 < fPEO < 0.45 which are the highest ever reported for a stable gyroid phase. The high asymmetry in the present phase diagram is attributed to the high conformational asymmetry of the PEO and PI (ε = 2.72). At low temperatures, upon PEO crystallization, all phases revert to the crystalline lamellar structure (Lc). Within the composition range 0.66 < fPEO < 0.7 another intermediate phase is formed known as perforated layers (PL) which is clearly not an equilibrium phase. The thermal expansion coefficient was found to be a sensitive probe of the ordered microstructures.

Original languageEnglish (US)
Pages (from-to)2947-2957
Number of pages11
JournalMacromolecules
Volume34
Issue number9
DOIs
StatePublished - Apr 24 2001

ASJC Scopus subject areas

  • Materials Chemistry

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