The Synthesis, Characterisation and Electro-Optical Properties of Polypentenylene-Block-Co-Acetylene

Abstract

Acetylene was polymerised using the metathesis catalysts WCl6/LiBu, WCI6/AIEtCl2and WCI6/AIEt3. The polyacetylene was characterised by infra-red spectroscopy, elemental analysis and scanning electron microscopy. Block copolymers containing polyacetylene and polypentenylene segments were synthesised by sequential addition of cyclopentene and acetylene to an active metathesis catalyst system. When WCI6/AIEtCl2 was used as catalyst, the copolymer was a black elastomeric material that was soluble in a range of organic solvents and dissolved to give intensely coloured solutions even at low concentration. Soluble copolymers were characterised by uv/visible spectroscopy, infra-red spectroscopy and gel permeation chromatography. The results of these studies indicated that the catalytic species that polymerises cyclopentene is not identical to the one that is responsible for the polymerisation of acetylene. It seemed likely that the polymerisation of acetylene using metathesis catalysts proceeded by a Ziegler/Natta co-ordinated anionic type mechanism. An improved synthetic route to polypentenylene-block-co-acetylene employed a reaction scheme that involved an active site transformation reaction. The synthetic conditions were manipulated to effect control over block length of the polyene blocks. The length of the blocks of polypentenylene were reduced by the incorporation of a linear alkene during the ring opening metathesis polymerisation step of the synthesis. A simple electro-optical technique was developed for the simultaneous measurement of electrically induced birefringence and electrically induced dichroism. This technique was used to determine the electric birefringence and dichroism of solutions of polypentenylene-block-co-acetylene in cyclohexane. The results indicated that the copolymer exists as a polydisperse distribution of optically anisotropic aggregates in solution. The most plausible model of the electro-optical behaviour is one in which the polyacetylene segments of the copolymer form a rod-like core that is surrounded by as hell comprising chains of polypentenylene.