In Situ Polymerisation Processing

Initially, in situ radical polymerisation was applied for the synthesis of PMMA-MWNT composites by Jia et al. In this work, in situ polymerisation was performed using the radical initiator 2,2 -a2 obisisobutyronitrile (AIBN). The authors believed that n-bonds in CNTs were initiated by AIBN and therefore nanotubes could participate in PMMA polymerisation to form a strong interface between the MWNTs and the PMMA matrix. Then, Velasco-Santos et al. and Putz et al. also used AIBN as an initiator of in situ radical 

In situ epoxidation reaction has also been used for the preparation and processing of epoxy polymer composites. For instance, carboxyl- and fluorine-functionalised SWNTs have been integrated into an epoxy polymer via the 

In situ polymerisation reactions have also been applied to the preparation of other polymer-nanotube composites. For example, Kumar et al have synthesised new ultra-strong PBO composites in the presence of SWNTs in poly(phosphoric acid) (PPA) by in situ PBO polymerisation. After the polymerisation, PBO-SWNT composite fibres have been spun from the liquid crystalline solutions using dry-jet spinning. 

In general, in situ polymerisation can be used for the preparation of almost any polymer composites containing CNTs which can be non-covalently or covalently bound to the polymer matrix, as discussed above. 

PFT also involves in situ co-polymerisation of olefins catalysed directly from nanotubes pre-treated by a methylaluminoxane (MAO) or highly active metallocene-based complexes e.g. Cp2ZrCl2). This approach destroys nanotube bundles and results in homogeneously coated CNTs. 

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A closely related method to the in situ polymerisation processing of composites is based on epoxy resins thermosets. In this approach, CNTs can be dispersed in a liquid epoxy precursor and then the mixtures can be cured by the addition of hardener, such as triethylene tetramine (TETA), and the application of temperature or pressure. In most cases, the epoxy monomer exists in liquid state, facilitating nanotube dispersion. Curing is then carried out to... 

It should be mentioned that nucleation of crystallinity in the presence of nanotubes may occur in solution casting, melt processing and in situ polymerisation processing of some polymer-nanotube composites. 

Fig. 6. Flow diagram of microencapsulation process that utilises acid-cataly2ed in situ polymerisation of melamine or urea with formaldehyde to form a...

The in situ polymerisation consists of filling a capillary or a column with the prepolymerisation mixture containing the template, the functional monomer, the crosslinker, the initiator and the porogenic solvent (Fig. 11). Then the column is heated or submitted to UV radiation for polymerisation. In the in situ thermally initiated polymerisation process, the tube with the pre-polymerisation mixture is submerged in a controlled-temperature water bath, whereas for in situ photoinitiated polymerisation, a UV-transparent capillary or column is needed. The resulting continuous rod of polymer is washed with an appropriate solvent to remove the template and the excess of monomer. 

It is also possible to prepare chiral PANI by in situ polymerisation with CSA, and in this case the reaction can afford chiral nanotubes [63]. The optically active materials contain nanotubes with 80 to 200 nm outer diameter and an internal diameter of between 20 and 40 nm, as revealed through microscopy images. A self-assembly process was proposed in which anilinium cations and CSA anions form micelles which act as templates for the growing polymer chains. Nanotubes are also formed when (R)- or (S)-2-pyrrolidone-... 

In addition to traditional methods of influencing the catalytic activity and stereospecificity of Ziegler-Natta catalysts in butadiene polymerisation processes in situ and separate preparation, addition of modifiers, and so on), there is an... 

Usually, chemical reactions do not occur during these processing steps, exeept during the vulcanisation of rubber, during the in-process cross-linking of certain types of cable insulations made from polyethylene and when processing certain resins with in-situ polymerisations. Such special processing steps are described in literature [14, Winnacker-Kuechler, 1982]. 

Intercalated nanocomposites are usually formed by mixing in the melt or in situ polymerisation whereas exfoliation may require more complex processing depending on the properties of the clay (Usuki et al, 1993). However, such layered silicate-based polymer nanocomposites have attracted considerable recent interest after the commercialisation of polypropylene-and nylon-6-based materials (Krishnamoorti and Yurekli, 2001, Kiersnowski and Piglowski, 2004). The major barrier to commercialisation has been developing techniques to ensure a reliable and reproducible product which has now been addressed for clay-based composites some thirty or so years after they were first developed. 

The TPD spectra show an increase of the acidity due to the intercalation of Zr, except when the "ex-situ polymerisation" process is run at pH 3.9. In this latter case, the clay calcined either at 400 or 600 C presents almost the same total acidity as the Na-montmorillonite, even if the Zr02 content of the clay is very high. Different hypothesis may explain the increase of acidity of the three other samples. This may be due either to the presence of the pillars, to the accessibility of the internal surface, or to the junction between the pillars and the silica layers. Without additional experiments the comparison of the acidity and acid strength of mixed oxides, studied by Shibata et al. (14) with this system supports the last hypothesis. 

A third type of suspension is that in which polymer particles are suspended in monomer which is then polymerised. This is, however, rather more a variant of the casting process in which monomer or low molecular weight polymer is cast into a mould and then polymerised in situ. 

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