Polypentenamers having pendant carboxylate groups including esters, acids, and salts and their[hydrogenated derivatives have been prepared and characterized, and some of. their properties investigated. Reaction conditions were established to control the amount of pendant thioglycolate groups incorporated into the polypentenamer by the free-radical addition reactions of thioglycolic acid derivatives and subsequently to com­pletely hydrogenate the polymers so formed, which contained thioglycolate contents ranging from less than 1 mole-% to about 16 mole-%, without backbone degradation and crosslinking reactions. The glass transition temperatures and the melting points of these polymers were observed to depend upon the pendant group content, as expected, but there appears to be little difference within these properties between polymers in which the pendant groups were in the salt form as compared to those of the corresponding car­boxylic acid form. The thermal stabilities of the polymers having the pendant groups were somewhat lower than those of the parent polymers, apparently because of side re­actions involving the thioglycolate groups. The calcium salt derivative showed a particu­larly low thermal stability compared to that of polymers with monovalent salts.