Semicrystalline crystallizes at the crystallization temperature from the melt state. But, this is true when the concentration is 100% like in the melt. What you did was to put this polymer in a solvent and the lower the concentration of the polymer. What happened in this case is to dissolve the amorphous portion first, and at the amorphous/crystalline interface, there is some disordered portion that is then dissolved in contact with the large amount of solvent, in part encouraged by the dissolving amorphous portion of the polymer chain. This process continues as the interface gradually propagetes into the deeper portion of the crystalline phase, eventually completely dissolving the crystalline region. This can happen at much lower temperature than crystallization temperature (even at room temperature) depending on the solubility property difference between the polymer and solvent (or the Flory-Huggins kai parameter) as well as the concentration of the polymer used.

@ Thank you, Dr. Ishida for your answer

Then can I think the opaque solution is because one of the block copolymer component is relatively insoluble to toluene?@

An opaque sample is usually the sign of phase separation with the domain size comparable or greater than the wavelength of the visible light. You should be able to see the phase separation via an optical microscope.

You can also calculate the solubility parameter of your copolymer (average the two structure for the time being) and toluene and if the separation is greater than 0.5, then chances are that you will have phase separation.

Dear all, I don't think you have a solution of this polar diblock copolymer in an apolar solvant which is toluene ! I think you have a dispersion. Other thing to consider is the possible self-assembly of this diblock copolymer in a 3D form such as micelles. If this is the case than opacity may be ecplained. My Regards

Abdelkader BOUAZIZ I thought PLLA is highly hydrophobic and PEO is also soluble in toluene due to its hydrocarbon chain

Dear all, I got details about the question from this site :

https://chemistry.stackexchange.com/questions/118925/how-can-i-explain-peo-b-pla-behaviors-in-dissolution

Anyway, both polymers show limited solubility in toluene mainly when MW's are high. The solubility is forced by increasing temperature and physical work. Again I am really convinced that this situation is due mainly to dispersion and/or self-assembly. This contribution is only an opinion. My Regards

Dear all, I think this reference help to a great deal to understand this question. My Regards

NB: please don't hesitate to tell me if you don't have Access to this paper.

Effects of various liquid organic solvents on solvent‐induced crystallization of amorphous poly(lactic acid) film

Shuichi Sato Daiki Gondo Takayuki Wada Shinji Kanehashi Kazukiyo Nagai

First published: 18 December 2012

https://doi.org/10.1002/app.38833

Dear Abdelkader BOUAZIZ , thank you for your answer.

As far as I understand, what you mean is each chain will be contracted in toluene and aggregated to form nanoparticles such as micelles? Do you think PEO should be the core?(It's tricky because solubility parameters are PLLA(20.2), PEO(20.8), and toluene(18.2).

Plus, I read some articles including the one you mentioned above, but some articles said toluene is good solvent for both PEO and PLLA(link below)Article Polymer brushes based on PLLA-b-PEO colloids for preparation...

Dear all, still a matter of contreversy to say good solvant, to what extent ? To tell you PEG and PEO are dehydrated by azeotropic distillation using BTX solvents' (benzene, toluene and xylene), at the end of the elimination of water the polymer precipitates upon cooling down.

If we take the solubility parameter for comparison, I would say yes PEO forms the core, but I am not sure that the value you mentionned are those or close to the MW's you are using. Solubility parameters are derived basing on the cohesive energy density (CED), which in turn is a function of chain length or MW.

I would rather prefer the information given in the paper I send, in which the influence of solvants on crystallization is the main reason, the partial solubility will be an additional factor which help the increased crystalization. My Regards

Dear Hosu Gwak,

Please see the attached document.

With my best regards

You have a polymer solution and can not discuss the polymer's melt/crystalline phase transition.