I'm preparing polyflourinated polyether-polyphenylene block copolymer using Ulmann Reaction (Ni(cod)2). and I prepared it many times befor and it was Ok. but this time New peaks appeared in 19FNMR and some peaks in 1HNMR shifted to higher field and the ohers to lower field. Also GPC showed different peak intensity but at the same retetion time. and the colour of the material was dark more than usual.
I dont Know if crosslinking happened or what? (Because I separated it by methanol and hydrochloric acid).
Crosslinking is very unlikely, since the product is still soluble (GPC)
Darker coloration indicates more likely to formation of double bonds than cross-linking. New appearance of Lower field signals can be related to protons attached to double bond carbon. Since you are working with fluorinated organic compounds with exposure to light may cause formation of double bonds by releasing HF. This can be easily tested by pH control from the wash water of the polymer after purification to eliminate the presence of the HCI used in the previous reaction. If you could also perform a FT-IR and C-13 NMR they will provide more evidence to the idea above or the alternative ones. Similar reaction occurs with the PVC.
as Helmut says, crosslinking unexpected since same retention time.
you can look at the polydispersity also: if unchanged, no crosslinking, if increased, thus maybe crosslinking and some chain scissions ...
Please try also MALDI TOF to evaluate the change of mass during the treatment
Dear All, Thank you very much for your valuable answers.
I would like to add that polydispersity from GPC fro (Mw/Mn = 62.5) and befor that it was much smaller about 12-15. May be that mean crosslinking.
Regarding the answer of Dr. Kerem, I would like to say that the elemination of HF may be difficult because I use decaflouro-bi-phenol.
Thank you very much for the compliment but i am not a doctor yet. :) It will be my pleasure, If it could be helpful to you.
GPC data is depended on the retention time of the polymer in the column, so it can not show you the exact chemical change in your product. As Prof. Ritter mentioned before if there were any cross-linking the solubility of your product wont be sufficient enough while feeding the sample to the column. Even the physical appearance of the product would be totally different (not only the color-flocculent or at least mud). My advice is still valid, please check your spectroscopy data. Especially, by tracking the specific signal shifts. Good Luck.
Crosslinking lead to increase in hardness/brittleness of the materials. Based on the description, I believe extent of crosslinking is small as material is soluble but shows higher polydispersity. To determine the extent of crosslinking, measure the undissolved weight in a solvent.
I agree with Dr. Ranjan Kamat that a crosslinked polymer will become insoluble. I may also add that it will become in-fusible possessing the characteristics of a thermoset. When a polymer becomes dark in color, then one may consider either the possibility of oxidation or some degradation and any of these is indicative that the the reaction has undergone a different path.
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