Please try tert-butanol (low transfer constant) instead of 2-propanol (high transfer constant)

Dear Dumindika

I think that DMF as a solvent is not so good option. NIPAM may be very easily polymerized in the mixture of water and methanol. The more water you add the higher molecular weight you will obtain. However, by increasing the water content you may loose control over your ATRP process. You may try following reaction system: CuBr and PMDETA as a complex (1:1 molar) and the mixture of methanol and water (1:1 v:v) as a solvent. You have to keep the concentration of NIPAM on high level (2-4 M). The molar ratio of NIPAM to activating complex should be about 100:1. CuBr and PMDETA complex is very active so you do not need to heat it. If the PDI value will not be satisfactory you may lower the water content.  However, you should visit the website (http://www.cmu.edu/maty/matyjaszewski/) of prof. Krzysztof Matyjaszewski group who is the inventor of ATRP or read some publication of this author.

Regards

Karol

Thanks Karol for your comments, actually I tried water: 2-propanol mixture for ATRP and ARGET-ATRP at 00C as well as  at room temperature.  but the out put was not as expected. so with your suggestions, i would try to keep monomer concentration around 2-4 M. 

thanks

I think that it may help you. However, you may try to purify your monomer because NIPAM may undergo self-polymerization even in low temperature if stored long. Purified NIPAM should look as a white "fresh snow". If your NIPAM is in the form of lumps, it is definitely contaminated.

Please try tert-butanol (low transfer constant) instead of 2-propanol (high transfer constant)

Dear Karol,

I have made good experience with simple polymerization in  water, using sodium formate as a chain-transfer agent for molecular-wight control.  This is not as controlled as ATRP or RAFT, but it works to prepare mol. weights from typically 50,000 to 2,000,000 g/mol, with polydisperdity indexes from about 2 to 5.  Here's a reference:  S. Seiffert and D. A. Weitz, Soft Matter 2010, 6, 3184–3190.

Greetings from Berlin,

Sebastian Seiffert

Firstly, SEC lies (see http://dx.doi.org/10.1016/j.eurpolymj.2014.11.018  ). You can't trust any molecular weight from it unless:

(a) you've generated a correction factor from a series of known narrow polymers of the type being measured vs the calibrant

(b) you've a mass detector (typically viscometer and MALS) in series on the SEC.

Thus you need to independently find the Mn - typically by end-group titration by 1H-NMR, dilute solution visometry or some other means.

Second, let me take you to the dark side by suggesting living anionic polymerisation thus: http://onlinelibrary.wiley.com/doi/10.1002/pola.10518/pdf

Hello: I have synthesized PNIPAM polymer (Mn ~2000 g/mol) via RAFT polymerization in dry DMSO (using a trithiocarbonate RAFT Agent). The H-NMR confirmed the polymer synthesis and the UV @ 310 nm shows the RAFT end moiety attached to the polymer. The problem is precipitation of the polymer. I tried precipitation in cold diethyl ether solvent, however I get a milky suspension that looks turbid or colloidal and when I filter I do not get anything. Any suggestions ? It is puzzling me !

Likely there's simply too much solvent and anti-solvent, and the low MW PNIPAM is indeed a colloid. Try concentrating the solution before precipitating. It's a pain to vac down DMSO, but it is doable.

I did concentrate it. But you know it is very hard to totally remove all the DMSO. Does the precipitant solvent need to be cold ANHYDROUS Diethyl ether ? or cold normal diethyl ether is fine ? Also How about trying cold hexane ?

It might be your RAFT agent that's the issue. For oligomers (and this is ca. DP = 17) the end-group can significantly alter the solubility properties.

I'd consider dialysing it with a very low MWCO dialysis membrane* and then lyophilising.

*Such as https://www.coleparmer.com/i/spectra-por-131054-ce-dialysis-tubing-500-mwco-16mm-10-2mm-33ft/0289906

Another smart idea I've heard but never tried, which if you have a centrifuge with a thermostat is possible, is dissolve in water and heat above the LCST. Then centrifuge above the LCST. The PNIPAM should phase separate, but the impurities stay in solution.

You did not mention the target Mn, perhaps this will help.

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