The present disclosure provides brush-poly(glycoamidoamine)-lipids (PGALs) (e.g., polymers of any one of Formulae (I)-(IV)) and methods of preparing the PGALs. A described PGAL may include poly(glycoamidoamine)-derived moieties (e.g., such as which may assist the PGAL and/or a complex of the PGAL and an agent to pass through cell membranes or be taken up by cells. Also provided are compositions including a described PGAL and an agent (e.g., polynucleotide, small molecule, peptide, or protein). The present disclosure also provides methods, kits, and uses that include or involve the PGALs or compositions for delivering an agent to a subject, tissue, or cell and/or for treating and/or preventing in a subject a range of diseases, such as genetic diseases, proliferative diseases, hematological diseases, neurological diseases, immunological diseases, gastrointestinal diseases, respiratory diseases, painful conditions, psychiatric disorders, musculoskeletal diseases, genitourinary diseases, and metabolic disorders.