Synthesis of silica-polymer hybrids by combination of RAFT polymerization and azide-alkyne cycloaddition 'click' reactions

An original strategy is presented to synthesize highly pure multiblock copolymers (up to tetrablock) of various monomers tethered to silica particles, by combining RAFT polymerization and click chemistry. Two approaches were compared that follow this strategy. In a first approach, Z-azide-functionalized polymers were prepared via a RAFT process and then tethered to silica particles via a direct click reaction. This approach led to well-defined grafted polymers with polydispersity indices lower than their as-prepared precursors, due to lack of dead chains. In a second approach, a one-pot method was employed, using clickable RAFT agents to perform RAFT polymerization and click reaction simultaneously. This route afforded grafted polymers with polydispersity typically less than 1.25, whilst the chain length of grafted polymers was usually shorter than that of free polymers formed in solution, due to shielding effect and heterogeneous reaction condition. A series of well-defined homopolymers, di-, tri- and tetrablock copolymers could be efficiently grafted onto silica particles, and the grafting density was usually ranged between 0.017 and 0.085 chains nm(-2), evident from GPC, IR, elemental and thermogravimetric analyses. The one-pot approach seems more promising than the incremental route, since it is a one step reaction that still maintains controllability over surface modification.