Electronic polymers mechanical

The initiating radicals are assumed to be SCN, ONO or N3 free radicals. Tris oxalate-ferrate-amine anion salt complexes have been studied as photoinitiators (A = 436 nm) of acrylamide polymer [48]. In this initiating system it is proposed that the CO2 radical anion found in the primary photolytic process reacts with iodonium salt (usually diphenyl iodonium chloride salt) by an electron transfer mechanism to give photoactive initiating phenyl radicals by the following reaction machanism ... 

Electron transfer mechanism Butler-Volmer kinetics and, 587 in electronically conducting polymers, 568... 

The affinity of Cgo towards carbon nucleophiles has been used to synthesize polymer-bound Cgo [120] as well as surface-bound Cjq [121]. Polymers involving G q [54, 68, 69] are of considerable interest as (1) the fullerene properties can be combined with those of specific polymers, (2) suitable fullerene polymers should be spin-coatable, solvent-castable or melt-extrudable and (3) fullerene-containing polymers as well as surface-bound Cgo layers are expected to have remarkable electronic, magnetic, mechanical, optical or catalytic properties [54]. Some prototypes of polymers or solids containing the covalently bound Cjq moiety are possible (Figure 3.11) [68,122] fullerene pendant systems la with Cjq on the side chain of a polymer (on-chain type or charm bracelet ) [123] or on the surface of a solid Ib [121], in-chain polymers II with the fullerene as a part of the main chain ( pearl necklace ) [123], dendritic systems III, starburst or cross-link type IV or end-chain type polymers V that are terminated by a fullerene unit For III and IV, one-, two-and three-dimensional variants can be considered. In addition, combinations of all of these types are possible. 

The same electron transfer was investigated in a polyethyleneoxide film known to be a polymer electrolyte capable of transporting ions. The electron transfer mechanism was analyzed to take place by both static and dynamic mechanisms,33) the electron transfer distance was estimated to be 1.7 nm, and the dynamic rate constant was 4.6 x 106 M 1s 1, which is two orders of magnitude lower than that in an aqueous solution. 

In this section, we describe the fabrication of metal complex oligomer and polymer wires composed of bis(terpyridine)metal complexes using the bottom-up method.11 13 This method has an advantage in fabricating organized structures of rigid redox polymer wires with the desired numbers of redox metal complexes. We also present a new electron-transport mechanism applicable to the organized redox polymer wires-coated electrode. 

Besides these monodentate ligands, many multidentate ones have been prepared and used in different fields of chemistry and only a few should be mentioned here. Rigid bidentate benzimidazole-based N-heterocyclic carbenes were successfully used to synthesize main-chain conjugated organometallic polymers 23, an interesting class of materials with desirable electronic and mechanical properties (Fig. 9) [110]. 

Hydroxytelechelic polymers can be synthesized via a photoinitiated radical process 49,50 76 77). This reaction resembles that of the redox system because an electron transfer mechanism is operative and the synthesis is carried out in aqueous solution. The reactive species is a complex ion such as Fe3+, X (OH-, Cl-, N". ..). The light absorption (hv) by the ionic species results in an electron transfer reducing the cation oxidation of the anion leads to a free radical X which initiates the polymerization. 

We have recently found that this free radical oxidation of the methyl groups is in fact not a major pathway in the photooxidation of poly(phenylene oxide). Instead, the oxidation apparently occurs through an electron-transfer mechanism on the backbone of the polymer not chemically involving the methyl groups at all. In this paper, we present evidence inconsistent with the free radical mechanism and supporting this novel pathway for polymer photooxidation. 

Electron-Transfer Mechanism. A mechanism consistent with our results is shown in Scheme III. In this mechanism an excited polymer repeating unit undergoes electron transfer with another unit to generate a radical cation and radical anion pair (7 and 8). 

Scheme III is not, however, the only possible electron-transfer mechanism. In the presence of oxygen, an electron may be transferred directly from the excited polymer repeating unit to oxygen, generating the radical cation and superoxide without the intermediate radical anion (Scheme VIII). Our flash photolysis experiments cannot rule out this possibility because the transients formed...

Bulk semiconductors and powders have been used as initiators for radical polymerization reactions [140-144], Recently the study has been extended to semiconductor nanoclusters [145-147]. It was found that polymerization of methyl methacrylate occurs readily using ZnO nanoclusters. Under the same experimental conditions, no polymerization occurred with bulk ZnO particles as photoinitiators [145], In a survey study, several semiconductor nanoclusters such as CdS and Ti02, in addition to ZnO, were found to be effective photoinitiators for a wide variety of polymers [146], In all cases nanoclusters are more effective than bulk semiconductor particles. A comparison of the quantum yields for polymerization of methyl methacrylate for different nanoclusters revealed that Ti02 < ZnO < CdS [146]. This trend is parallel with the reduction potential of the conduction band electron. The mechanism of polymerization is believed to be via anionic initiation, followed by a free-radical propagation step. 

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