Khoa, before you go any further with your purification procedure, please keep in mind that the obtained triblock copolymer, synthesized under the given conditions, should have low molecular weight (Mn of ca. 2,400) and quite low glass transition temperature (below r.t.), in case of quantitative yield of the product. There is no information which lactide isomer you used. If L-lactide was used, the synthesized polymer would crystallize if precipitated, thus facilitating the purification by the dissolution-precipitation technique.

I have performed numerous syntheses of PEG-PLA copolymers with the use of all lactide isomers (L, D, rac, meso). I would recommend you dissolve the product in DCM at a concentration of 20% w/v, pour warm methanol into the solution (MeOH:DCM = 5:1 v/v) while stirring, and then put the flask in cold ice-water bath (still stirring) to precipitate the polymer and remove any unreacted monomers from the product. No lactide and much lower tin content would be detected in the thus purified product. If you would like to further reduce the tin content in the resulted polymer, you should dissolve a small amount of citric acid or another chelating agent in the non-solvent (MeOH) before precipitating the polymer. This reduced the tin content in my samples from 500 to 10 ppm (as indicated by AAS) which is highly desirable for pharmaceutical and biomedical applications.

The PEG-PLA copolymers are water white when melted and form white powder or fluffy precipitates, depending on molecular weight of both PEG segment and the final polymer, and polymer composition as well. However, when lactide is polymerized at higher temperatures, in the presence of high amounts of commercial, unpurified tin octoate, the reaction mixture often turns yellow or brown with a prolonged time. I would, therefore, suggest you modify the polymerization conditions for the synthesis of low molecular weight PLA (Mn < 5,000) as follows: lower temperature (130 deg C), shorter time (6 h) and lower SnOct content in feed ([LA]/[SnOct] = 2000 mol/mol).

n-Hexane as a non-solvent for the purification of PLA by the diss-pptn method is definitely a bad choice since unreacted lactide monomer does not dissolve readily in non-polar solvents and remains in the precipitated product.

PEG is soluble in many organic solvents except hexane.

Hi Gloria Kim,

Polyethylene glycols having a molecular weight of 1000 ,are soluble in many organic solvents, including aliphatic ketones and alcohols, chloroform, glycol ethers, esters,

and aromatic hydrocarbons; they are insoluble in ether and in most aliphatic hydrocarbons; with increased molecular weight, water solubility and solubility in organic solvents decrease

PEG is soluble in benzene, methanol and dichloromethane. you can use benzene to disslve PEG instead of chloroform. If not possoble, you may dissolve PEG in minimum amount of benzene and add chloroform to this solution slowly for homogeneous solution.

Check the CRC Handbook of Chemistry and Physics for a comprehensive table of solubility data (its listed in the "Physical properties of organic/inorganic compounds" tables). For safety's sake, do avoid use of highly toxic solvents such as benzene if at all possible; also, be careful if using a combination of chlorinated and non-chlorinated solvents to check that they are compatible.

It will dissolve well in chloroform if you heat it above its melting point.

I synthesis co-polymer poly(lactic acid-block-ethylene glycol). I employee PEG400 so that product is liquid. I want to isolate crude product by dissolving this mixed in chloroform and then precipitate by diethyl ether. I want to know that Can I collect purity co-polymer in that case? How to eliminate clearly unreacted lactide and unreacted PEG .? Conditions I play this course in 160 ( oC) . molar ratio of LD to PEG400 = 5 : 1 , and Sn(Oct)2 is 1% mol of hydroxyl group of PEG400 for 8 hrs

Khoa, try precipitating into MeOH.

thanks Justin Poelma

Does anybody know color of tri-block co-polymer PLA-PEG-PLA when it precipitated by MeOH ?

what ratio of solution includes n-Hexane with MEOH for precipitating co- polymer PLA-PEG-PLA ?

Khoa, before you go any further with your purification procedure, please keep in mind that the obtained triblock copolymer, synthesized under the given conditions, should have low molecular weight (Mn of ca. 2,400) and quite low glass transition temperature (below r.t.), in case of quantitative yield of the product. There is no information which lactide isomer you used. If L-lactide was used, the synthesized polymer would crystallize if precipitated, thus facilitating the purification by the dissolution-precipitation technique.

I have performed numerous syntheses of PEG-PLA copolymers with the use of all lactide isomers (L, D, rac, meso). I would recommend you dissolve the product in DCM at a concentration of 20% w/v, pour warm methanol into the solution (MeOH:DCM = 5:1 v/v) while stirring, and then put the flask in cold ice-water bath (still stirring) to precipitate the polymer and remove any unreacted monomers from the product. No lactide and much lower tin content would be detected in the thus purified product. If you would like to further reduce the tin content in the resulted polymer, you should dissolve a small amount of citric acid or another chelating agent in the non-solvent (MeOH) before precipitating the polymer. This reduced the tin content in my samples from 500 to 10 ppm (as indicated by AAS) which is highly desirable for pharmaceutical and biomedical applications.

The PEG-PLA copolymers are water white when melted and form white powder or fluffy precipitates, depending on molecular weight of both PEG segment and the final polymer, and polymer composition as well. However, when lactide is polymerized at higher temperatures, in the presence of high amounts of commercial, unpurified tin octoate, the reaction mixture often turns yellow or brown with a prolonged time. I would, therefore, suggest you modify the polymerization conditions for the synthesis of low molecular weight PLA (Mn < 5,000) as follows: lower temperature (130 deg C), shorter time (6 h) and lower SnOct content in feed ([LA]/[SnOct] = 2000 mol/mol).

n-Hexane as a non-solvent for the purification of PLA by the diss-pptn method is definitely a bad choice since unreacted lactide monomer does not dissolve readily in non-polar solvents and remains in the precipitated product.

I have just made a simple table in Excel 2010 for fast calculation of masses of reactants in ROP with predetermined variable parameters such as Mn and composition of the final polymer. I hope it can be useful to some of you.

I am attaching the file here as there is no possibility of enclosing files while sending a private message.

PEG should be soluble in chloroform.

Due to its high crystallinity, the dissolution of PEG (even in water) is a slow process. It is better to dissolve it whether in water or organic solvents at slightly elevated temperatures for a longer times with constant stirring. Otherwise, gellation takes place.

How do we calculate molar ratio of components in feed? What is "molar ratio in feed"?

PEG with M

Yes soluble, you can just warm for immediate solubility

I think most all common molecular weights are soluble in chloroform. For quickest dissolution, melt it and stir into the chloroform.

yes, it is

Hi Gloria

maybe it can help you:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4823654/