Patent ID: 8637711

Claim:
A method for selectively making specific discrete (polyethylene glycol) (dPEG) compounds containing a discrete and predetermined number of ethylene oxide moieties, which comprises the steps of: (a) forming a reaction mixture comprising a first dPEG compound having the general structural formula I or I′: R 1 - d PEG x -OH I R 1 - d PEG x -OR 2 I′ and a dPEG compound having the structural formula X or X′, respectively: R 3 - d PEG y -OR 2 X R 3 - d PEG y -OH X′ (b) adding a non-sodium ionizing agent, which is potassium t-butoxide, in the presence of a catalyst and under conditions to produce a dPEG compound having the structural formula XI R 1 - d PEG x+y -R 3 XI; wherein said potassium t-butoxide ionizing compound is added to a reaction mixture of compounds I and X and II, or I′ and X′, at a rate that is about equal to the rate at which compound XXII formed in situ from compound I reacts with compound X or the rate at which compound XXII″ formed in situ from compound I′ reacts with compound X′, respectively, wherein: R 1 - d PEG x -O − M + XXII R 3 - d PEG y -O − M + XXII′, wherein, R 1 and R 3 each independently are one or more of a hydroxy protecting group (PG), a functional group (FG), or a protected functional group; R 2 is a leaving group, x ranges from about 1 to 300, and y ranges from about 1 to 300.