Unique Chemical Polymerization Methods

An example of the use of the use of novel polymerization techniques is provided by the direct photosensitized polymerization of pyrrole by Ru(bpy)3 (Fig. 5-16) carried out using a 490 nm dye laser in a matrix of Nafion, which also served as the dopant [90]. 

Another unique polymerization mediod is embodied in the work recently described by Schafer et al. [97]. In this, P(PV) was prepared by chemical vapor deposition (CVD), specifically vapor phase pyrolisis of a,a( )-dihalogenated-p-xylenes. The targeted application was LEDs, and unusually high rectification ratios were observed in these. Fig. 5-17 shows a schematic of the polymerization apparatus and process. 

5-17 Schematic of apparatus and process for CVD polymerization of poly(phenylene vinylene). After Reference [97], reproduced with permission. 

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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. 

Anionic polymerization. For some heterocyclic monomers the unique chemical structure of the growing species follows unequivocally from the monomer structure. However, in many cases isomeric structures have to be taken into account. For instance, for symmetrical monomers, like thietane, the carbanion but not the thiolate anion was proposed (4). Unsymmetrically substituted monomers can provide active species by a- or B- ring scission. Unusual structure of activated monomer was proposed for NCA and lactams. These structures can not be distinguished by spectrophotometric methods, and application of H- or 13C-NMR looks more promising. 

The last method/722 is unique in that the activated species formed at an elevated temperature in the gas phase undergoes self-addition on the cold substrate surface to produce the precursor polymer that can be subjected to thermolysis to the final polymer. This method does not require the use of any solvent and additional chemicals during the polymerization process. Moreover, since synthesis can be performed directly on the surface of desired substrates, we can obtain uncontaminated polymer in various shapes. Taking those advantages into our consideration, we decided to employ the third CVD polymerization method in the preparation of PPV in various nano shapes including nanotubes, nanorods and nanofilms. Recently, Schafer et al.,(7l Staring and coworkers,... 

Plasma treatment and plasma deposition polymerization provides a unique and powerful method for the surface chemical modification of polymeric materials without altering their bulk properties. (7-5) These techniques offer the possibility to improve the performance of existing biomaterials and medical devices and for developing new biomaterials-(- -6)... 

Most PPX polymers are prepared by a unique chemical vapor deposition (CVD) polymerization method that was developed for coating components. In the CVD process the paracyclophane dimer is vaporized and the coating forms from a gaseous monomer without an intermediate liquid stage. As a result. 

Ring-opening anionic polymerization is used in the synthesis of polyferroce-nyldimethylsilane (PFS) (see section 9.6.3). This mechanism involves nucleophilic addition of a polymer anion to a cyclic monomer. The monomer then ring opens, leading to incorporation of the monomer into the growing chain and generation of a new anion. This method is not as common as those previously mentioned, but can result in well-defined polymers with unique chemical composition. 

Chapter 4 shows that the range of polymeric structures from enzymatic polymerization can be further increased by combination with chemical methods. The developments in chemoenzymatic strategies towards polymeric materials in the synthesis of polymer architectures such as block and graft copolymers and polymer networks are highlighted. Moreover, the combination of chemical and enzymatic catalysis for the synthesis of unique chiral polymers is discussed. 

In this article it has been shown, that the low temperature photopolymerization reaction of diacetylene crystals is a highly complex reaction with a manifold of different reaction intermediates. Moreover, the diacetylene crystals represent a class of material which play a unique role within the usual polymerization reactions conventionally performed in the fluid phase. The spectroscopic interest of this contribution has been focussed mainly on the electronic properties of the different intermediates, such as butatriene or acetylene chain structure, diradical or carbene electron spin distributions and spin multiplicities. The elementary chemical reactions within all the individual steps of the polymerization reaction have been successfully investigated by the methods of solid state spectroscopy. Moreover we have been able to analyze the physical and chemical primary and secondary processes of the photochemical and thermal polymerization reaction in diacetylene crystals. This success has been largely due to the stability of the intermediates at low temperatures and to the high informational yield of optical and ESR spectroscopy in crystalline systems. 

Nitroxide mediated SFRP, DPE mediated polymerization, ATRP, RAFT polymerization, etc. achieve polymerization control through the use of kinetic mediators or transfer agents, which protect a propagating free radical from imdesirable transfer and termination reactions. The emulsion block copolymer method is unique in that it does not require the use of any chemical mediators to achieve this control. Polymerization control is achieved by physically trapping radicals by... 

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