Abstract: A polymer with a hydrolytically labile backbone and having the structure: ##STR1## wherein R.sub.9 is an alkyl, aryl or alkylaryl group with up to 18 carbon atoms having a pendent carboxylic acid group or the benzyl ester thereof;R.sub.12 is an alkyl, aryl or alkylaryl group with up to 18 carbon atoms having a pendent carboxylic acid ester group selected from straight and branched alkyl and alkylaryl esters containing up to 18 carbon atoms and ester derivatives of biologically and pharmaceutically active compounds covalently bonded thereto, provided that the ester group is not a benzyl group or a group that is removed by hydrogenolysis;each R.sub.7 is independently an alkylene group containing up to four carbon atoms;A is selected from: ##STR2## wherein R.sub.8 is selected from saturated and unsaturated, substituted and unsubstituted alkyl, aryl and alkylaryl groups containing up to 18 carbon atoms;k is between about 5 and about 3,000; andx and f independently range from zero to less that one.