[redskytonight820]

Hey all, i'm sorry i haven't been on much, this semester's crazy. I've run into another snag ... can anyone help me?

GPC of PMMA (poly[methylmethancrylate]) polymer:

Separation was made on PLGel universal column (styrene-divinylbenzene 100-10^7 separation range).

The RI detection, and eluent - THF, calibration is by polystyrene standards.

If the weight and number average values were calculated directly from the chromatogram, are the evaluated Mw and Mn values correct?

Here's what I'm thinking... since PMMA polymer falls within the range of the PLGel (100-10^7), then the values are approximately correct.

[Alpha-Omega]

Varian Application Note SI-01200:  A Reproducibility Study of the Online Monitoring of MW Distributions and Monomer
Conversion in a Free Radical Feed Copolymerization Reaction using PL-PMC Instrumentation

This note discusses a reproducibility study of a series of free radical feed copolymerizations, in or near real time, using a PL
polymerization monitoring and control (PL-PMC) system that utilizes rapid online gel permeation chromatography (GPC)
techniques.

Varian Application Note SI-01201 :  Online Monitoring of Free Radical Feed Polymerization Reactions using PL-PMC Instrumentation. 

A PL-PMC instrument with chromatographic monitoring in a GPC confi guration was used to make molecular weight measurements of the polymer synthesized throughout a solution-based free radical feed polymerization of methyl methacrylate.

Varian Application Note Application Note SI-01155:  Reproducible Online Monitoring of Molecular Weight Distributions and Monomer Conversion in a Free Radical Polymerization Reaction using PL-PMC Instrumentation.

This note discusses the reproducibility study of a series of free radical polymerizations, in or near real time, using PL
Polymerization Monitoring and Control (PL-PMC) systems that utilize rapid online gel permeation chromatography (GPC) techniques.

Thiese ANs utilizes the same conditions you have outlined.  I am attaching copies of the pdfs.  You may find it useful in interpreting your data/results.

[redskytonight820]

Thank you so much for all those PDFs .

So the general conclusion is: Yes, Mw and Mn values calculated directly from the chromatogram are correct?

[redskytonight820]

Yeah I don't really understand how to figure this out ... I found some equations:





But see, this is all assuming that PMMA fits in hte PLGel parameters. I mean, theoretically, if the PMMA fits the separation requirements for the column, then of course, the answer is yes... but I have no way of figuring out if it does or not

[DrCMS]

Let me see if i understand your question?

You've made some PMMA and measured the molecular weight by GPC against polystyrene standards. 
You've got Mn Mw etc. calcualted from the chromatogram obtained.

You want to know if those Mn Mw numbers are genuine?

Of course they're not you've tested PMMA against polystyrene.

However everybody doing GPC does the same so we all agree to ignore the error.

You'd need to do mass spec to get genuine molecular weights but thats a lot harder and more expensive.

Sometimes there are problems, an industrial process to make biodegradable polymers got cancelled after they found all the polymers made were not biodegradable although the initial work said they were.  The problem was that the monomer elluted at the same time as 10000Mw polystyrene standard and somebody got confused thought it was a 10000Mw polymer and sent it for biodegradeability testing which it past but when they actually made  polymers they found they did not biodegrade.

So quote the Mn Mw etc for your PMMA but always remember a mass spec will give you different numbers.

[redskytonight820]

Thanks everyone .

I think from all your help, and doing some search on the structures of THF, PMMA, and  polystyrene...

Polystyrene is hydrophobic
THF is slightly hydrophillic
PMMA is slightly hydrophillic

THF + polystyrene = large circular molecular blob
THF + PMMA = smaller circular molecular blob