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Calculations of the Effects of Substituents on the Conformations of Pbzt and Pbo Model Compounds

Published online by Cambridge University Press:  26 February 2011

B. L. Farmer ,
Scott G. Wierschke  and
W. W. Adams
B. L. Farmer
Affiliation:
Department of Materials Science, University of Virginia, Charlottesville, VA 22901
Scott G. Wierschke
Affiliation:
Polymer Branch, Materials Laboratory, Wright-Patterson Air Force Base, OH 45433–6533
W. W. Adams
Affiliation:
Polymer Branch, Materials Laboratory, Wright-Patterson Air Force Base, OH 45433–6533
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Abstract

Semiempirical energy calculations have been used to investigate the conformational properties of poly(p-phenylene benzobisthiazole) (PBZT) and poly(p-phenylene benzobisoxazole) (PBO) having various substituents on the phenyl ring. Substituents considered included methyl, ethyl, t-butyl, hydroxyl, phenyl, and benzthiazole groups. The torsional potential for rotation about the backbone bond joining the phenylene and heterocyclic rings has a significant influence on the conformational energies. X-ray structure data and results of semiempirical molecular orbital calculations were used to determine this critical parameter.

The results show that most substituents have surprisingly little influence on the conformations of the molecules. In most cases, the substituent causes a rotation of the backbone rings away from coplanarity, but once the steric interactions are relieved, there is considerable latitude for further rotation. The substituents most effective in locking the molecules into specific conformations were hydroxyl and t-butyl, due, respectively, to the prospect for hydrogen bonding, and non-planarity. In most cases, the conformational freedom is such that packing considerations could significantly influence the conformations of the materials in the solid state.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 134: Symposium J – Materials Science and Engineering of Rigid-Rod Polymers , 1988 , 447
Copyright
Copyright © Materials Research Society 1989

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