A new heterobifunctional (succinimidyl carbonate, SC)-activated poly(ethylene glycol) (PEG) with a reversible 1,6-elimination linker and a terminal alkyne for "click" chemistry was synthesized with high efficiency and low polydispersity. The α-alkyne-ω-hydroxyl PEG was first prepared using trimethylsilyl-2-propargyl alcohol as an initiator for ring-opening polymerization of ethylene oxide followed by mild deprotection with tetrabutylammonium fluoride. The hydroxy end was then modified with diglycolic anhydride to generate α-alkyne-ω-carboxylic acid PEG. The reversible 1, 6-elimination linker was introduced by conjugation of a hydroxymethyl phenol followed by activation with N,N'-disuccinimidyl carbonate to generate the heterobifunctional α-alkyne-ω-SC PEG. The terminal alkyne is available for "click" conjugation to azido ligands via 1,3-dipolar cycloaddition, and the succinimidyl carbonate will form a reversible conjugate to amines (e.g. in proteins) that can release the unaltered amine after base or enzyme catalyzed cleavage of the 1,6-linker.