If you work with a polymer of widely known chemical structure but unknown molecular weight, the easiest way to evaluate MW is doing viscometry followed by calculations of MW by Mark-Houwink-Sakurada equation. To get the chain contour length, divide MW of the polymer by the MW of the monomer unit and multiply by the length of the monomer unit. Tell more of your system to get more adequate or detailed answers :)

If you work with a polymer of widely known chemical structure but unknown molecular weight, the easiest way to evaluate MW is doing viscometry followed by calculations of MW by Mark-Houwink-Sakurada equation. To get the chain contour length, divide MW of the polymer by the MW of the monomer unit and multiply by the length of the monomer unit. Tell more of your system to get more adequate or detailed answers :)

Polymers usually form random coils, therefore, the contour length, i.e. the maximum end-to-end distance of the polymer, which is probably what you think of when you talk about the length of a polymer will be of limited significance for the problem you've stated.

Nevertheless to calculate the contour length you have to multiply the number of reptition units (which you may estimate from the molecular weight) times the length of the repetion unit times the cosine of the ((binding angle theta-180)/2). The last step distingushes between maximum physically possible and the maximum length of the poylmer chain if you would just linearly add each individual segment.

Dear Mattias,

the contour length is a length of a polymer chain in a maximally elongated conformation, without deformation of valent angles. The average end-to-end distance is hydrodynamic radius of a polymer coil, i.e a different and more realistic measure. Let us better wait before Van Tran makes her problem clearer.

Alexander

Depending on the polymer species or functional groups, you can try for Size Exclusion Chromatography (SEC), I suggest to look for this service, they'll ask for all the available information regarding your polymer, in order to get the best/fast result.

Dear Dr. Ivanov,

I believe we are both right in this case. The contour length USED TO BE the maximum length of the polymer. But the definition changed slightly, so the current definiton takes the binding angles into account.

Please have a look here:

http://goldbook.iupac.org/C01308.html

So to avoid this disambiguity, people tend to say the old and new contour length. I omitted this, because I thought those little historical details may not be of interest for Van.

But you were completly right with the comment on the end-to-end distance, I forgot a maximum there, which I added now in the above answer. Of course the end-to-end distance is diffrent from the contour length. Maybe it might be interesting for Van to note that the quotient between end-to-end distance and contour length describes the degree of chain stretching, which is one for the maximum physically elongated chain, i.e. when the end-to-end distance becomes equal to the contour length.

Best

Matthias

Yeah, I also knew the Mw of my polymer by Mark-Houwink-Sakurada equation. That's right, you two did talk about the lenght but I 'd like to know how to calculate or search the coil length. We all may know the salt can effect to the length of polymer. But when we want to coat polymer on the surface of nanoparticles or mesoporous, I think we must use the coil length, do we?

Dear Matthias,

thank you indeed for your remark on the obsolescent definition. This was perhaps a scientific reminder of my ageing ... :) Could you please send me and other participants a link to the new definition? Thank you in advance. As follows from Van's answer, she is more interested in evaluation of the coil dimensions.

Best regards

Alexander

Dear Van,

if you wish to compare the sizes of pores or nanoparticles with that of your polymer coil, you should probably use its hydrodynamic radius. I understand you work with a polyelectrolyte in aqueous solution. The coil size will depend then on both the pH and ionic strength. The more ionized is your polymer the larger radius it will have. It will also increase at lower salt concentrations. I cannot conceive, however, an easy technique to estimate the radius. Static light scattering is reliable but quite laborious. May anybody suggest something easier?

Alexander

Dear Alexander,

as provided above a link from the IUPAC:

http://goldbook.iupac.org/PDF/C01308.pdf

There is says:

"The maximum end-to-end distance of a linear polymer chain. For a single-strand polymer molecule, this usually means the end-to-end distance of the chain extended to the all-trans conformation. For chains with complex structure, only an approximate value of the contour length may be accessible. The sum of the lengths of all skeletal bonds of a single-strand polymer molecule is occasionally termed 'contour length'. This use of this term is discouraged."

Best

Matthias

I all thank to A.Ivanov and Arras ^_^ In my Lab, I have DLS machine, I may chech the radius gyration and its dependence in pH and salt concentration. That's a good advice :)

You are welcome, Van. DLS may give you too approximate value of MW. What you get from DLS is a mean diffusion coefficient (D). Check if your program uses adequate formula to transfer D into MW. The best would be to find in the literature a scaling dependence of D on MW for your polymer and the solvent. Use diluted polymer solution to avoid polymer associates.

Best wishes

Alexander