ELSEVIER Synthetic Metals 74 (1995) 99-102 SWTiiETII[ IMITIS Poly(cyclopentadienylene vinylene)s: synthesis via ROMP, chemical and physical properties Michael Schimetta ", G(inther Leising b, Franz Stelzer a a Christian Doppler Laboratoriumfiir Katalytische Polymerisation, Institutfiir Chemische Technologie Organischer Stoffe, Technische Universitdt Graz, Stremayrgasse 16, A-8010 Graz, Austria b lnstitutfiir FestkOrperphysik, Technische Universitiit Graz, Petersgasse 16/11, A-8010 Graz, Austria Received 7 December 1994; revised 10 June 1995; accepted 12 June 1995 Abstract Norbornene derivatives, bearing different substituents, were polymerized via ring-opening metathesis polymerization (ROMP). This paper mainly reports on possibilities of controlling the stereochemistry of the polymerization reaction to give stereoregular precursors to conjugated polymers. The precursor polymers were then converted to the corresponding conjugated polymers through thermal or base-induced elimination. Monomers used for the polymerization were norbornenebis(methylcarbonate), norbomenebis(S-methyldithiocarbonate) and benzonorbor- nadienes substituted with isopropylidene, methylbenzylidene, phenylbenzylidene andp-fluorophenyl-p-fluorobenzylidene groups at the bridge carbon. Resulting polymers were then converted to poly(cyclopentadienylene vinylene) or more rigid highly substituted poly(cyclopentadienylene vinylene)-bearing exocyclic double bonds. Characterization was carded out by spectroscopic methods on thin films (photoluminescence, IR, UV-Vis-NIR, ~H and ~3CNMR spectroscopy). Keywords: Poly (cyclopentadienylene vinylene)s; Synthesis; Metathesis polymerization 1. Introduction Use of precursor polymers is one common way to conju- gated polymers. Polyacetylene via a precursor polymer was first achieved by an elegant route established by Feast and co-workers [ 1-3] that showed some useful features [4]. A way to poly(p-phenylene) (PPP) via thermal acid extrusion of acetates was first shown by ICI workers [5,6]. The major disadvantages of this route were the price and commercial availability of the monomer and the limited control over ster- eochemistry. Similar routes were applied for the synthesis of poly(phenylene vinylene) [7] and poly(cyclopenta- dienylene vinylene) [8,9]. Theoretical studies on conjugated polymers [ 10,11 ] showed a dependence of the bandgap on the conformation of the conjugated polymer. Therefore, it was interesting to syn- thesize precursor polymers with high tacticity and well- defined stereoregularity. Ring-opening metathesis polymerization (ROMP) of norbornene derivatives bearing sterically demanding substituents proved to be a way to these well-defined precursor polymers. Variation of substituents (as shown below) from acetate to dixanthate in positions 2 and 3 of norbornenediol or from methyl- to p-fluorophenyl benzylidenebenzonorbornadienes allowed the control of the 0379-6779/95/$09.50 © 1995 Elsevier Science S.A. All rights reserved SSD10379-6779 (95)03366-R stereochemistry of the polymerization and the electrical and optical properties of the conjugated polymer. R2 la-d 2a-d R1, P~ = a) methyl, methyl F~ = a) acetate, b) benzoate, b) methyl, phenyl, e) carbonate, d) xanthate e) phenyl, phenyl d) pfluorophenyl,p-fluorophenyl Thermal elimination of esters as a precursor route to con- jugated polymers usually was applied to esters like acetates or benzoates. Precursor polymers with these functional groups [9] usually showed glass transitions between 50 and 100 °C and decomposed at temperatures above 300 °C. At these temperatures, uncontrolled side reactions (crosslink- ing, oxidation, degradation, etc.) occurred that did not allow formation of high conjugation lengths. So it was attempted to reduce the temperature of elimination into the region of the glass transition by substitution with S-methyldithiocar- bonate ( = dixanthate) groups. The literature indicated little