Composites of linear low-density polyethylene were obtained in toluene slurry by in situ copolymerization of ethylene and 1-octene in the presence of untreated magnesium oxide-hydroxide nanoparticles (MgO@Mg(OH) 2 ) of ±50 nm and such treated with dibutylmagnesium (DBM) as support for a bis(n-butylcyclopentadienyl)zirconium dichloride-methylaluminoxane (MAO) catalyst system. Treatment of the nanoparticles with DBM (0.5-6 mmol g −1 MgO@Mg(OH) 2 ) allows one to decrease the amount of MAO by 1.2 mmol Al g −1 MgO@Mg(OH) 2 , while reaching the same average catalyst activity and a finer distribution of the particles. Energy-dispersive X-ray mapping shows that the MAO is mainly associated with the filler. The crystallinity of the matrix polymer decreases with filler content.

Nanocomposites of isotactic polypropylene (iPP) with 0.5 wt% filler of MgO@Mg(OH)2 (35 nm) or silicon dioxide (20–60 nm) or barium titanate (50 nm) nanoparticles were obtained from melt compounding of filler masterbatches with commercial iPP. The masterbatches with 5 wt% nanofiller were prepared in an in situ polymerization procedure using a metallocene/methylaluminoxane (MAO) catalyst system that was supported on the respective oxides. The original agglomerates of the nanoparticles were broken up by treatment with dibutylmagnesium for MgO@Mg(OH)2, and with ultrasound in the presence of MAO for SiO2 and BaTiO3. The tacticity (98% mmmm) of the in situ formed PP was not influenced by the presence of the nanofillers. Scanning electron microscopy and energy‐dispersive X‐ray spectroscopy mapping show a fine dispersion of single particles and small clouds or clusters. The primary nanoparticles appear to be surrounded by polymer. The elongation at break was decreased to 50, 17 and 9% for MgO@Mg(OH)2), SiO2 and BaTiO3, respectively. After melt compounding with iPP, a homogeneous single‐particle distribution of the oxidic nanoparticles was found in the resulting composites with 0.5 wt% filler content. © 2019 Society of Chemical Industry