Dear Sir. Concerning your issue about the convertion of polyethylene glycol PEG to monomethylether polyethylene glycol MPEG. The monomethyl ethers of PEG are commercially available and are frequently used as starting materials for the synthesis of other "mono" derivatives by substitution of the remaining hydroxyl group (refer to the section on Special Characteristics for a discussion of purity). Interestingly, Brunelle has shown that monoethers can be made selectively from hexaethylene glycol by proper choice of base and solvent. Shalati has published a well-described laboratory polymerization of ethylene oxide to produce M-PEG having a molecular weight of approximately 1200 daltons.I think the following below attached file may help you in your analysis:

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