Compositions comprising linear PNAI, cyclic PNAI, linear PEI, and/or cyclic PEI, useful for delivering compounds or substances into a cell, are provided, as well as methods of making linear PNAI, cyclic PNAI, linear PEI, and cyclic PEI. Also provided are methods of using compositions comprising linear PNAI, cyclic PNAI, linear PEI, and/or cyclic PEI for introducing substances into a cell.