In situ polymerization

In polymer chemistry, in situ polymerization is a preparation method that occurs 'in the polymerization mixture' and is used to develop polymer nanocomposites from nanoparticles. There are numerous unstable oligomers (molecules) which must be synthesized in situ (i.e. in the reaction mixture but cannot be isolated on their own) for use in various processes. The in situ polymerization process consists of an initiation step followed by a series of polymerization steps, which results in the formation of a hybrid between polymer molecules and nanoparticles. Nanoparticles are initially spread out in a liquid monomer or a precursor of relatively low molecular weight. Upon the formation of a homogenous mixture, initiation of the polymerization reaction is carried out by addition of an adequate initiator, which is exposed to a source of heat, radiation, etc. After the polymerization mechanism is completed, a nanocomposite is produced, which consists of polymer molecules bound to nanoparticles. In polymer chemistry, in situ polymerization is a preparation method that occurs 'in the polymerization mixture' and is used to develop polymer nanocomposites from nanoparticles. There are numerous unstable oligomers (molecules) which must be synthesized in situ (i.e. in the reaction mixture but cannot be isolated on their own) for use in various processes. The in situ polymerization process consists of an initiation step followed by a series of polymerization steps, which results in the formation of a hybrid between polymer molecules and nanoparticles. Nanoparticles are initially spread out in a liquid monomer or a precursor of relatively low molecular weight. Upon the formation of a homogenous mixture, initiation of the polymerization reaction is carried out by addition of an adequate initiator, which is exposed to a source of heat, radiation, etc. After the polymerization mechanism is completed, a nanocomposite is produced, which consists of polymer molecules bound to nanoparticles. In order to perform the in situ polymerization of precursor polymer molecules to form a polymer nanocomposite, certain conditions must be fulfilled which include the use of low viscosity pre-polymers (typically less than 1 pascal), a short period of polymerization, the use of polymer with advantageous mechanical properties, and no formation of side products during the polymerization process. There are several advantages of the in situ polymerization process, which include the use of cost-effective materials, being easy to automate, and the ability to integrate with many other heating and curing methods. Some downsides of this preparation method, however, include limited availability of usable materials, a short time period to execute the polymerization process, and expensive equipment is required.    The next sections will cover the various examples of polymer nanocomposites produced using the in situ polymerization technique, and their real life applications.  Towards the end of the 20th century, Toyota Motor Corp devised the first commercial application of the clay-polyamide-6 nanocomposite, which was prepared via in situ polymerization. Once Toyota laid the groundwork for polymer layered silicate nanocomposites, extensive research in this particular area was conducted afterwards. Clay nanocomposites can experience a significant increase in strength, thermal stability, and ability to penetrate barriers upon addition of a minute portion of nanofiller into the polymer matrix. A standard technique to prepare clay nancomposites is in situ polymerization, which consists of intercalation of the monomer with the clay surface, followed by initiation by the functional group in the organic cation and then polymerization. A study by Zeng and Lee investigated the role of the initiator in the in situ polymerization process of clay nanocomposites. One of the major findings was that the more favorable nanocomposite product was produced with a more polar monomer and initiator. In situ polymerization is an important method of preparing polymer grafted nanotubes using carbon nanotubes. Due to their remarkable mechanical, thermal and electronic properties, including high conductivity, large surface area, and excellent thermal stability, carbon nanotubes (CNT) have been heavily studied since their discovery to develop various real world applications. Two particular applications that carbon nanotubes have made major contributions to include strengthening composites as filler material and energy production via thermally conductive composites.  Currently, the two principal types of carbon nanotubes are single walled nanotubes (SWNT) and multi-walled nanotubes (MWNT). In situ polymerization offers several advantages in the preparation of polymer grafted nanotubes compared to other methods. First and foremost, it allows polymer macromolecules to attach to CNT walls. Additionally, the resulting composite is miscible with most types of polymers. Unlike solution or melt processing, in situ polymerization can prepare insoluble and thermally unstable polymers. Lastly, in situ polymerization can achieve stronger covalent interactions between polymer and CNTs earlier in the process.