Cl-PEG4-acid（Cat No.:I044715）is a bifunctional polyethylene glycol (PEG) derivative featuring a terminal chloro group and a carboxylic acid. The PEG4 spacer provides hydrophilicity, flexibility, and biocompatibility, making the molecule useful in biomedical and pharmaceutical applications. The chloro group enables nucleophilic substitution reactions for further functionalization, while the carboxylic acid allows conjugation to amines or other reactive groups through amide bond formation. Cl-PEG4-acid is commonly employed in the synthesis of drug conjugates, biomolecule labeling, and surface modification of materials, enhancing solubility, stability, and biological compatibility of complex molecular constructs.