I used 150 g of L-lactide (liquid, stored in a fridge at 2-4 degr.C), 0,8 g of Sn(Oct)2 as a catalyst. I mixed L-lactide and Sn(Oct)2 in a glass, than placed the glass into an oven at 140 degr.C for 2 hours. There is no any stirring tool in my lab, so I used my own hands and a glass stick (every 5-10 minutes I stirred the liquid by the glass stick). When I got the glass from the oven and waited for 1 hour, nothing changed. It was a liquid. I wanted to get hard PLLA and do mechanical experiments, but it is a liquid... What did I wrong?
I got better results in caprolactone ring open polymerization when I carried out in inert atmosphere.
It is unfortunate that you don't have any stirring equipment and that you had to carry it out in an open glass in an oven. As Rodolfo said, it probably should be done under an inert atmosphere and probably using a solvent. Your mixture may be a liquid because it is a mixture of Sn compound, L-lactide and the poly lactide. It may be possible to extract product with a solvent and then reprecipitate it.
Here is a relatively recent paper using a zinc complex
Article Ring-Opening Polymerization of L-Lactide and epsilon-Caprola...
Lactide Polymerization Procedure
In a typical experiment (Table 1, entry 1), in a glovebox, a Schlenk flask was charged with a solution of complex 1a (8.58 mg, 13.87 μmol) in CHCl3 (2 mL) equipped with a magnetic stirring bar. To this solution was added rac-lactide (100 mg, 0.69 mmol, 50 equiv). The mixture was stirred at room temperature for 60 min. After a small sample of the crude solution was removed with a syringe to be characterized by 1H NMR spectroscopy, the product was isolated and purified by precipitation from dichloromethane by the addition of 5% hydrochloric acid in methanol. The polymer was collected and dried under vacuum to constant weight.
Rodolfo Piazza , Joseph S Merola Thanks for your advice! I will try to find nitrogen.
How do you think, can it be better if I use magnetic stirring equipment, but decrease the experiment temperature to 100 degr.C? I got a simple stirring machine, it can heat to 100 degr.C maximum.
@ Anastasiia Kashirina The lower temperature that I have used was 120 °C. I'm not sure if it is possible to react at 100°C.
My procedure is quite similar than Merola, however I don't carried it out in a solvente.
Article mPEG-co-PCL nanoparticles: The influence of hydrophobic segm...
Dear Anastasiia
Are you sure that you have used (l-Lactid)? because at ambient temperature, L-lactide is a white solid compound and not a liquid!? may be you have used l-lactic acid?
Harrane Amine , thanks for your attention to my question. I used 90% L-lactic acid, it is a liquid at ambient temperature.
Having a PLA with good mechanical properties (PLA with high Mn) is not possible with lactic acid due to the nature of the polycondensation reaction involved. In your case you must use lactid. Also you can modify your operating procedure and conduct the polymerization reaction in a suitable solvent and use an operating procedure including a hot plate (oil bath) equipped with magnetic stirring.
good day prof amine .
the best error in your PLA,,????????????it's Sn(Oct)2???????? no polymerization it's acidique medium ???????? you must use basic medium ( use base) ??????? lewis base or NaOH ,kOH ?????????
here you cane obtained your PLA (wite powder).
thank you
Your should remove the oxygen. reaction should be carried out under vacuum or protected by argon. I prepared PLA for thousands times. trust me, if your want to get high Mn of PLA, you should get high vacuum. if the low Mn is also acceptable, then remove the oxgen by argon, several times, then reaction proceeded under protection of argon. Make sure the oxgen are carefully removed.
Yanfei Hu
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