it depends on the MW. If you can see the resonances of terminal units ( usually in polymers they have a slightly different Chemical shift) you can try to make the calculation of MW from the ratio of their integral with respect to that of the CH2 units of the polymer , Otherwise a DOSY 2D experiment may give an estimate of the molecular Diffusion from which you can derive the MW by the Stokers Einstein equation.

For higher molecular weight samples, it is tedious task to determine the molecular weight with NMR for these one should opt GPC method.

you should convert the alcoholic endgroups into esters by reaction with (non proton bearing) derivatisation reagents like trichloroacetic anhydrid or trichloroacetyl isocyanate. See: Polymer Bulletin 1991 , 27, 201-204

Best regards and good luck

Gerhard

terminal ethylene oxide units do not have a sufficiently different shift in proton NMR at lower fields. 13C chemical shift for the terminal eo units are on the other easily identified. quantitative 13C NMR can be used to determine MW of lower MW PEGs. It is specially easy for liquid PEG's as they can be mesured at very high concentrations. High MW PEG's are more difficult as good signal to noise needs to be reach ed on terminal eo units to get good accuracy of MW.

Dear Gerhard,

thanks for the reference....I am only wondering why the derivatisation must not carry a hydrogen. If it would have a characteristic 1H signal (e.g. O-CH3 which is also present per-se in some PEGs user for protein pegylation) that also could serve as a quantification reference (maybe with DOSY filter) couldn't it?

Alfred

When using a non H-bearing derivatization reagent it can be added in excess directly into the NMR tube!

..ah, I see. Thanks Gerhard!

Alfred