Observation of Bimodal LLDPE/TiO₂ Nanocomposites Produced by in Situ Polymerization with Zirconocene/MMAO Catalysts via Ga Modification on TiO₂ Nanofiller

Abstract

Nano-TiO₂ and its modification with gallium (nano-TiO₂-Ga) and zirconium (nano-TiO₂-Zr) were used here as nanofillers in production of linear low-density polyethylene (LLDPE). The nanoparticles were immobilized by modified-methyl aluminoxane (MMAO) to be a catalytic filler prior to introducing into the in situ polymerization of ethylene and 1-hexene using zirconocene catalyst, and consequently produced LLDPE/TiO₂ nanocomposites. It was found that the modified nano-TiO₂ by Ga and Zr can hold more amount of MMAO on the surface than the unmodified one. This is because the modified particles have a stronger interaction between MMAO and the surface, as observed by thermal gravimetric analysis (TGA). However, the stronger interaction leads to lower catalytic activities for the polymerization systems. Observing from the molecular weight distribution (MWD) of the resulting products, it was found that the modified nano-TiO₂ with Ga can produce the LLDPE/TiO₂ nanocomposites with bimodal MWD. This result was due to the heterogeneity of the surface after modification, which can generate the multiple active sites for the catalyst, leading to multimodal properties for the polymer.