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We investigated the temperature-dependent structural evolution of thermoreversible triblock terpolypeptoid hydrogels, namely poly(N-allyl glycine)-b-poly(N-methyl glycine)-b-poly(N-decyl glycine) (AMD), using small-angle neutron scattering (SANS) with contrast matching in conjunction with X-ray scattering and cryogenic transmission electron microscopy (cryo-TEM) techniques. At room temperature, A100M101D10 triblock terpolypeptoids self-assemble into core-corona-type spherical micelles in aqueous solution. Upon heating above the critical gelation temperature (T gel), SANS analysis revealed the formation of a two-compartment hydrogel network comprising distinct micellar cores composed of dehydrated A blocks and hydrophobic D blocks. At T ≳ T gel, the temperature-dependent dehydration of A block further leads to the gradual rearrangement of both A and D domains, forming well-ordered micellar network at higher temperatures. For AMD polymers with either longer D block or shorter A block, such as A101M111D21 and A43M92D9, elongated nonspherical micelles with a crystalline D core were observed at T < T gel. Although these enlarged crystalline micelles still undergo a sharp sol-to-gel transition upon heating, the higher aggregation number of chains results in the immediate association of the micelles into ordered aggregates at the initial stage, followed by a disruption of the spatial ordering as the temperature further increases. On the other hand, fiber-like structures were also observed for AMD with longer A block, such as A153M127D10, due to the crystallization of A domains. This also influences the assembly pathway of the two-compartment network. Our findings emphasize the critical impact of initial micellar morphology on the structural evolution of AMD hydrogels during the sol-to-gel transition, providing valuable insights for the rational design of thermoresponsive hydrogels with tunable network structures at the nanometer scale.

Polypeptoids have recently emerged as a subject of scientificinterest due to their structural resemblance to existing pseudo-peptidicpolymers including poly(α-peptide)s, poly(β-peptide)s,poly(2-oxazoline)s, and poly(N-substituted acrylamide)s.With demonstrated backbone degradability, biocompatibility, and thermalprocessability, polypeptoids are potentially useful in a variety ofbiotechnological applications. Before those applications can be realized,it is important to develop their synthesis and understand their fundamentalproperties. In this Perspective, we will review recent advances inthe synthesis and characterization of polypeptoids and their copolymersas well as the development of polypeptoid-based functional and structuredmaterials. We will conclude by discussing the future prospects forthis nascent class of pseudo-peptidic polymers. [ABSTRACT FROM AUTHOR]