Synthesis and structural characterization of poly(dicyclopentadiene) gels obtained with a novel ditungsten versus conventional W and Ru mononuclear catalysts

Abstract

Poly(dicyclopentadiene) (PDCPD) gels were prepared via ring opening metathesis polymerization (ROMP) of dicyclopentadiene (DCPD), which is known to provide highly crosslinked insoluble polymers. Two catalytic systems were employed, both based on W compounds. The first one was based on the ditungsten complex Na[W2(μ-Cl)3Cl4(THF)2]·(THF)3 ({W3W}6+, a′2e′4) and the second one on commercially available WCl6. Both catalysts require activation by small amounts of phenylacetylene (PA). Dry-gels were characterized with TGA, FTIR-ATR, FT-Raman and solid-state NMR, and were compared with PDCPD aerogels synthesized using the well-established first and second generation Ru-based Grubbs’ catalysts (Ru-I and Ru-II). Emphasis is given on the determination of the cis/trans ratio of the polymeric chain. Data confirmed that Ru-based catalysts favor the trans-configuration, while W-based catalysts favor the cis-configuration, in accord with the stereoselectivity that has been observed with those catalytic systems in other ROMP reactions of substrates that yield soluble polymers. Most importantly, it is also shown that the configuration of the polymeric chain plays a key role in the swelling behavior of those PDCPD dry-gels in toluene. High-cisPDCPD gels obtained from the ditungsten catalytic system increased their volume by more than 100 times, while gels obtained with the other catalytic systems swelled to a much lesser extent (WCl6/PA, Ru-II), or did not swell at all (Ru-I). It is evident that swelling strongly depends on the configuration of the polymeric chain and increases together with the content of the cis configuration. Therefore, the ditungsten catalytic system shows unique advantages in terms of stereochemistry and properties of PDCPD gels over the mononuclear W- and Ru-based catalytic systems.