Biodegradable, anionic polymers derived from the amino acid L-tyrosine

A polymer with a hydrolytically labile polymer backbone, said polymer having the structure:

• ##STR17## wherein R.sub.9 is an alkyl, aryl or alkylaryl group with up to 18 carbon atoms having a pendent carboxylic acid group on 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 the group consisting of straight and branched alkyl and alkylaryl esters containing up to 18 carbon atoms and ester derivatives of biologically and pharmaceutically active compounds covalently bonded to said polymer, provided that said 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 the group consisting of:
• ##STR18## wherein R.sub.8 is selected from the group consisting of 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;
• and
• x and f independently range from zero to less than one.