Surface modification using thiol-acrylate conjugate addition reactions

A novel method for forming surface-bound polymer films using amine-catalyzed thiol-acrylate reactions is investigated. The surface is modified with a thiol-terminated self-assembled monolayer (SAM) and treated with acrylate monomer in the presence of an amine catalyst. A conjugate addition reaction takes place at the surface, attaching an acrylate molecule to the surface. The fraction of attached acrylate on the surface was controlled by the reaction time, forming a gradient of acrylate surface density, and the acrylate fraction of the surface was changed from 0 to 0.6. An orthogonal gradient comprised of either the same acrylate functionality or multiple functionalities was also obtained on the same surface. The technique was further modified to yield acrylate surface density gradient on a polymer surface. Thicker films were grown in a controlled manner by polymerizing a dithiol-diacrylate mixture on a thiol-terminated surface, and the thicknesses of the films were controlled from 0.1 to 6 nm by changing the thiol-acrylate stoichiometry and the extent of reaction. In both cases the surface densities of the attached chains were theoretically calculated, and a model to predict them was proposed.