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    Unexpected conformational behavior of poly(poly(ethylene glycol) methacrylate)-poly(propylene carbonate)-poly(poly(ethylene glycol) methacrylate) (PPEGMA-PPC-PPEGMA) amphiphilic block copolymers in micellar solution and at the air-water interface

    Year: 2020

    Journal: J. Colloid Interface Sci., Volume 566, APR 15, page 304–315

    Authors: Lee, Jaewon; Pan, Jingyi; Chun, Jaehun; Won, You-Yeon

    Organizations: NSFNational Science Foundation (NSF) [CBET-1264336, IIP-1713953, CBET-1803968]; ACS PRFAmerican Chemical Society [602033-ND7]; Purdue University Center for Cancer Research (PCCR) via an NIH NCI grant [P30 CA023168]; DOE-BES/DMSE

    Keywords: Poly(poly(ethylene glycol) methacrylate) (PPEGMA); Poly(propylene carbonate) (PPC); Amphiphilic block copolymer; Micelle; Cryogenic transmission electron microscopy (cryo-TEM); Rheology; Langmuir monolayer; Surface pressure-area isotherm

    Hypothesis: This paper investigates the self-assembly behavior of a new amphiphilic block copolymer, PPEGMA-PPC-PPEGMA, in dilute aqueous solution and at the air-water interface. in PPEGMA-PPC-PPEGMA, the hydrophilic PEG moieties exist as side chains attached to the PMA backbone. Because of this unique non-linear architecture, the morphological and conformational properties of self-assembled PPEGMA-PPC-PPEGMA polymers are expected to be different from those of conventional linear PEG-based polymer surfactants. Experiments: For this study, three PPEGMA-PPC-PPEGMA samples having an identical PPC molecular weight (5.6 kDa) and different PPEGMA molecular weights (7.2, 2.8 and 2.1 kDa on either side) (named G7C6G7 G3C5G3, and G2C6G2, respectively) were synthesized. The micellar self-assembly behaviors of these materials were investigated by cryo-TEM, rheology, DLS, and visual observation. Langmuir monolayers of these materials were characterized by surface mechanical testing. Findings: PPEGMA-PPC-PPEGMA micelles were found to have a spherical geometry, irrespective of copolymer composition. Interestingly, G2C6G2 and G3C6G3 micelles formed weakly-bound clusters, whereas G7C6G7 micelles predominantly existed as isolated micelles. Detailed analysis suggests that this unexpected trend in micelle morphology originates from the fact that the PPEGMA blocks are only partially hydrated at aqueous interfaces. Detailed features of the surface pressure-area isotherms obtained from Langmuir PPEG-PPC-PPEGMA monolayers further supported this notion. (C) 2020 Elsevier Inc. All rights reserved.
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