Design Strategies for Janus and Core–Shell Structures and Single- Ion Conducting Membranes Based on Hyperbranched Polymers

Abstract

Hyperbranched polymers (HBPs) are a class of highly branched macromolecules characterized by their low melt viscosity, high solubility, and numerous terminal functional groups amenable to chemical modification.1 Janus polymeric architectures, which feature distinct chemically incompatible domains within a single macromolecular framework, have attracted significant interest due to their unique self-assembly behavior and have been prepared using different strategies, most of which involve multi-chain aggregated systems; single chain Janus polymeric systems are relatively rare and hold the potential to reveal several interesting properties. Previous studies showed that simultaneous co-clicking of two immiscible segments, such as PEG and long alkyl chains, on to the periphery of hyperbranched polymers (HBP) can lead to self-segregation of the segments in bulk to generate Janus structures, thereby leads to the formation of bilayer lamellar ordering.2 AB2 type monomers carry one equivalent excess of B-groups, and hence can undergo direct copolymerization with any molecule carrying a single A-group; likewise, if two different molecules, carrying a single A-group each, are taken, it would lead to the formation of a HBP carrying two types of segments on their periphery. This concept has been utilized to develop Janus HBPs in a one-step process. Specifically, we have copolymerised 5-(ω-hydroxyalkoxy) isophthalate (AB2) along with various n-alkanols (A-R) and polyethylene glycol monomethyl ethers (MPEG-350) (A-R'), under melt transesterification conditions.3 The resulting functionalized HBPs exhibited self-segregation of alkyl and PEG segments, as confirmed by differential scanning calorimetry (DSC) and X-ray scattering analyses. This direct approach to the preparation of Janus HBPs should render them readily scalable and therefore could find potential applications as emulsifiers, compatibilizers, multi-functional surfactants, etc. An alternative approach involved the use of orthogonally clickable HB copolyesters bearing allyl and propargyl esters. Sequential functionalization via azide-alkyne andthiol-ene click reactions with immiscible segments led to enhanced self-segregation. This strategy prevents hetero-functionalized termini, improving conformational reorganization and offering the potential for selective metal ion incorporation on either side of the Janus structure. Additionally, amphiphilic core–shell structures were constructed by clicking oligo(ethylene glycol) (OEG) chains onto peripherally clickable HB polyesters.4 These materials exhibited lower critical solution temperature (LCST) behavior in water. Systematic investigations examined the effects of OEG chain length, grafting density, and linker chemistry on thermal responsiveness. To gain deeper insight into the impact of topology, linear analogues containing the same OEG pendants were also synthesised. Comparative analysis revealed that hyperbranched architectures consistently exhibited higher LCST values than their linear counterparts, underscoring the influence of branched topology and peripheral segment distribution on thermo-responsive behaviour. In last part, I discussed about the development of single-ion conducting solid polymer electrolytes based on Clickable Hyperbranched Polymer (HBP) scaffolds. Solid polymer electrolytes (SPEs) offer safer alternatives to liquid electrolytes in batteries; however, their practical implementation is limited by low ionic conductivity at room temperature. Solid membranes has been prepared through azide-alkyne click reaction, incorporating polyethylene oxide (PEO) as the ion-conducting segment and azide-terminated lithium trifluoromethanesulfonylamide as the lithium-ion source.5 The peripheral propargyl ester groups on the HBPs provide numerous sites for structural tuning. Since ionic transport in SPEs is closely associated with polymer chain mobility, varying the PEO-to-lithium salt ratio was used to modulate the amorphous character and optimize conductivity. Furthermore, crosslink density was tuned by adjusting the feed ratio of diazide-terminated PEO to monoazide PEO, enabling further control over the membrane properties