PMMA Nanocomposites Based on PMMA-Grafted α-Zirconium Phosphate Nanoplatelets

Dual-epoxide modification of α-zirconium phosphate (ZrP) nanoplatelets containing a bromine initiator was performed for surface-initiated activators regenerated by electron transfer atom transfer radical polymerization, resulting in poly(methyl methacrylate)-grafted ZrP (ZrP-g-PMMA) for dispersion in PMMA matrix. The morphology of the PMMA nanocomposites with variations in grafting density (σ) and grafted PMMA length (Ng) on ZrP-g-PMMA with a fixed PMMA matrix chain length (Nm) was investigated using transmission electron microscopy. Various types of polymer brush structures, including mushroom, semi-dilute polymer brush, and concentrated polymer brush structures, were prepared, which correspond to the wetting and dewetting phenomena of ZrP-g-PMMA in the PMMA matrices. The dual-epoxide functionalization helps decrease ZrP surface energy and improve the configurational entropy of grafted polymer chains, which results in the penetration of the matrix PMMA chains into the grafted brush layer at a low σ = 0.07 chain/nm2 even when Ng/Nm < 0.36. The rheological study in the melt state reveals that the flow properties of the PMMA nanocomposites can be tuned via changing the loading of nanoplatelets or varying the grafting characteristics at the interface between ZrP and PMMA matrix. Furthermore, the rheological behavior of PMMA/ZrP-g-PMMA which contains two-dimensional (2D) nanoplatelets was found to be significantly different from that of the PMMA/silica-g-PMMA which contains spherical nanoparticles. This drastic discrepancy in their rheological behaviors is likely caused by the anisotropic nature of the 2D nanoplatelets in PMMA. The implication of the present study on the preparation of thermoplastic nanocomposites containing 2D nanoplatelets is discussed.