title: Spatial control over cross-linking dictates the pH-responsive behavior of poly(2-(tert-butylamino)ethyl methacrylate) brushes.
abstract: Surface-initiated atom transfer radical polymerization (ATRP) of 2-(tert-butylamino)ethyl methacrylate (TBAEMA) produced pH-responsive secondary amine-functionalized polymer brushes with dry thicknesses ranging from 4 to 28 nm, as determined by ellipsometry. At low pH, linear PTBAEMA brushes became protonated and highly swollen; brush collapse occurred when the solution pH was increased to ca. 7.7 due to deprotonation. PTBAEMA brushes were subsequently cross-linked using tolylene-2,4-diisocyanate-terminated poly(propylene glycol) (PPG-TGI) in either THF (a good solvent for PTBAEMA) or n-hexane (a poor solvent). The intensity of the C-C-O component (286.5 eV) in the C1s X-ray photoelectron spectrum increased after reaction with PPG-TDI, suggesting that cross-linking was successful in both solvents. Ellipsometry studies indicated that the pH-responsive behavior of these cross-linked brushes is dictated by the spatial location of the PPG-TDI cross-linker. Thus, uniformly cross-linked brushes prepared in THF became appreciably less swollen at a given (low) pH than surface-cross-linked brushes prepared in n-hexane. Micro- and nanopatterned PTBAEMA brushes were prepared via UV irradiation and interference lithography, respectively, and characterized by atomic force microscopy. The change in brush height was determined as a function of pH, and these AFM observations correlated closely with the ellipsometric studies.
authors.affiliation: Department of Chemistry, University of Sheffield , Brook Hill, Sheffield S3 7HF, United Kingdom.
authors.forename: Abdullah M
authors.initials: AM
authors.lastname: Alswieleh
authors.forename: Nan
authors.initials: N
authors.lastname: Cheng
authors.forename: Graham J
authors.initials: GJ
authors.lastname: Leggett
authors.forename: Steven P
authors.initials: SP
authors.lastname: Armes
mesh_terms: D003432:Cross-Linking Reagents / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008689:Methacrylates / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D008954:Models, Biological; D013499:Surface Properties
chemical_list: D003432:Cross-Linking Reagents; D008689:Methacrylates; C522816:poly(2-(tert-butylamino)ethyl methacrylate)