Methods are provided for transfecting cells with large cargo using a poly(beta-amino ester) (PBAE) molecule, and achieving high efficiency and viability. A method is provided of transfecting cells with a cargo, by forming a complex of the cargo with a (PBAE) molecule, mixing the complex with a first buffer and contacting the complex with the cells, wherein the cargo has a dimension of at least 0.1 μm. The PBAE molecule may be formed by reacting an amine with a di(acrylate ester). In some aspects, the PBAE molecule is poly(1,4-butanediol diacrylate-co-4-amino-1-butanol). In some aspects, the PBAE molecule is capped with 1-(3-aminopropyl)-4-methylpiperazine.
