In situ polymerisation process

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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