Hi there, I have a polyelectrolyte polyethylenimine (PEI) grafted with DSPE-PEG (lipid-polyethylene glycol). I have some problem in calculating the grafting density. I do that by the integral of the two polymers.
It does not dissolve (not a clear solution) in CHCl3, CH2Cl2, MeOH, DMF. OK in water (clear after heating/sonication) and good in DMSO. But the peak of DMSO (2.5) overlap with the peak of PEI (2.4-3.3).
In water, the peak of the lipid is very bad and it is not "right" (coz it is with PEG and the ratios between PEG and the lipid should be fixed, but it is NOT). Also, I found that the ratios between the PEG and PEI are DIFFERENT before heating and after heating with a heat gun! (yes, some of them will dissolve well, in a clear solution without heating)
I tried to use D2O/Acetone to dissolve the stuff and I got a peak of the lipid more than the PEG while the ratio between PEG and PEI are the same as those in water.
What should I do?
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NMR integral of Hydrophobically modified polyelectrolyte
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