Separation and Transport of Macromolecules

Research People Equipment Publications

 

Research

"What's in a name? That which we call a rose
By any other name would smell as sweet."
W. Shakespeare: Romeo and Juliet (II, ii, 1-2)


The problems encountered by polymer scientists are frequently just the opposite from  those of Juliet – a multitude of “smells” can be found under the same name. The monomer, from which the polymer is produced and the name is derived, may consist of identical molecules, but they can connect in many different ways depending on the mechanism and conditions of polymerization. The properties of the resulting polymer strongly depend on the way in which the monomeric units are connected in the  macromolecule, especially on their number, i.e., on the molecular weight.
Not only can we find samples of a given polymer, e.g., polystyrene, with different molecular weights and therefore different properties (different “smells under the same name”), but we can find macromolecules of various molecular weights in one sample. The probability that we find a macromolecule of a certain molecular weight in a sample is a  function of the molecular weight, and the function is characteristic of the sample; each sample has its own molecular-weight distribution.
    Frequently, the average molecular weight obtained by standard methods, such as osmotic-pressure or light-scattering experiments, correlates poorly with the properties and behavior of the polymer systems if these are strongly affected by the presence of a low- or high-molecular-weight component. This is especially true if a polymer in solution is in contact with a semi-permeable membrane, as is the case in many industrially or biologically important processes (e.g., glomerular filtration).

 


 

        The department investigates various phenomena in which macromolecules are separated due to some specific properties, mostly directly or indirectly related to molecular weight. The methods of molecular-weight-distribution determination based on these processes are size-exclusion chromatography (also called gel permeation chromatography, GPC), asymmetric-flow field-flow fractionation (A4f), and MALDI-TOF mass spectrometry (MALDI-TOF MS). In GPC the macromolecules are separated according to their size while passing through a column packed with a porous gel. Small molecules wander more frequently and deeper into the pores, and thus leave the column at  a later time. A4F is governed by several mechanisms, depending on the size of the macromolecules or their assemblies.

The basic mechanism is as follows: the solvent flows through a narrow channel with a speed following a parabolic profile across the channel. The secondary perpendicular flow drives the macromolecules to stagnant solvent layers near the semi-permeable membrane at the channel bottom but this is opposed by diffusion. Smaller molecules with larger diffusion coefficients get more frequently into the faster-flowing layers of solvent and are thus washed out earlier. Both these separation methods are based on the size rather than molecular weight; therefore calibration is necessary. The second possibility is to analyze  on-line the molecular weight of the efflux with a suitable detector. In MS, charged particles are separatred in the electrical field according the ratio of the molecular weight and charge, according to the combination of the Coulomb and Newton laws. MS is thus, in principle, an absolute method for molecular-weight determination.


    The department deals both with the theoretical development of these methods and with their application to practical problems, especially those relevant to the research programs of the Institute. The objects studied include not only synthetic polymers but also their conjugates with biologically-active agents and various assemblies, if  these  are stable under  the conditions of separation. Examples are nano particles based on polylectrolyte complexes of DNA, conjugates of poly(ethylene glycol) with special peptides, comb copolymers of polystyrene-poly(tert-butyl(meth)acrylate), pseudopolyrotaxane of synthetic polymers and cyclodextrins, polyanilines etc.
    In a similar way, the department implements and also applies  other analytical methods, such as elemental analysis and gas chromatography in combination with mass spectrometry.


 

BIOpolymer POstdoctoral Laboratory and educational center - BIOPOL

Otto Wichterle Centre of Polymer Materials and Technologies - CPMTOW

Centre of Biomedicinal Polymers - CBMP

Centre of Polymer Sensors - CPS

Polymers for Power Engineering - Energolab


 

Institute of Macromolecular Chemistry AS CR, v.v.i.
Heyrovského nám. 2
CZ-162 06 Praha 6
Czech Republic
phone:+420 296 809 111
fax:+420 296 809 410

Strategie 21