Surface modification using thiol-ene and thiol-acrylate polymerizations.

摘要

Thiol-ene and thiol-acrylate polymerizations have been investigated extensively in recent years due to their advantageous polymer properties. Thiol-ene photopolymerizations are radical-mediated step growth polymerizations, where a thiol molecule adds across the carbon-carbon double bond of an ene molecule upon exposure to UV light and radical generation. Thiol-acrylate conjugate addition reactions are base-catalyzed addition reactions where the thiol molecule reacts and adds across the acrylate carbon-carbon double bond. Both of these reactions follow a step growth mechanism and hence the stoichiometry and the functionality of the monomers is useful for controlling the final polymer structure and properties. In addition, these reactions are rapid, insensitive to oxygen, result in lower shrinkage and shrinkage stress and present a wide chemical versatility in the polymerizable monomers. As a result of these advantages, both polymerization schemes have been utilized for various applications.;In this project, surface modification using both thiol-ene photopolymerization and thiol-acrylate conjugate addition reactions was investigated. Various surface polymer film properties were controlled by changing the monomer formulations, polymerization conditions and the properties of the anchoring self-assembled layers. Each of these factors was changed individually or in conjunction with each other to control the film properties such as chemistry, thickness, chain length and density, hydrophobicity and patternable spatial resolution. Uniform, lithographically patterned as well as gradient polymer films, were deposited using both thiol-ene photopolymerizations and thiol-acrylate conjugate addition reactions.;To investigate the formation mechanisms of the formed films, the grafted polymer chains were cleaved from the surface and analyzed. The photopolymerized films were cleaved using acid hydrolysis of the ester groups and the conjugate addition thiol-acrylate films were cleaved using a photocleavable anchoring group. Both sets of grafted polymers were analyzed and compared with the non-bonded polymer, which was formed during the reaction but remained unattached to the surface. The influence of the monomer stoichiometry and the polymerization mechanism on the molecular weight of the grafted polymer and the surface chain density was studied.;The advantageous characteristics of the formed films were utilized to apply them for two broad applications. The thiol-acrylate conjugate addition reactions were used for modifying surfaces with biological peptides and properties such as the density and arrangement of the peptides were controlled. These peptide-modified surfaces were used to investigate cell-surface interactions. Thiol-ene photopolymerizations were utilized as a material for nanoimprint lithography to form functionalized, nanopatterned polymer surfaces. These nanopatterned surfaces were further modified with linear and crosslinked polymer films. The secondary, crosslinked polymer film was further micropatterned using traditional photolithographic techniques to obtain a multi-layered, nanopatterned polymer structure.