Cholesterol-PEG-MAL (MW 2000) is a PEG derivative and can be used to prepare liposome or nanoparticle due to its ability to self-assemble in water. The maleimide moiety is reactive with thiol molecule to form a covalent thioether bond.
References:
[1]. Juliano R L, et al. Liposomes as a drug delivery system for antisense oligonucleotides[J]. Antisense research and development, 1992, 2(2): 165-176.