Hi polymer experts,
in our certain case, we analyzed poly(ethylene glycol) (PEG) with high performance size exclusion chromatography (HPSEC). Solvent was 10x PBS (aqueous solution).
For instance, we analyzed PEG with molecular weight (MW) of 40000 and 4 different architectures: linear, Y-shaped ("3-arm"), star-shaped ("4-arm") and 8-arm. These polymers elute at different elution times (not such a huge difference, but still there is a difference). The architecture has an effect on the size of the polymers in solution, e.g. the linear one will be more bulky while the 8-arm will be more compact and therefore elute at a later time point, although they have the same MW.
So is there any formula around to predict that behaviour? Since PEG is widely used, there my be something for PEG only in different solvent systems. We do not want to get the MW from the elugrams (we get it with MALDI), just want to explain the differences with a scientifically approved model, if there is one.
Thanks a lot for your help!
Marcus
This migth be helpful:
http://onlinelibrary.wiley.com/doi/10.1002/pola.10366/abstract
http://ac.els-cdn.com/S0032386103000302/1-s2.0-S0032386103000302-main.pdf?_tid=3669d00a-a723-11e6-a93a-00000aab0f27&acdnat=1478768216_74f26cb2ba208ff5f61f2b3b504cfb2b
HI Marcus,
This is an interesting question. I have a similar problem in which I need to work out the density of IP3 (inositol triphosphate) so my first thought was how accurate I need the volume calculation? then I though the radius of gyration could be used (see attachment). In my case a simple sphere may work. In your case due to the different topologies a cylindrical topology might be more appropriate. I hope this helps
You can calculate the hydrodynamic radius from Debye-Mie theoretical calculation from light-scattering measurments.
I suppose it must be related to the conformation of molecules and thus on how they pass-through on molecular sieves.
Hope to have been of some help
There are two ways to tackle this problem:
1. For a variety of architetures the ratios of radius of gyration (sometimes even hydrodynamic radii) of the branched polymer is calculated relative to the size of the linear polymer at the same molar mass (typically called g or g').
Knowing the Mark-Houwink Exponent (a) of the linear polymer and the g or g' ratio of your structure , you can estimate the molar mass of the coeluting linear polymer
Mlinear=MBranched(g')^(1/(1+a))
(That is published somewhere, if requested I'll find the reference).
Since you now know the molar mass of the coeluting (in SEC) linear polymer, the hydrodynamic volume is proportional to
(eta)lin*;Mlin=K * Mlin^(a+1)=K*g'*Mbranched^(1+a)
2. Alternatively, the answer to the Problem you raised (how large is the GPC/SEC shift for stars and linear polymers has been given by simulation
Here is the reference
Simulation of GPC-Distribution Coefficients of Linear and Star-Shaped Molecules in Spherical Pores: Comparison of Simulation and Experiment
Wolfgang Radke · Johannes Gerber · Gabriele Wittmann
Feb 2003 · International Journal of Polymer Analysis and Characterization
Hope this helps.
Regards
Wolfgang
Hi all,
thanks a lot for your very valuable replies, that helped me a lot! Since there are much more question followers than respondents, I assume this is helpful for many others as well.
Marcus
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