Reversible addition-fragmentation chain transfer (RAFT) polymerization has been widely used for the synthesis of varying polymer architectures, including polymer brushes on nanoparticles for incorporation into polymer nanocomposites. Surface modification via RAFT allows for control of the surface properties and therefore the interface between the nanoparticle and polymer matrix. Adverse interactions between the nanoparticles, grafted polymer, and polymer matrix can lead to aggregation and autophobic de-wetting. This can be suppressed while the entropic and enthalpic effects are decoupled for their independent study, using a bimodal system containing a small number of long, matrix compatible chains on a surface that primarily consists of a short dense brush. RAFT allows for the control of brush parameters such as composition, graft density, and molecular weight for both populations separately and independently. Bimodal brush grafted silica nanoparticles show superior dispersion and thermomechanical properties over monomodal brush grafted particles in polymer nanocomposites. Furthermore with a mixed bimodal system, short brushes offer an added enhancement in properties while keeping nanoparticles dispersed, as the long brushes remain matrix compatible for entanglement. Analogous to block copolymers, the addition of a polymer chain population with different chemical composition can lead to materials with added and differing properties compared to a bimodal system with a single chemical composition. The synthesis of these bimodal systems via grafting-from and grafting-to methods will be discussed as well as the above-mentioned enhancement in properties.

Properties and synthesis of mixed bimodal nanoparticles via RAFT

249th National Meeting (2015)

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