Janus Hybramers: Self-Adapting Amphiphilic Hyperbranched Polymers

• Published in: Macromolecules Vol. 45; no. 5; pp. 2348 - 2358
• Main Authors: Samuel, Ashok Zachariah, Ramakrishnan, S
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 13.03.2012
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Polymers with particular properties; Preparation, kinetics, thermodynamics, mechanism and catalysts; Monolayer; 1,3-Dipolar cycloaddition; End group; Hydroxyester; Self condensation; Propargylic compound; Condensation polymerization; Air water interface; Ethylene oxide polymer; Supramolecular structure; Hyperbranched copolymer; Hydrophobic group; Molecular aggregation; Langmuir Blodgett layer; Amphiphilic polymer; Vesicle; Chemical solution; Thermal transition; Organic azide; Ester polymer; Surface topography; Branched copolymer; Ethylene oxide copolymer; Experimental study; Langmuir isotherm; Ester copolymer; Chemical modification; Preparation; Block copolymer
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma2022277

Janus structures have attracted a great deal of interest because of their fascinating properties and potential for applications. In this study, we demonstrate that hyperbranched polymers, bearing randomly placed docosyl (C22 alkyl segment) and PEG segments on their periphery, can readily reconfigure so as to segregate the alkyl and PEG segments, thereby generating Janus-type structures that we have termed Janus hybramers. DSC studies clearly reveal an endothermic transition that corresponds to the melting of the docosyl domains, while Langmuir isotherms demonstrate that these polymers form stable monolayers that appear to undergo a slight densification beyond a critical surface pressure; this suggested possible crystallization of the docosyl segments at the air–water interface. AFM studies of the transferred monolayers reveal various interesting aggregate morphologies at different surface pressures suggestive of island formation at the air–water interface; at the same time they also provided an estimate of the monolayer thickness. These Janus HBPs also form vesicles as evident from TEM and AFM studies; the AFM height of the deposited vesicles, as expected, was roughly 4 times that of the monolayer. SAXS studies revealed the formation of lamellar structures; the interlamellar spacing was largest when the relative mole fractions of docosyl and PEG segments were similar, but the spacing decreased when the mole fraction of either of these peripheral segments is substantially smaller; this suggested the possible presence of interdigitation within the domains of the minor component.