Biodegradable poly(beta-amino esters) and uses thereof

A compound of the formula: wherein each r, is independently selected from the group consisting of hydrogen, C1-C6 short chain C1-C6 short chain, hydroxy, amino, alkylamino, dialkylamino, cyano, thiol, heteroaryl , aryl, phenyl, heterocycle, carbocycle, and halogen; n is an integer being 3 and 10,000; x is an integer between 1 and 10; and when X is methyl or NR2; and R is selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, cyclo, heterocyclo, aryl, and heteroaryl; or when X is OR; and R is selected from the group consisting of alkyl, alkenyl, alkynyl, cyclo, heterocyclo, aryl, and heteroaryl; and is an integer between 1 and 10; or when X is OR; and R is hydrogen, y is 5 or an integer between 1 and 2 or 6 and 10 and derivatives and salts thereof.