Hi,
I am trying to synthesize PLA with high molecular weight. The method that I have been using can give me at most 50kDa. Based on the paper I've been following, it should be able to increase more. I know that lower pressure gives better MW, but is there any paper that test on gradual increases?
As in, you consistently decrease the pressure every few hours instead of setting it at a certain amount and leave it be. Or is there barely any differences?
Added Info:
My PLA's goal is to be used as medical implant. I was interested in the diisocyanates' suggestion but I am not sure if trading higher Mw for bioabsorption will be good for me.
I have been using Tin Chloride and TSA as my catalyst in a melt and solid polymerization. This is based on Zhang's paper:
http://www.cjps.org/EN/article/downloadArticleFile.do?attachType=PDF&id=11239
However, I'm struggling in reaching his reported MW so I was wondering if I did something wrong (one of the few parameters I look at was Pressure).
This is really tricky reaction; it is all depending on your catalyst, Vacuum pressure etc. I did this reaction with different condition for many times. But it always results around 50 kDa. It is very difficult to increase the molecular weight with this condensation. So after condensation reaction, you should go for solid stage polymerization. Please ref. this paper it have the different reaction condition for different molecular weight.
The PLA is hydroxy terminated. A trick to enlage molecular weight is to make a post treatment with diisocyanates like IPDI. The PLA is chain elongated by formation of urethane groups.
I agree with Burkhard Koehler, you can increase the molecular weight by chain extension. But this chain extension with IPDI/HMDI/TDI will suppress the bioabsorption behaviour.
Thank you Mr. Selvaraj for the paper and Mr. Burkhard for the suggestion on diisocyanates.
It is my fault for not providing clearer information regarding my problem. My PLA's goal is to be used as medical implant. I was interested in the diisocyanates' suggestion but I am not sure if trading higher Mw for bioabsorption will be good for me.
I have been using Tin Chloride and TSA as my catalyst in a melt and solid polymerization. This is based on Zhang's paper:
http://www.cjps.org/EN/article/downloadArticleFile.do?attachType=PDF&id=11239
However, I'm struggling in reaching his reported MW so I was wondering if I did something wrong (one of the few parameters I look at was Pressure).
I would also try Sn(Oct)2, tin dioctoate, alone and in a 1:1 mixture with TSA as catalyst. Another suggestion is bismuth neodecanoate (alone or in 1:1 mixture with TSA). Both can be bought from SIGMAALDRICH and could result in a higher molecular weight. Perhaps they work at a lower amount: 0.1-0.4 weight-%. You can also use carbonyldiimidazol as chain elongation agent, in doing so the carbonate ester is formed. This should be less critical for bioabsorption. For chain elongation experiments SnCl2 is the better catalyst, because the Sn and Bi carboxylates form partly dead ends (esters) at the polylactide.
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