Addition polymerization of 5-norbornene-2-carboxylic acid esters using palladium catalyst system: Synthesis of monomers, effect of their stereochemistry on polymerization behavior

The effects of chemical structure of alkyl groups of norbornene carboxylic alkyl esters(methyl, octyl, 4-chlo-robenzyl) and endo/exo ratios of norbornene monomers on activity of palladium catalyst and polymerization behavior were investigated. Norbornene ester monomers were synthesized from the reaction of 5-norborene-2-carboxylic acid and various alcohols. Polymerization catalyst, di-μ-chloro-bis(-methoxybicyclo[2, 2, 1]-hept-2-ene)palladium(II) (DCBMP), was synthesized according to the literature procedure and silver hexafluoroantimonate (AgSbF₆) was used as a conjugate anion source. Gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning cal-orimetry (DSC) were the principal techniques for polymer characterization and ¹H NMR spectroscopy was used for chemical structures determination of monomers and polymers. For all of the norbonene alkyl esters GPC data showed that when the amounts of endo isomers exceeded those of exo isomers decreased molecular weight polymers were obtained probably due to the decreased catalyst activity. Polymerizations were conducted by varying the monomer/catalyst mole ratios (100:1, 200:1, 300:1). When 300:1 monomer/catalyst ratio was employed it was possible to synthesize high molecular weight (M_n=27500 g/mol), film forming polymer from exo-norbornene carboxylic acid octyl ester.