Xavier and all, may I remind everybody again (please forgive me I am tired doing so): polyaniline CAN NOT BE SOLUBLE, no conductive polymer is soluble. for using GPC in order to determine molecular weight, the polymer needs to be dissolved, truely dissolved.

I have published a big paper years ago and also during this discussion here, I have cited the paper, but I (not for the first time though)get the impression, people prefer to simply stick with prejudice, with pre-formed opinions rather to really deeply study a topic, which in this case involves to read about some relatively complicated topic: what is the difference between a solution and a dispersion?

Let me simply tell you, the difference is as big as is between plus and minus, day and night, black and white, dead and alive.

I suggest you study this:

http://www.bernhard-wessling.com/pani/www2/Research/soludisp/

After studying, you can comment, you can ask any question, I will answer all of them.

What you do by adding your MEA or other amine, is: you improve the dispersion quality / stability, but you do not help dissolving. When commenting on my article, please take the thermodynamic arguments serious: under which conditions a material can be dissolved?

Moreover, anyone is invited to run any of the experiments I have suggested which would prove that I am wrong, would prove that polyaniline could be soluble. Try to prove me wrong, not by words, by experiment, by facts! I have described all the experiments and facts which lead me to the conclusion that polyaniline can not be soluble. Only facts should be used in a discussion about this topic, not assumptions, beliefs.

I think light scattering method can provide the information you need but only its weight average molecular weight (Mw) not the number average molecular weight (Mn). I recommend you one reference: http://pubs.acs.org/doi/abs/10.1021/ja055327k

you can use scattering method. you can use dynamic light scattering instrument, Zetsizer nanoZS . Please see the attached file

Thank you for your valuable suggestions

one of the most used technique is to dissolve PANI in NMP- 1% LiCl solution and then use GPC instrument.

Then which coloum I have to use?. Is NMP coloum available?

You can try one more thing. De-dope the conducting form. Now it dissolves in a few more solvents. Even if it doesen't dissolve, dissolve in a small amount of NMP and add excess solvent which you use for the GPC.

THF column is available in many places. EB form, I think, dissolves in THF..try doing this one..

These are just suggestions...

All, I am sorry to disagree with all your comments. For a molecular weight measurement using GPC, you need to have true solutions. Polyaniline is definitely not soluble (also EB is not):

http://www.bernhard-wessling.com/pani/www2/Research/soludisp/Welcome.html

All the values which are published based on GPC measurements merely only reflect the residence time of the dispersion (which contains nanoparticles) in the column, hence they tell you something about the degree of dispersion.

Please also have a look here:

http://www.mdpi.com/2073-4360/2/4/786 (most recent update about my understanding of the Polyaniline structure)

Thank you for the comments..I will come back to you with my doubts (if any) after reading your page...I haven't tried doing what I said..Those comments were just suggestions as I mentioned. I have to check whether EB form dissolves/disperses in THF....

You can also use MALDI-TOF mass spectrometry to determine molecular weight (Mn and Mw) of polymer. Note that a slight underestimation exists for polydisperse samples.

http://www.springerlink.com/content/x701m878142n52th/

GPC in NMP LiCl is accepted method

Is an accepted, but nevertheless wrong method

I respecfully disagree with famous Dr. Wessling as he is not a polymer chemist. Viscosity experiments clearly show polyelectrolyte effect (expansion of polymer coil as resul of dilution). LIght scattering confirm this result. Nano-particles do not epand as result of dilution or acid doping. So, NMP-LiCl or meta cresol are pretty good solvents that help to show typical polyelectrolyte effects that are not known to colliid science. I agree that colloid particles do not show much tight coil to expanded coil transitions. All the best.

sorry, how can you assume I am not a polymer chemist? sorry, the only Polyaniline which is REALLY in the market, has been developed by me. Polyaniline is definitely not soluble, hence its MW can not be determined by GPC. What you see with addition of LiCl is not expansion of polymer coils, but co-aggulation of small nanoparticles into bigger ones.

if you and other readers like to spend at least a few minutes for reading (about what took me years of reasearch and months of writing it), then look at this:

http://www.mdpi.com/2073-4360/2/4/786

http://www.bernhard-wessling.com/pani/www2/Research/soludisp/

But anybody can believe what they like to believe, and you can deliver also wrong results for publication, but never for a real performance challenge in real mass production markets. That's what we do.

Again I have the same doubt, To use GPC as a tool to measure molecular weight of polyaniline in NMP+ Licl , which coloumn I have to use? Is NMP coloumn available?

NMP column is available in Central leather Research Institute (CLRI), Chennai..I presume....

You can determine Molecular weight of polymer by using GPC.

Sorry, it seems you did not read the previous comments, maybe you first read and then comment again? How about this?

I agree with Wessling, it is not possible to determine MW of PANI by GPC. PANI is not soluble in NMP, it is only dispersion.

MacDiarmid used DLS to measure Mw of PANI.. see this paper in JACS:

DOI: 10.1021/ja055327k

But Dr. Wessling raised some serious questions about utility of DLS in Mw measurements (section 4.1.1)...

Section 4.1.1 can be found here:

http://www.bernhard-wessling.com/pani/www2/Research/soludisp/Welcome.html

moreover, Section 5 of that paper elaborates why I claim polyaniline can not form true solutions, but dispersions (nanoparticles dispersed in a liquid), hence its molecular weight can not be determined by methods which are usually applied for polymers in true solution (DLS; GPC)

methylpyrrolidone frozen at -22 C. You can try to determine the molecular weight of polyaniline by cryoscopy. However, we must find a cryoscopic constant methylpyrrolidone. The method works for not too high molecular weight polymers. By the way - what method you get polyaniline? Well, if this is not a trade secret :-)

I tried to determine the molecular weight of un-doped polyaniline by GPC. I tried both DMF and THF column. It is partially soluble in THF and DMF. GPC results showed a low Mw (~1000 Da). I think its oligomers are only soluble and the chains with higher Mw are not soluble in THF.

according to my studies, also un-doped polyaniline is insoluble in both DMF and THF. Different polymerisation lots (if not polymerized and un-doped under extremely precisely controlled conditions) will result in different particle size in various solvent based dispersions. This may lead to the assumption of "solubility" or "partial solubility", but if you measure particle size, you will see: these are true dispersions, no solutions.

The solubility of many polymers in DMSO can be improved by addition of a small amount of Alkanolamines like monoethanolamine (MEA) and triethanolamine. At relatively low levels (5 wt%) they can help DMSO act more closely like NMP. May be this can open your options (NMR end group analysis ? good luck :-) ).

If your polyaniline is really soluble, it will be most likely low MW / oligomers.

Xavier and all, may I remind everybody again (please forgive me I am tired doing so): polyaniline CAN NOT BE SOLUBLE, no conductive polymer is soluble. for using GPC in order to determine molecular weight, the polymer needs to be dissolved, truely dissolved.

I have published a big paper years ago and also during this discussion here, I have cited the paper, but I (not for the first time though)get the impression, people prefer to simply stick with prejudice, with pre-formed opinions rather to really deeply study a topic, which in this case involves to read about some relatively complicated topic: what is the difference between a solution and a dispersion?

Let me simply tell you, the difference is as big as is between plus and minus, day and night, black and white, dead and alive.

I suggest you study this:

http://www.bernhard-wessling.com/pani/www2/Research/soludisp/

After studying, you can comment, you can ask any question, I will answer all of them.

What you do by adding your MEA or other amine, is: you improve the dispersion quality / stability, but you do not help dissolving. When commenting on my article, please take the thermodynamic arguments serious: under which conditions a material can be dissolved?

Moreover, anyone is invited to run any of the experiments I have suggested which would prove that I am wrong, would prove that polyaniline could be soluble. Try to prove me wrong, not by words, by experiment, by facts! I have described all the experiments and facts which lead me to the conclusion that polyaniline can not be soluble. Only facts should be used in a discussion about this topic, not assumptions, beliefs.

Shrikant, you also - like several people discussing here - seem not to have read my previous comment, nor my article.

- first, the topic of this discussion is not how to process polyaniline in DI water, but how to measure molecular weight, and I explained that one can not measure moleculare weight by using GPC

- second, when using DBSA, you are also preparing a dispersion of polyaniline in water.

http://www.bernhard-wessling.com/pani

Http://pubs.acs.org/doi/pdf/10.1021/ma970047d

If it's soluble in NMP, titrate the free amine content and run a blank on the NMP.

You may use rheology to estimate Mw. By generating shear viscosity versus shear and exlaborating to get zero shear viscosity, you may get some feeling about how large is the Mw since viscosity is strongly related to Mw. For linear polymers one may apply M-H equation to estimate Mw... good luck

Are you tried MOLDI-ToF spectroscopic technique ? I think it may solve u r problem

Fares, your suggestion is only valid for true polymer solutions. I can only repeat over and over: polyaniline is not soluble; in case of dispersions, the rheology / viscosity is strongly dependant upon particle size (i.e., at a given concentration, let's say 1%, a dispersion with prticles of 1 µm diameter is very low, if 100 nm, viscosity increases strongly, and a 1% dispersion with polyaniline particles of 10 nm size is a gel, not fluid any more.

See http://www.bernhard-wessling.com/pani/www2/Research/soludisp/

Palanirajan's suggestion is appropriate, the technique is called MALDO-ToF.

Yes, MALDI-TOF Mass spectrometry requires only pure compound. No need to dissolve in solvent.

To Bernhard Wessling. When I was reading your article came upon this statement: -" Every Na+ "tries" to have 6 Cl- around itself, and vice versa, leading to the well-known octahedral crystal structure.

Should not NaCl crystal have a cubic structure? I can even grow and send to you perfect cubes from solution :)

Thank you

yes, sure, Gary, Na+Cl- will grow perfect cubes from solution. However, on the surface, every NaCl crystal is not perfect at all!

I hope you caught the message: I am using the example Na+Cl- for showing 2 different aspects:

a) charges need to have countercharges, but that is not all of it - they also need to be shielded! (i.e., you can not grow a Na+Cl+Na+Cl+Na+Cl- single nanofibre, because for any Na+, it is not sufficient to have a Cl- counterion, because if this sits on the "right" side of the Na+, all the left and top and bottom side of the Na+ is "open", requiring to shield these charged sides as well; therefore, every Na+ is surrounded by 6 Cl-, and vice versa;

- this is not possible with linear conductive polymers; therefore, a completely different structure is formed, please look at

http://www.mdpi.com/2073-4360/2/4/786

b) at surfaces (even more at edges), any crystal is not perfect, the crystal symmetry is disturbed at the outer surfaces; therefore, any surface even of perfect crystals does not have the same composition as the elemental analysis shows for the pure compound.

Is PANi completely soluble in NMP? If it is soluble we can determine the Molecular weight by standard method for example light scattering technique, I thing your PANi is partially soluble in NMP

interesting comment, interesting because it creates a question in my mind: how is it possible to join a discussion like this without having read previous comments?

I suggest you read this:

http://www.bernhard-wessling.com/pani/www2/Research/soludisp/

PAni is completely insoluble. If you "think" it is partially soluble, then please deliver experimental evidence. Don't contribute assumptions.

It is serious problem and really difficult task:

Article Polyaniline Synthesis Catalyzed by Glucose Oxidase

By using Gel permeation chromatography (GPC)

Artur, it seems that you (like several other people, look what I wrote as an answer to Radakrishnan) don't read any previous comment before adding yours. Please check my comments further up from earlier time. GPC is not possible to be used, better to say: it gives you meaningless results! Please check above why.

Have you try SEC (steric exclusion chromatography)?

I suggest you applied dialysis paper 10 Dalton

sorry, as far as I understand how this works: also for dialysis paper you need to have true solutions. The mechanism is more or less identical with GPC. As Polyaniline does not form true solutions (but can be dispersed), you do nto get any information about MW, but some information about the adsorption / desorption kinetics.

Again I suggest to study this:

http://www.bernhard-wessling.com/pani/www2/Research/soludisp/

To Bernhard Wessling, i would like to know, in order to produce PANI/Graphene nanocomposites, polyaniline (emeraldine base) mix with graphene and NMP will have similar result as insitu polymerization of aniline monomer add with graphene?

John Lee, I have never tested this specific approach, but I would assume (from my experience): it is NOT AT ALL THE SAME. If you want a really optimal graphene / polyaniline composite, you better run in situ polymerisation, but also take care of temperature control and final rinsing.

Can you melt polyaniline? If you can, you may try use rheometer to get it viscosity then to estimate its Mw.

Otherwise, if you can add any funtional groups in the end of polyaniline, try to do solid state NMR to calculate the ratio of monomers and end functional groups, then you can get the number of repeating units for Mw.

Polyaniline is not moldable at all.

MALDITOFF is the only technique which will give you reliable results, and you will be surprised how low the MW is.

Poly aniline ishaving basic gp we can use acidic med solvent

By light scattering method

A very good technique to do this is the Small Angle X-rays scattering. Polymers such PAni are typically well studied by performing experiments at q range between 0.03 and 0.3 A-1. If you take a sample from a diluted solution containg the polymer and a sample from the buffer, you can use free data treatment softwares available on internet to determine the radius of gyration from which you can extract the molecular weight.

Saroj Madaan and Emerson Silva, my answer goes to both of you although you propose different approaches: both of these approaches require that Polyaniline would be truely soluble, like PS is in MEK, or PSSH in water.

But Polyaniline is not soluble, therefore both of your methods can not be used, and any results they deliver do only describe the particle size of the *dispersed* polyaniline.

I have already exüplained this above. You can easily look up my publications on this topic, e.g. here:

https://www.researchgate.net/publication/235919086_soludisp?ev=prf_pub

look for more here:

https://www.researchgate.net/profile/Bernhard_Wessling2/?ev=prf_act, go to

"Can Conductive Polymers be truely soluble? or will they form dispersions?"

Data soludisp

My opinion is, only MALDI-TOFF can give reliable answers, I already wrote this above as well.

I have problems with MALDI-TOF to find out good solvent for polymers, matrix, ZIP-TIP or UNZIP optimization, m/z interpretation. Highly appreciate to Bernhard Wessling if that you could have more detail suggestion for this problem?

sorry, I do not really understand your question; is it related to Polyaniline or generally to polymers of any kind? MALDI-TOF is not run from polymer solutions, but with dry polymer.

Solubility of polyaniline is really a problem. But I think solid state NMR can be used for the determination of molecular weight of PANI. Recently I found one paper on this also. I have not used it as it is not available here, if possible you can try.

I am totally agree with Prof. Wessling. One of my colleague is working with PANI and I have seen him dispersing the polymer before doing any characterization as it is not at all soluble in any solvent.

Souvik Ata, I am not a "professor" :-), just a simple chemistry doctor, but worked a lot on polyaniline and other conductive polymers and compounds.

Correct, conductive polymers are principally insoluble, as I have shown in this article (experimentally and theoretically supported):

https://www.researchgate.net/publication/202290125_Conductive_Polymer__Solvent_Systems_Solutions_or_Dispersions

which became a key part of a handbook chapter:

https://www.researchgate.net/publication/253651172_Conductive_Polymers_as_Organic_Nanometals

re solid state NMR, I do not believe one can derive information about molecular weight. As far as I see, only MALDI-ToF can help.

Article Conductive Polymer / Solvent Systems: Solutions or Dispersions?

Chapter Conductive Polymers as Organic Nanometals