[nazhasan]

I reacted acid terminated PLGA in DMF with 1,1′-Carbonyldiimidazole (CDI) to get the PLGA-imidazole intermediate. Then, N-Boc-1,4-diaminobutane (boc-DAB) was added to get second intermediate, can be named PLGA-boc-DAB. Finally, Trifluoroacetic acid (TFA) added to remove the boc. The TFA must be forming salt now and is present as PLGA-DAB-NH₃^{+ -}OOC-CF₃.

What can I do to get the pure PLGA-DAB with free amine group now? Everything is still in DMF which is the solvent I choose because my polymer has got good solubility in it. 

[baum0372]

PLGA should be soluble in other organic solvents like DCM.  My advice would be to to evaporate the DMF to get a solid.  Then suspend the solid in DCM (because of the TFA salt you probably won't be able to dissolve it).  Then, you can add sodium bicarbonate solution and extract the polymer into the organic phase several times.  Don't use NaOH as you can start to isomerize the lactic acid units and you will get PDLGA, so use only a weak base.  PLGA should not be soluble in water and so after evaporating your combined organic fractions you should have your pure PLGA.

An alternative option is to suspend the TFA salt in DCM and mix with Amberlyst A21 resin which is a weakly basic resin.  All the TFA will move to the amines on the resin and the DCM solution should be come clear.  After maybe 15-30 minutes stirring (depending on the amount of resin used) you can filter the mixture and then evaporate to get your pure product.

[nazhasan]

Thanks for the reply (a bit late though).
Can I use organic base to free the amine? For example, can I add triethylamine? I really don't want to work-up with water. And, at this moment, I can't get any resin.

I've seen papers where people used NaOH (in aqueous reactions) to break the salt into pure amine, so, may be TEA will do the same for me? Any thought??