title: Exploring quality in gradient copolymers.
abstract: Quality of gradient copolymers is evaluated by atomic force microscopy (AFM) and correlated with molecular weight distribution (MWD) values. ARGET ATRP is employed with decreasing levels of catalyst concentrations to generate copolymers with increasing M¯w/M¯n values. The copolymers are transformed into molecular bottlebrushes to enable imaging and analysis of individual molecules by AFM. The average height (cross-sectional) profile of all bottlebrushes agrees with the instantaneous composition (ICHEMA-TMS ) of the analogous copolymer backbone, as determined by (1) H NMR. The copolymer synthesized with 500 ppm of catalyst exhibits more narrow distributions of both brush height and backbone length when analyzed as a bottlebrush by AFM. Correspondingly, the copolymers synthesized with lower catalyst concentrations yield bottlebrushes with broader height and length distribution. These results establish MWD values as an excellent trait to assess quality within gradient copolymers.
authors.affiliation: Center for Macromolecular Engineering, Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA, 15213, USA.
authors.forename: Andrea M
authors.initials: AM
authors.lastname: Elsen
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA.
authors.forename: Yuanchao
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA.
authors.forename: Qiaoxi
authors.initials: Q
authors.lastname: Li
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA.
authors.forename: Sergei S
authors.initials: SS
authors.lastname: Sheiko
authors.affiliation: Center for Macromolecular Engineering, Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA, 15213, USA.
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Matyjaszewski
mesh_terms: D009682:Magnetic Resonance Spectroscopy; D018625:Microscopy, Atomic Force; D008970:Molecular Weight; D011108:Polymers / Q000737:chemistry*
chemical_list: D011108:Polymers
keywords: activators regenerated by electron transfer (ARGET); atom transfer radical polymerization (ATRP); gradient copolymer; gradient deviation; molecular weight distribution