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

Jaewon Lee; Jingyi Pan; Jaehun Chun; You-Yeon Won

doi:10.1016/j.jcis.2020.01.080

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

J Colloid Interface Sci. 2020 Apr 15:566:304-315. doi: 10.1016/j.jcis.2020.01.080. Epub 2020 Jan 24.

Authors

Jaewon Lee¹, Jingyi Pan², Jaehun Chun³, You-Yeon Won⁴

Affiliations

¹ Department of Biomedical, Biological and Chemical Engineering, University of Missouri, Columbia, MO 65211, USA.
² Davidson School of Chemical Engineering, Purdue University, West Lafayette, IN 47907, USA.
³ Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99352, USA.
⁴ Davidson School of Chemical Engineering, Purdue University, West Lafayette, IN 47907, USA. Electronic address: yywon@ecn.purdue.edu.

PMID: 32007741
DOI: 10.1016/j.jcis.2020.01.080

Abstract

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.

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