Have you considered using Fourier transform infrared spectroscopy (FT-IR) or X-ray photoelectron spectroscopy (XPS). NMR is a good technique for determining strucutre but atleast FT-IR will tell you which functional groups are present.

Is it possible to cleave and/or dissolve the polymers? It is very difficult to get info about polymer structure not in solution - you can determine chemical functionality by FT-IR or XPS as suggested above, but can't determine important polymer properties like Mw.

How much is known about the polymer ?

IR / Raman is a good first choice, as it provides basic information about the functional groups that may be encountered in the polymer and, hence, what measures can be taken so as to avoid damaging the coating.

You can try and exploit solubility of the polymer in common organic solvents for a relatively efficient separation procedure. If this does not work, an alternative is etch the magnetite particles out, leaving polymer nanospheres, however, this requires the polymer coating to be permeable.

If the polymer coating is not strongly insulating, electrochemical methods could be used to reduce the magnetite particles to FeO / Fe and strip them of their magnetic properties, for NMR study.

http://www.nanocon.eu/files/proceedings/nanocon_11/lists/papers/1311.pdf

Thanks a lot all of you for your reply. I would like to ask to Tomasz Jarosz. We know quite a lot about the polymer except the particular position of some functional group.Your idea of electrochemical method is more interesting. Do we any literature about it. What is your opinion, polymer would be effected?   

There are few works on the electrochemical treatment of magnetite nanospheres, however, dissolution of magnetite has been studied electrochemically. Enclosed, please find a work concerning the dissolution of magnetite in a number of systems. Based on these findings, a procedure for electro-assisted dissolution may be formulated (taking into account a drop of potential across the polymer coating).

The range of applied potentials, utilised for dissolution of magnetite is relatively narrow, therefore, most organic bonds should remain unaffected. Redox-active functional groups may undergo electrochemical reactions, however, apart from that, the polymer should not be affected.The factor most likely to affect the polymer would be the nature of the electrolyte used fo facilitate dissolution of magnetite, as some electrolytes (such as EDTA) may react with the functional groups of the polymer.

Article An Electrochemical Investigation of the Dissolution of Magne...

You can also use spectroscopic methods like in this paper

Article Electrochemistry and surface-enhanced Raman spectroscopy of ...