Phenylacetylene thermal polymerization

The reaction mechanism of arylacetylene thermal polymerization has been studied on 4-(l-hexyloxy)-phenylacetylene i, used as a monofunctional model compound. Its linear dimers 2-5 [a diyne and 3 enyne isomers] were also synthetized and their thermal behavior investigated. Reaction products were analyzed by chromatography (HPLC, SEC), spectroscopy ( H and NMR) and spectrometry (SIMS) techniques. 

Despite the large number of available literature data, the complete understanding of this unusual radical polymerization is still not fully understood. In this paper, we report the results of our studies on the thermal polymerization of 4-(l-hexyloxy)-phenylacetylene 1 and its four linear dimers to try to answer two questions ... 

In 2010, Buchmeiser [56] developed a similar system that capitalized on the thermally reversible carboxylation [11] of NHCs (Scheme 31.13, inset). By employing the NHC-CO2 adduct (which essentially is a protected NHC), the reaction conditions did not have to be stringently air- and moisture-free to prevent NHC decomposition. Synthesis of the norbornene-functionalized monomer 37 allowed the molybdenum-catalyzed ROMP with l,4,4a,5,8,8a-hexahydro-l,4,5,8-exo-ewdo-dimethanonaphthalene (a ditopic norbornene) to produce crossHnked polymer 38 with pendant CO2-masked NHCs (Scheme 31.13). Upon heating in the presence of Rh, Ir, or Pd species, the NHC-metal-functionalized polymers 39 were formed and found to contain >20mol% metal, as determined with inductively coupled plasma optical emission spectrometry (ICP-OES). The C02-masked NHC material was found to catalyze the carboxylation of carbonyl compounds and the trimerization of isocyanates upon thermal deprotection (i.e., decarboxylation). Moreover, the NHC-metal-crosslinked materials were found to catalyze Heck reactions, transfer hydrogenations, and also the polymerization of phenylacetylene (M = 8.4 kDa, PDI = 2.45, as determined with GPC in DMF against PS standards). This modular system provides an array of options for catalysis from simple modifications of polymer-supported, C02-masked NHCs. 

---