Morphology of a phase‐separated and a molecular composite PBT/ABPBI polymer blend

Stephen Krause, Tim Haddock, Gary E. Price, P. Galen Lenhert, Joseph F. O'brien, Thaddeus E. Helminiak, W. Wade Adams

Research output: Contribution to journalArticlepeer-review

53 Scopus citations


The structure and morphology of homopolymers and blends of rigid‐rod poly(p‐phenylene benzobisthiazole) (PBT) and semiflexible coil poly[2,5(6)benzimidazole] (ABPBI) were examined by wide‐angle x‐ray diffraction and scanning and transmission electron microscopy. When samples were processed from a solution where the total polymer concentration of 30% PBT/70% ABPBI blend was greater than a critical concentration, large‐scale phase separation occurred and 0.1–4 μm ellipsoidal particles were present in a ductile matrix. The ellipsoids were chiefly composed of aggregates of well‐oriented 10‐nm PBT crystallites, while the matrix material was chiefly ABPBI. When the concentration was less than a critical concentration, the solution was optically homogeneous. In processing of fiber and film samples from the homogeneous solution, large‐scale phase separation was inhibited by rapid coagulation in a water bath. After heat treatment, these samples were found to contain crystallites of both PBT and ABPBI with lateral dimensions of ordered regions no larger than 3 nm. The PBT homopolymer was dispersed in the matrix at the molecular level in ordered regions at a scale no larger than 3 nm, resulting in a rigid‐rod molecular composite. In the rigid‐rod molecular composite fiber both the molecular‐level dispersion and high orientation contributed to higher values of strength and modulus compared to the properties of a phase‐separated fiber. The strength and modulus of highly oriented fiber were only 25% higher than those of planar isotropically oriented film, suggesting that the level of dispersion of rod molecules is more important than orientation of the reinforcing phase in rigid‐rod molecular composites.

Original languageEnglish (US)
Pages (from-to)1991-2016
Number of pages26
JournalJournal of Polymer Science Part B: Polymer Physics
Issue number9
StatePublished - Sep 1986

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Physical and Theoretical Chemistry
  • Polymers and Plastics
  • Materials Chemistry


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