Microstructural studies of poly(7-oxabicyclo[2.2.1]hept-2-ene) derivatives prepared from selected ruthenium catalysts

Abstract

The microstructures of polymers prepared from ring-opening metathesis polymerization (ROMP) of 7-oxanorborene (7-oxabicyclo[2.2.11 hept-2-ene) (3), endo-5-(methoxymethyl)-7-oxanorbornene (2), and exo,exo-5,6-bis(methoxymethyl)-7-oxanorbornene (1) with four metathesis catalysts were studied by ^1H and ^(13)C NMR spectroscopy. Tacticities were determined by hydrogenation of the polymers (which removed double-bond isomerism) and also by ROMP of (S)-endo-5-(methoxymethyl)-7-oxanorbornene (2S)(which related head-tail isomerism with tacticity). Polymers prepared from W(CH-t-Bu)(NAr)(OCMe(CF_3)_2)_2 (Ar = 2,6-diisopropylphenyl) (6) have all cis double bonds and are highly syndiotactic, while those from RuCl_3•3H_2O (8) and [RCl(µ-Cl)(η^3:η^3-C_(10)H_(16)]_2 (C_(10)H_(16)) = 2,7-dimethyloctadienediyl) (9) have a high trans double-bond content and are highly isotactic. Polymers prepared from [Ru(H_2O_6](tosylate)_2 (7) exhibit roughly equal amounts of cis and trans double bonds that are randomly distributed in the polymer chain and are atactic. The apparent correlation between double-bond isomerism and tacticity for a classical hexacoordinated metal center is consistent with the model proposed by Ivin and co-workers.