Polymer Grafted Nanoparticles for Materials Design*

Over the past 15 years, the application of controlled radical polymerization techniques to grafted polymer chains has enhanced our ability to design the critical interface between inorganic particles and polymer matrices.  These interfaces can be prepared with control over many molecular variables such as chain density, chain length, polydispersity, chain architecture (e.g., block, gradient), end group chemistry, etc. In addition, interfaces can be created to contain multiple functionalities.  We have used the RAFT (reversible addition-fragmentation chain transfer) polymerization method with polymer grafting techniques as an approach to modify the surfaces of nanoparticles with a variety of functional polymers. We developed multiple approaches for attaching RAFT agents to the surface of nanoparticles with graft densities ranging from 0.01 to 0.8 chains/nm². Using these surface-immobilized RAFT agents, many monomers can be polymerized on the nanoparticle surfaces via surface-initiated RAFT polymerization in a controlled manner. However, this diversity of design strategies is not limited to a single population of chains. Another set of RAFT agents can be attached to the remaining free surface and a second (or third) population of polymer chains can be polymerized from the surface of the same particles.  This subsequent set of chains can possess a completely independent set of molecular variables (chain density, molecular weight, chemistry, architecture, etc.) from the initial population of grafted chains.   Thus, an almost limitless design space is available to create highly specified interfaces on nanoparticles. This presentation will provide an overview of the chemistry used to prepare multimodal polymer-grafted nanoparticles with precise control over multiple polymer chain variables, and examples in select applications.