Using atom transfer radical polymerization to amplify monolayers of initiators patterned by microcontact printing into polymer brushes for pattern transfer

We report the use of atom transfer radical polymerization (ATRP) to amplify initiators patterned on films of gold into polymer brushes of poly(methyl methacrylate) (PMMA), poly(hydroxyethyl methacrylate) (PHEMMA), poly(tert-b utyl methacrylate) (PTBA), poly(isobornyl methacrylate) (PIBMA), and poly(( dimethylamino)ethylmethyl acrylate) (PDMAEMA). Pattern transfer into gold s ubstrates underlying polymer brushes was achieved by using the patterned br ushes as barriers to wet chemical etchants of gold. The surface-confined in itiators for ATRP were prepared by the self-assembly of (BrC-(CH3)(2)COO(CH 2)(10)S)(2) (I) on films of gold. These monolayers were assembled from solu tions of hexadecane at 60 degrees C so as to prevent their thermal desorpti on during ATRP (also performed at 60 degrees C). By measuring the resistanc e offered by these brushes to etching of underlying films of gold by aqueou s solutions of KI/I-2, KCN/K3Fe(CN)(6), and 50 vol % aqua regia (70 vol % H NO3 and 30 vol % HCl), we conclude that both the thickness and chemical fun ctionality of the polymer brushes as well as the choice of etchant can be t ailored to control the etch resistance of polymer brushes. Thick brushes fo rmed from hydrophobic monomers were found to be the most effective in resis ting all etchants. The etch resistance of a PMMA brush was observed to be g reatest when using aqua regia or KI/I2 to etch an underlying film of gold. For example, when using PMMA brushes (thickness 450 Angstrom), we measured the brushes to slow the etching of the underlying films of gold by KI/I-2 b y almost 2 orders of magnitude as compared to monolayers formed from I. By using microcontact printing to pattern SAMs formed from I, we demonstrate t he usefulness of ATRP in schemes for transferring patterns present in monol ayers of molecules into underlying substrates.