Self‐assembly and sol‐to‐gel transition of thermosensitive methoxy‐polyethylene glycol‐polyalanine block copolymer hydrogels.

Certain amphiphilic polymers can self‐assemble to form various structures, such as micelles and hydrogels in aqueous medium, depending on the concentration or temperature. These different structures have found many applications in biomedical and material processing fields. The assembly processes of the polypeptide‐containing diblock copolymer, methoxy poly(ethylene glycol)‐block‐poly(L‐alanine) (mPEG‐PA), was studied to elucidate the relationship between different structures with parameters such as chain lengths (volume fraction) of the two blocks, molecular weights, medium polarity, temperature, and concentration. Gelation mechanism was especially focused in the study. Various solution‐cast morphologies observed by scanning electron microscopy (SEM) imaging including cylinders and micelles aggregates can be obtained by using solvents with different polarity for casting with simply tuning the chain lengths. The sol‐to‐gel transition mechanism can be best explained by phase separation between polymer‐rich and water‐rich phases. It might be spinodal decomposition process to cause the phase separation. Furthermore, the branch and flack structures can be observed due to phase separation mechanism and different chain lengths by SEM images. This result offers new insights into behavior of mPEG‐PA system, enabling more controlled manipulation to various applications. [ABSTRACT FROM AUTHOR]