Thiol-X Chemistries in Polymerization: Photopolymerization and Sequence Controlled Polymer Synthesis

Weixian Xi, University of Colorado Boulder


Thiol-X chemistries are representative group of click reactions that are based on the unique chemical property of thiol including radical initiated thiol-ene reaction, base or nucleophile catalyzed thiol-Michael addition, base-catalyzed thiol-isocynate reactions. All of these reactions have been widely employed in the polymer chemistry and materials science. In this thesis, two most common used thiol-X reactions (thiol-ene and thiol-Michael addition) are investigated and developed into photopolymerization and sequence controlled polymer synthesis.

Traditional thiol-Michael addition reaction is initiated by adding base or nucleophile. Since the fast kinetics of the reaction itself, it is usually difficult to have the spatial and temporal control of the reaction, which is critical in some materials fabrication. Light provides a precise tool to control the reaction when and where to occur. Thus, in this thesis, combination of photochemical process to generate catalysts for thiol-Michael addition enables photo control of the reaction and have been demonstrated to be used in photopatterning, two-stage polymer networks formation, which promote thiol-Michael addition into “photo-click” realm.

Sequence controlled polymers are defined as macromolecules whose monomer arrangements are in precise order. In traditional copolymers the distribution of monomers is usually uncontrolled or statistically controlled. In contrast, in natural polymers such as DNA and proteins, the primary sequence is precisely controlled where in DNA the order conveys genetic information while in proteins the order of the amino acids dictates both primary and secondary structure. Ultimately, in both instances, the sequences dictate the characteristics and function of the molecules. In the thesis, a strategy that combines “thiol-ene” and “thiol-Michael” addition click chemistries was developed to synthesize sequences controlled polymers. With nucleobases as sideschains for these polymers, these sequences are analogs of oligonucleotides in nature. The click nucleic acids (CNAs) synthesized here exhibited sequence specific interactions which were used in the directed self-assembly of nanoparticles, organogel formation, and surface-based biodetection.