Functional polymer synthesis and efficient polymer modification via specific and orthogonal methodologies
Responsive polymeric materials can be prepared by a wide variety of synthetic techniques, though not all of these methods are widely applicable. We seek to develop routes to complex polymers by using only simple and straightforward chemical transformations. For instance, copper-catalyzed azide-alkyne coupling and other efficient synthetic strategies (Diels-Alder reactions, Michael addition, etc.) can be used to prepare, for example, functional telechelics, molecular bottle-brush copolymers, and thermoresponsive hyperbranches. We have developed new azido-functionalized chain transfer agents that allow end-functional polymers to be prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization. In addition to have controlled molecular weights, the resulting polymers contain azido groups capable of quantitatively reacting with small molecule or polymeric alkynes under non-demanding conditions. We also investigate end group transformations that exploit the telechelic sulfur functionality inherent to polymers prepared by RAFT. We have demonstrated that dithioester or trithiocarbonate end groups can be readily reduced to thiols capable of efficiently reacting with electron deficient alkenes to yield a range of materials, including modular block copolymers, functionalized surfaces, or polymer-protein conjugates. Many of the synthetic methods we consider fall within the realm of "click chemistry," and have proven to be excellent candidates for materials derivatization.