Functionalization of a Nano-Faujasite Zeolite with PEG-Grafted PMA Tethers Using Atom Transfer Radical Polymerization

Abstract

We report the controlled growth of poly(ethylene glycol) methyl ether grafted polymethacrylate (PEGPMA) on nanosized zeolite external surfaces using the atom transfer radical polymerization (ATRP) approach. As-synthesized amino-modified faujasite zeolite nanoparticles (40 nm) were reacted with 2-bromoisobutyryl bromide to covalently bond bromine onto the zeolitic surfaces. The bromine atoms then serve as initiators for ATRP, allowing growth of a variety of polymer tethers onto the nanozeolite surfaces. The PEGPMA polymer has a unique structure in which very flexible PEO oligomers are bonded to stiff polymethacrylate backbones. This structure makes it possible to synthesize nanohybrid materials with a fully amorphous polymer phase, a main requirement for conductivity of solid polymer electrolytes. Raman spectroscopy and 13C solid-state NMR spectroscopy were used to characterize the as-synthesized samples. Furthermore, both Raman spectroscopy and polymer molecular weight determinations demonstrated the controlled growth of polymer chains in the ATRP synthesis. DSC experiments indicated that a fully amorphous polymer phase can be achieved by properly controlling the polymerization conditions. The morphology of the polymer phase in PEGPMA−nanoNaX composites is very stable. DSC cycling scans in the temperature range −150 to 100 °C did not induce crystallization of the amorphous polymer segments. TEM images demonstrate significant variation of the zeolite surface properties after modification with polymer tethers, indicating that very dense hybrid zeolite-based thin films or membranes could be achieved using simple solvent-cast spin-coating techniques.