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Synergism among Polydispersed Amphiphilic Block Copolymers Leading to Spontaneous Physical Hydrogelation upon Heating

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journal contribution
posted on 04.09.2020, 17:13 by Shuquan Cui, Liang Chen, Lin Yu, Jiandong Ding
Molecular weight distribution (MWD) is an intrinsic character of synthetic polymers and influences many properties of polymeric materials. In this work, the effects of MWD on thermogelation of an amphiphilic block copolymer in water were studied mainly by a dynamic Monte Carlo simulation. Molar mass dispersity M, defined as weight-average molecular weight Mw over number-average molecular weight Mn, was found to be a key molecular parameter to influence the existence of sol–gel transition or the phase transition temperature if gellable. We also demonstrated that such a M effect in a selective solvent was closely related to the formation of micelles, particularly to the thickness of micellar corona. We revealed that the thermogelation of the polydispersed macromolecules resulted from the synergism among chains of different lengths leading to a percolated network of semibald micelles. The effect of M of hydrophobic blocks and that of hydrophilic blocks on thermogelation were compared and analyzed. By combining the simulation results with the previous experimental results about triblock copolymer PLGA–PEG–PLGA in water [PEG: poly­(ethylene glycol); PLGA: poly­(lactide-co-glycolide)], we proposed a MMw diagram for design of the thermogellable copolymers. This mechanism study deepens the understanding of thermogels and is helpful for guiding the molecular engineering of such a kind of soft matter in biomedical fields as an injectable hydrogel.