Chain‐Scission‐Induced Intercalation as a Facile Route to Polymer Nanocomposites

Abstract

Polymer/clay nanocomposites (NCs) prepared using melt intercalation must be properly formulated and processed to achieve intercalation or exfoliation. Organically modified layered silicates (OMLSs) are often used to permit polymer intercalation and thereby separate the silicate platelets. Prior modeling efforts [1] suggest that high-molecular-weight (HMW) polymers tend to yield immiscible NCs unlike their low-molecular-weight (LMW) analogs, which commonly result in exfoliated or intercalated NCs. Although formulations containing LMW polar additives (e.g., maleic anhydride copolymers) have succeeded in producing at least partially exfoliated rather than immiscible NCs, [2][3][4] a need persists for simpler HMW formulations in order to expedite industrial scale-up. The present study examines blends composed of HMW polystyrene (PS) and an OMLS that remains largely immiscible when annealed under an inert N 2 atmosphere with little or no shear. Controlled thermal-oxidative chain scission of the HMW PS in an O 2 -rich environment promotes intercalation of short PS chains within the OMLS, thereby expanding and disordering the platelets as an intercalated NC develops. This scission-induced intercalation mechanism ensures that the resultant NC is in a thermodynamically stable state unlike NCs prepared using in situ polymerization, which may deintercalate during further processing. [5,6] Moreover, scission intercalation may be used as a general means by which to promote intercalation or possibly exfoliation in previously reported [4,7,8] immiscible NCs.Polymeric NCs containing clay have become an increasingly important topic in the development of lightweight, [9][10][11][12] tough, [13][14][15][16][17][18][19] and impermeable [18][19][20][21] materials since the Toyota research laboratories polymerized nylon-6 in the presence of sodium montmorillonite (Na-MMT) for automotive applications in the late 1980s. [22] In situ polymerization has enjoyed the most success in producing exfoliated NCs wherein individual clay platelets are uniformly dispersed in a polymeric matrix, because the polymer chains can grow within the silicate galleries. Another NC-fabrication strategy is solution intercalation, [23] in which polymer, solvent, and clay are mixed together. In this case, confinement of polymer chains upon diffusion into the silicate galleries is compensated for by the entropic gain caused by desorbed solvent molecules. Both in situ polymerization and solution intercalation typically require relatively large quantities of organic solvent, whereas melt intercalation [24] relies on annealing above the glass-transition (T g ) or melting (T m ) temperature of the polymer matrix under static or shear conditions. Melt intercalation constitutes an environmentally benign and commercially feasible process that successfully yields intercalated or exfoliated NCs from more polymer-clay pairs than either in situ polymerization or solution intercalation. Giannelis and co-workers [24][25][26] have previously demonstrated that sieved PS powder ...

Reduction of Graphite Oxide with a Grignard Reagent for Facile In Situ Preparation of Electrically Conductive Polyolefin/Graphene Nanocomposites

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Physical Chemistry of Intercalated System

“…[261] AIBN was introduced in organic-modified MMT, after which PS was intercalated from melt. Some increase in interplanar distance can be related with exothermal process of decomposition of the initiator and forming of free volume due to gas emission, which accelerates exfoliation [268]. Extrusion of a polymer with aggregated silicate (Fig.…”

Unusual rheological characteristics of polypropylene/organoclay nanocomposites in continuous cooling process

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