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Crystallization behaviors and kinetics of iPP in an in-situ prepared isotactic polypropylene/graphene (iPP/G) composites were studied in this paper. In samples used in this study, the graphene fillers were well dispersed, and the interfacial adhesion exhibited enhanced features between graphene and iPP components. The thermal stability of the composites was improved by about 100 °C compared to the pristine iPP. It was found that the crystallization morphology, crystallization rate and kinetics of the iPP/G composites were significantly influenced by the presence of graphene. The nucleation and epitaxial growth of iPP on the graphene surface were observed and studied in detail. It was observed that the nucleation of iPP favored to occur at the wrinkles and edges due to the good match of the lattice parameters and the weak spatial hindrance compared to the smooth surface. Numerous nuclei epitaxially formed and the size of the crystals was very small. The schematic diagram was also proposed for the nucleation and growth process of iPP on the graphene surface in the iPP/G composites. Meanwhile, the overall crystallization kinetics and crystals growth were analyzed through Avrami equation. The obtained Avrami index n decreased with the graphene loadings and was close to 2 for the iPP/G composites, which implied that the growth of iPP in the composites was in two-dimension. And this was caused by the structure of graphene and the spatial confinement effect of graphene platelets in the iPP/G composites.

Morphological structure development of the in-situ polymerized isotactic polypropylene/graphene nanocomposites was investigated during the annealing process. The material was prepared via an in-situ slurry polymerization method with graphene-supported Ziegler–Natta catalyst. An interpenetrating network was observed at a relatively low graphene concentration after the sample was annealed for a long period (one to several hours). Alternative Conductivity impedance spectroscopic measurements showed a remarkable electrical conductivity increase of several orders of magnitude after the network was formed. At very low graphene content, although macroscopic network cannot be formed, the electrical conductivity can be enhanced through annealing as well. It implied that the rearrangement of the clusters or aggregates was necessary and such rearrangement favored the network formation. The network forming process was investigated through optical and electron microscopy methods and discussed based on the viscoelastic phase separation model. The effect of network on the crystallization behaviors was also investigated. It showed that the overall crystallization was improved by the presence of graphene platelets, but depressed after the network was formed, which was due to the spatial confinement and the decrease of total surface area available for heterogeneous nucleation.

In order to promote efficiency of the preparation of isotactic polypropylene (i-PP)/montmorillonite (MMT) nanocomposites by in situ polymerization technique, a strategy was laid out to enhance both the intercalative selectivity and the catalyst activity of the in situ polymerization by a combined use of a functional surfactant for MMT modification and a metallocene catalyst system for isospecific propylene polymerization. Thus, (2-hydroxylethyl) hexadecyl diethylammonium iodine was involved in the ion-exchanged organic modification of MMT, leading to an implantation of catalyst-anchoring reactive sites (hydroxyl, OH) in the interlayer galleries of MMT (OMMT). By treating the OH-intercalated OMMT successively with excessive methylaluminoxane (MAO) and rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2, the metallocene catalyst typical for i-PP polymerization was stabilized inside the interlayer galleries with a catalytically benign environment. The MMT-borne catalyst, upon further activation by MAO, released fairly high activities for propylene polymerization. The effective intercalative polymerization ensured an efficient preparation of i-PP/MMT nanocomposite. A series of i-PP/MMT nanocomposites containing completely disordered MMT at a loading range of 1.0–6.7 wt% (TGA measurement residue at 600 °C) were obtained in high yields.

This paper discusses a strategy of enhancing the structure stability of polyethylene/montmorillonite (PE/MMT) nanocomposites prepared by intercalative polymerization technique. The chemistry centers on an in situ, controlled PE matrix functionalization that is made possible by engaging a reactive comonomer in the intercalative polymerization process to intentionally anchor in the formed PE matrix ready-to-functionalize reactive groups. Thus, ethylene polymerization was conducted in the presence of p-methylstyrene (p-MS) using an OMMT (organically modified MMT)-intercalated metallocene catalyst (Et[Ind]2ZrCl2 in combination with MAO), resulting in p-MS-containing PE/OMMT nanocomposites. Subsequent functionalization of the PE matrix then facilely and selectively occurred on the benzyl group in the p-MS unit, including a free radical maleation reaction and a butyllithium-initiated metallation reaction which was followed by an anionic graft-from polymerization of methyl methacrylate (MMA), under very mild reaction conditions. The in situ-incorporated functional groups, including the pendant maleic anhydride groups and the polar poly(methyl methacrylate) (PMMA) side chains, significantly improved miscibility between the PE matrix and laminated silicate layers of MMT, leading to effective stabilization of the nanocomposite structure against processing.