Selective Doping of Positive and Negative Spatial Defects into Polymer Gels by Tuning the Pregel Packing Conditions of Star Polymers

Abstract

Gels are giant single molecules that consist of a very large number (∼Avogadro's number) of cross-linked nanometer-size polymer chains. Unlike most low-molecular-weight compounds, the extensively crosslinked gel networks typically do not exhibit a well-defined structure. In a previous study, we disproved this preconception and demonstrated that by applying suitable percolation conditions during the gelation process, a highly homogeneous gel with an ordered structure can be synthesized. In the present study, we further demonstrate that by tuning the percolation conditions, stable polymer-rich or polymer-poor nanodefects can be selectively introduced in the gel network; the controlled addition of such nanodefects has not been achieved before. The successful introduction of nanodefects was confirmed using laser speckle tests, and their structures and dynamics were evaluated in Fourier space using static and dynamic scattering measurements. While the addition of polymer-rich defects had a relatively little effect on the elastic modulus of gels, the addition of pores significantly lowered the elastic modulus, suggesting that substantial topological defects were introduced simultaneously when the packing ratio was low. The controlled addition of such nanodefects may potentially modulate the structural, mechanical, optical, and mass transportation properties of the gels effectively, and thus serve as a new design strategy for gel materials.

Structure and Dynamics of Critical Polymer Clusters Formed with Tetra-Armed Star-Polymers

“…However, as diluting the polymer solutions, the relaxation time of the fast modes became slower, contrary to that of typical translational motion. The possible motion that satisfies the above experimental results is the concentration fluctuations, also known as cooperative diffusion, widely observed in semidilute polymer solutions [22][23][24][25] .…”

Hierarchy of relaxation times in supramolecular polymer model networks

“…Values in a very similar order of magnitude are also reported for non-ideal permanently connected tetra-PEG hydrogels. 28 Even though this transiently connected tetra-arm PEG-terpyridine gel is considered as a dynamic model system with its dissociating and re-associating polymer building blocks, static heterogeneities with density disparities are clearly present. The light scattering results are summarized in Table 1.…”

Characterization of N-phenylmaleimide-terminated poly(ethylene glycol)s and their application to a tetra-arm poly(ethylene glycol) gel

“…Tetra-arm poly(ethylene glycol) (TetraPEG) gels, which are constructed from TetraPEG with a reactive site at each of its termini, have extremely low heterogeneity and can be treated as near-ideal polymer networks. [24][25][26][27][28] TetraPEG gels exhibit high strength as well as high transparency due to their uniform mesh structure. In most cases, the network structures of TetraPEG gels are formed by combining mutually reactive TetraPEG prepolymers in solution, i.e., an AB-type coupling reaction between two TetraPEG prepolymers with reactive groups at each polymer end.…”

“…36 Therefore, novel AB-type coupling reactions are still required to expand the applications of gels based on the biocompatible polymer PEG with a uniform mesh structure. Furthermore, even though the fabrication and characterization of TetraPEG gels with a uniform mesh structure have been widely studied, 25,28,30,[37][38][39][40][41] little has been reported regarding the one-pot synthesis of tetra-arm precursors from commercially available polymers.…”