Grafting of polymers from clay nanoparticles via in situ free radical surface-initiated polymerization: Monocationic versus bicationic initiators

Surface-initiated polymerization (SIP) from clay nanoparticles was compared between surface-bound mono- and bicationic free radical initiators. Distinct properties in molecular weight (MW), extent of exfoliation, and particle morphology were observed as a consequence of using two different initiator architectures. X-ray diffraction (XRD) results showed that the clay intercalated with monocationic initiator has a larger d spacing and gave a more ordered structure. IR, X-ray photoelectron spectroscopy, and qualitative thermogravimetric analysis confirmed the attachment of both initiators. XRD further showed that the SIP product from the bicationic initiator retained some intercalated structure while a highly exfoliated structure is achieved by the SIP through the monocationic initiator. Consequently the monocationic initiator gave a higher MW polymer. We have found that well-dispersed intercalated clay particles and efficient monomer diffusion are crucial factors in performing a successful SIP and in achieving an exfoliated clay structure.