Polymer synthesis photochemical polymerization

N-Benzyl and iV-alkoxy pyridinium salts are suitable thermal and photochemical initiators for cationic polymerization, respectively. Attractive features of these salts are the concept of latency, easy synthetic procedures, their chemical stability and ease of handling owing to their low hygroscopicity. Besides their use as initiators, the applications of these salts in polymer synthesis are of interest. As shown in this article, a wide range of block and graft copolymer built from monomers with different chemical natures are accessible through their latency. 

Neckers, D.C. (1988) Properties of Polymeric Rose Bengals - Polymers as Photochemical Reagents, in Synthesis and Separations Using Functional Polymers (eds D.C. Sherrington and P. Hodge), John Wiley Sons, Inc., New York, pp. 209-26. 

Jung, O.-S., and Pierpont, C. G., Photochemical polymers. Synthesis and characterization of a polymeric pyrazine-bridged cobalt semiquinonate-catecholate complex, J. Am. Chem. Soc., 116, 2229-2230 (1994). 

MOR 15] Morris J., Telitel S., Fairfull-Smith K.E. et al, Novel polymer synthesis methodologies using combinations of thermally- and photochemically-induced nitroxide mediated polymerization . Polymer Chemistry, 2015. 

YAG 97] Yagci Y., Endo T., N-benzyl and N-alkoxy pyridinium salts as thermal and photochemical initiators for cationic polymerization , Polymer Synthesis/Polymer Catalysis, Springer, Berhn Heidelberg, vol. 127, pp. 59-86, 1997. 

In addition to chemical and electrochemical synthesis, other polymerization methods such as photochemical synthesis, emulsion, and pyrolysis have been reported [58, 63]. In a recent study, a self-assembled monolayers (SAMs) method has been used to deposit thiolated poly(alkylthiophene)s and functionalized alka-nethiols [82]. The authors claimed that resulting polymers have low impedance at 1 kHz and are more robust and better controlled in their composition than existing electrodeposited conductive polymer coatings. 

There are additional factors that may reduce functionality which are specific to the various polymerization processes and the particular chemistries used for end group transformation. These are mentioned in the following sections. This section also details methods for removing dormant chain ends from polymers formed by NMP, ATRP and RAFT. This is sometimes necessary since the dormant chain-end often constitutes a weak link that can lead to impaired thermal or photochemical stability (Sections 8.2.1 and 8.2.2). Block copolymers, which may be considered as a form of end-functional polymer, and the use of end-functional polymers in the synthesis of block copolymers are considered in Section 9.8. The use of end functional polymers in forming star and graft polymers is dealt with in Sections 9.9.2 and 9.10.3 respectively. 

This article reports on the synthesis of photosensitive polymers with pendant cinnamic ester moieties and suitable photosensitizer groups by cationic copolymerizations of 2-(cinnamoyloxy)ethyl vinyl ether (CEVE) (12) with other vinyl ethers containing photosensitizer groups, and by cationic polymerization of 2-chloroethyl vinyl ether (CVE) followed by substitution reactions of the resulting poly (2-chloroethyl vinyl ether) (PCVE) with salts of photosensitizer compounds and potassium cinnamate using a phase transfer catalyst in an aprotic polar solvent. The photochemical reactivity of the obtained polymers was also investigated. 

The step-growth polymerization strategy used to incorporate metal-metal bonded units into polymers can also be used to incorporate metal clusters into polymers. One of only a few examples of this type of reactivity is shown by equation 11.35 It is noteworthy that metal clusters also undergo photochemical reactions.36,37 These reactions should also occur when the clusters are incorporated into polymer backbones. If polymers containing metal clusters can be shown to have unusual properties or applications (photochemical or otherwise), then the synthesis of these polymers will likely burgeon in coming years. 

In the section concerning the synthesis of hydroxytelechelic polymers initiated by thermally or photochemically decomposed hydrogen peroxide, the molecular weight distribution of polymers has been found to be dependent on solution homogeneity. A unimodal distribution of molecular weights is observed in vinyl acetate polymerization (true solutions), a bimodal one was found for polydienes, and sometimes a tri-modal one for poly(methyl methacrylate) (non-regular solutions). 

Polypyrroles (PPy s) are formed by the oxidation of pyrrole or substituted pyrrole monomers. In the vast majority of cases, these oxidations have been carried out by either (1) electropolymerization at a conductive substrate (electrode) through the application of an external potential or (2) chemical polymerization in solution by the use of a chemical oxidant. Photochemically initiated and enzyme-catalyzed polymerization routes have also been described but are less developed. These various approaches produce polypyrrole (PPy) materials with different forms—chemical oxidations generally produce powders, whereas electrochemical synthesis leads to films deposited on the working electrode, and enzymatic polymerization gives aqueous dispersions. The conducting polymer products also possess different chemical/electrical properties. These alternative routes to PPy s are therefore discussed separately in this chapter. 

By the photoreduction of H2PtCl6 in the presence of unsaturated surfactants (7 types), Pt clusters covered by polymeric micelles were obtained and further polymerized by UV radiation or by y-irradiation [290]. The formed clusters protected by polymerized micelles exhibited greater catalytic activity during the photochemical synthesis of H2 in the presence of EDTA/Ru(bpy)j /MV /Pt in aqueous solution than those clusters protected by linear polymers. The use of non-ionic surfactants resulted in the best catalytic activity. 

Polypyrrole and many of its derivatives can be synthesized via simple chemical or electrochemical methods [120]. Photochemically initiated and enzyme-catalyzed polymerization routes have also been described but less developed. Different synthesis routes produce polypyrrole with different forms chemical oxidations generally produce powders, while electrochemical synthesis leads to films deposited on the working electrode and enzymatic polymerization gives aqueous dispersions [Liu. Y. C, 2002, Tadros. T. H, 2005 and Wallace. G. G, 2003]. As mentioned above the electrochemical polymerization method is utilized extensively for production of electro active/conductive films. The film properties can be easily controlled by simply varying the electrolysis conditions such as electrode potential, current density, solvent, and electrolyte. It also enables control of thickness of the polymers. Electrochemical synthesis of polymers is a complex process and various factors such as the nature and concentration of monomer/electrolyte, cell conditions, the solvent, electrode, applied potential and temperature, pH affects the yield and the quality of the film... 

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