I am working on making of block co-polymers of Polyethylene glycol-polylactic acid? Does this formula Mn(peg-pla) = Mn(peg)+ [72*(Mn/44)*(EO/LA) ] This is one of the most widely used formula to calculate using Mn using NMR (as per literature)? I know EO/LA feed ratio ? Can anyone tell me whether it is the right way to calculate the average molecular weight of a polymer? kindly quote a suitable reference in this regard if possible ?
Thanks in advance
Mr. Vura,
Presumably there shuld be protocoles in the literature because of polymers' chemistry is well developing area.
Thanks for the reply Bojidarka B.Ivanova. i am looking for those protocols. in case you come across something related to the topic do post it .
I assume you make the blockcopolymer using PEG with a known Mn as starting material. Then you can indeed use this formula with Mn = Mn(PEG) and (EO/LA) = ratio of EO/LA in your polymer. You need to calculate this ration from the NMR, it is not necessarily the same as the feed ratio. You don't need a reference, it's simple maths. Mn(PEG)/44 = degree of polymerization (number of repeating units) of PEG. This multiplied with EO/LA gives you the degree of polymerization of the LA block.
Thanks Mr.Mathias Glassner for the reply .Can u explain why and how the DP(PLA)=DP(PEG)*(EO/LA) ratio from NMR does give Mn of PLA ? Can u explain how DP is related Eo/ La ratio? Also I would like to know whether this formula hold good to calculate or help predict the mol wt I need to get from reaction ? As I already have the feed molar ratios if I plug it in this equation will I end up getting the Mn (Theoretical)? (I know this is not valid but the confirmatory thing would be the mol wt from GPC )
You can find informations in this paper:
Polym. Chem., 2016, 7, 6918–6933
Hope it will be usefull.
Sorry, i made a mistake. The correct formula is DP(PLA) = DP (PEG) * LA/EO This is only correct if you make your blockcopolymer with PEG of a known DP as starting material. For Example DP(PEG) = 100. If your NMR shows LA/EO = 2, then DP(PLA) = 200.
Dear colleague
you are on the right path ???????? it is the proper form ??????? you can compare your mass with the results of the MALDITOFor the GPC ????????????
thanks
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