Unusually facil cis to trans isomerization of a polypropiolate bearing a long alkyl chain polymerized using a [Rh(norbornadiene)Cl]2 catalyst: An ESR study

Alkylpropiolate having n-hexadecyl moiety in the ester group was stereospecifically polymerized with a [Rh(norbornadiene)Cl]₂ complex catalyst in alcohol to give rise to cis-transoid polyacetylenes in high yields. The unusually facile cis to trans isomerization for the polymer was found to be induced when the polymer was warmed to even less than ca. 57°C. Under these conditions ESR spectra bearing hyperfine structures due to the radicals generated by the rotational scission in the cis–π bond were observed. This isomerization induced a large g value shift in the ESR spectra together with an increase of the radical concentration during the isomerization, indicating formation of planar conjugated trans sequences that stabilize mobile unpaired electrons as solitons. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2457–2461, 1998     

ChemInform Abstract: Si60 Clusters: AM1 Computed Ih/C2v Relative Populations

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Synthesis of Hyperbranched Polysaccharide by Thermally Induced Cationic Polymerization of 1,6-Anhydrohexopyranose

The thermally induced cationic polymerizations of 1,6-anhydro-β-D -glucopyranose ( 1a ), 1,6-anhydro-β-D -mannopyranose ( 1b ) and 1,6-anhydro-β-D -galactopyranose ( 1c ) as a latent cyclic AB₄-type monomer were carried out using (S-2-butenyl)tetramethylenesulfonium hexafluoroantimonate ( 2 ) as an initiator. The solution polymerization in propylene carbonate proceeded without gelation to produce the water-soluble hyperbranched polysaccharides ( 3a-c ) with controlled molecular weights and narrow polydispersities. The degree of branching (DB), estimated by the methylation analysis of 3a-c , was in the range of 0.38 – 0.49. The thermally induced cationic polymerization of 1a-c using 2 is a facile method leading to a hyperbranched polysaccharide with a high DB value.