High density scaffolding of functional polymer brushes: surface initiated atom transfer radical polymerization of active esters.

In this Article, we describe a method for the polymerization of active esters based on N-hydroxysuccinimide 4-vinyl benzoate (NHS4VB) using surface initiated atom transfer radical polymerization (SI-ATRP). Poly(NHS4VB) brushes have high grafting density and a uniform and smooth morphology, and film thickness increases linearly with reaction time. Block copolymer brushes with 2-hydroxyethyl acrylate, tert-butyl acrylate, and styrene were synthesized from surface bound poly(NHS4VB) macroinitiators. The active ester brushes show rapid and quantitative conversion under aminolysis conditions with primary amines, which was studied using grazing incidence attenuated total reflection Fourier transform infrared (GATR-FTIR) and UV-vis spectroscopy. UV-vis was also used to quantify the amount of reactive groups in polymer brush layers of differing thickness. Functionalization of the active ester pendant groups with chromophores containing primary amines showed a linear correlation between the amount of chromophore incorporated into the brush layer and brush thickness. Grafting densities as high as 25.7 nmol/cm(2) were observed for a 50 nm brush. Block copolymer brushes with buried active ester functional moieties also undergo quantitative conversion with primary amines as confirmed by GATR-FTIR. We discuss the potential of activated ester brushes as universal scaffolds for sensor and microarray surfaces, where the twofold control of functionalizable active ester polymer and block copolymers provides well-ordered, tunable microenvironments.