Solution Evaporative Polymerization

A unique chemical polymerization technique for CP composites is solution evaporative polymerization. To cite an example, Han et al. [III.45] took a solution of FeCl3 (the oxidant) and PVA (the host polymer) in methanol, then added pyrrole monomer thereto. The oxidation potential of the solution, and hence the polymerization, could be changed and controlled via the proportion of FeClj to PVA as well as via evaporation of the solvent, and was optimally ca. +500 mV vs. SCE. Thus, simple casting of a film from this solution yielded P(Py) composite. The percolation threshold, for a saturation conductivity of ca. 10 S/cm, was claimed to be very sharp, at 5 w/w%. A method which appears to be a combination of solution evaporative polymerization and monomer-sorption polymerization is that carried out by Morita et al. [344] A P(Py)/PMMA composite, with nonhomogenous composition (a gradation of PMMA and P(Py) concentrations) was obtained in 0.1 to 10 pm thickness and 10 to 10 S/cm conductivity from combination of 2-butanone solutions of pyrrole, PMMA and benzoic acid with aqueous solutions of potassium persulfate. 

---

Table 2.4.2 presents a collection of contact resistance values measured for a few solution-deposited polymeric and oligomeric semiconductors. These values tend to be higher than in the case of evaporated oligomeric films due to lower mobilities. It has also been observed that, in certain instances, the source contact can constitute a majority of the total contact resistance in polymeric films [10,25]. 

Solutions of Polymeric Substances and Resins in Organic Solvents. A distinction is be drawn between adhesives that set by evaporation of the solvent and form an adhesive joint by adhesion of the dissolved polymer to the substrate surfaces, and adhesives for plastics, the solvent of which dissolves and swells the plastics surfaces and joins them by means of migration processes. This allows bonding of plastics that are otherwise difficult to join. The polymer solutes in solution adhesives act primarily as thickeners for establishing certain flow properties and retaining the solvent for the duration of the dissolution process. These solid components also may perform a limited gap-filling function. 

Masked exposure of a coating containing a polymeric binder, a polymerizable monomer and a photoactivated initiator can be used to make resist images. The coating can be prepared by solution evaporation or by lamination of a premanufactured film to a substrate. In the exposed areas the photolyzed initiator yields reactive species that initiate the polymerization of the monomer to form an interpenetrating network of the binder and the new polymer. The monomers that are used are... 

A third method to modify electrodes is the formation of a polymer layer at the surface of the electrode 22-24 The electrode is dipped into a solution containing the polymer and the solvent is evaporated. Polymerization of the monomer can also be induced at the electrode surface by electrochemical or other physical means. 

Continuous production of urea—formaldehyde resins has been described in many patents. In a typical example, urea and formaldehyde are combined and the solution pumped through a multistage unit. Temperature and pH are controlled at each stage to achieve the appropriate degree of polymerization. The product is then concentrated in a continuous evaporator to about 60—65% soflds (31). 

It is not always practical or convenient to investigate corrosion problems in the laboratory. In many instances, it is difficult to discover just what the conditions of service are and to reproduce them exactly. This is especially true with processes involving changes in the composition and other characteristics of the solutions as the process is carried out, as, for example, in evaporation, distihation, polymerization, sulfona-tion, or synthesis. 

---