I have been trying to separate sodium cyanoborohydride from peg, because I have done an amino reductive synthesis of PEG, but both compounds are insolubles in diethyl ether so when I tried to precipitate PEG also sodium cyanoborohydride precipitate
If diethyl ether doesn't dissolve your PEG product try some other organic solvent, my suggestion would be chloroform. Hopefuly PEG product will dissolve in CHCl3 while cyanoborohydride will not and you will be able to filter it out.