Polymer ion radicals

In order to understand the nature of electron transfer dynamics in polymers, it is necessary to understand the electronic structure of polymer ion radicals and their interaction with the counter ion. These are closely related to configurational and conformational structures of polymers. Similar concerns occur in fluorescence studies of polymers where one finds that the electronic properties of the excited singlet state are sensitive to the structure of the main chain, the molecular weight of the polymer, and the position of the chromophore in the polymer structure. These factors determine the statistical distributions of inter-chromophoric distance and relative orientation resulting in characteristic fluorescence behavior. A similar relationship... 

The most interesting aspect of decay dynamics of polymer ion radicals is that slow geminate recombination is observed even in polar solvents. During our systematic studies of carbazole polymers quenched by DMTP in N,N-dimethylformamide, we found that the decay of the ion radicals produced had both of the fast and slow components. Although only normal second-order decay kinetics could be observed in the cases of small molecule donor-acceptor systems and of polymers with low degree of polymerization, an additional first-order decay was detected for PVCz with n-values of 400 and... 

The method of preparation of radical ions used in this work is widely known in the field of radiation chemistry (3, 11,12). The radical ions of the solute are produced by a charge- (hole- or electron-) transfer process from y-irradiated low temperature matrices. This method is applicable for the formation of radical ions of polymers including polysilanes (7, 3), and a number of reports about polymer ion radicals have been published so far (72). However, some problems exist in formation of polymer radical ions because of their low solubility and the tendency to be aggregated in low-temperature matrices. Under such conditions. 

A number of methods such as ultrasonics (137), radiation (138), and chemical techniques (139—141), including the use of polymer radicals, polymer ions, and organometaUic initiators, have been used to prepare acrylonitrile block copolymers (142). Block comonomers include styrene, methyl acrylate, methyl methacrylate, vinyl chloride, vinyl acetate, 4-vinylpyridine, acryUc acid, and -butyl isocyanate. 

Microwave or radio frequencies above 1 MHz that are appHed to a gas under low pressure produce high energy electrons, which can interact with organic substrates in the vapor and soHd state to produce a wide variety of reactive intermediate species cations, anions, excited states, radicals, and ion radicals. These intermediates can combine or react with other substrates to form cross-linked polymer surfaces and cross-linked coatings or films (22,23,29). 

The progression of an ideal emulsion polymerization is considered in three different intervals after forming primary radicals and low-molecular weight oligomers within the water phase. In the first stage (Interval I), the polymerization progresses within the micelle structure. The oligomeric radicals react with the individual monomer molecules within the micelles to form short polymer chains with an ion radical on one end. This leads to the formation of a new phase (i.e., polymer latex particles swollen with the monomer) in the polymerization medium. 

Water is extensively used to produce emulsion polymers with a sodium stearate emulsifrer. The emulsion concentration should allow micelles of large surface areas to form. The micelles absorb the monomer molecules activated by an initiator (such as a sulfate ion radical 80 4 ). X-ray and light scattering techniques show that the micelles start to increase in size by absorbing the macromolecules. For example, in the free radical polymerization of styrene, the micelles increased to 250 times their original size. 

Electroactive donors, such as TTF or triarylpyrazoline, can be bound in high yield to polymeric matrices. The TTF linear polymers show interesting cooperative properties (i.e., ion-radical cluster formation) that is not observed for the isolated monomers in solution or the low coverage polymers. Furthermore, thin solid films of these donors bound to cross-linked polymer backbones display remarkably facile charge transport through the film bulk which is accompanied by dramatic and reversible optical changes. 

Polymeric ion-radicals are usually formed as a result of one-electron redox modifications of uncharged polymers containing electrochemically active groups. They attract an enhanced attention in the sense of possible practical applications. Because polymeric ion-radicals contain many spin-bearing groups, a similarity emerges between polymeric ion-radicals and poly(ion-radicals). 

This kind of polymerization is used for preparation of polymers for special applications. In the preparative scale, ion-radical mechanopolymerization is accompanied with mechanodepolymeriza-tion. Although the latter process does not always include the ion-radical stage, mechanopolymerization and mechanodepolymerization should be discussed cojointly. 

In the H-shaped tube, all processes take place in a slow, controlled way. One simple modification consists of separating the two halves of the H-shaped tnbe with a fitted glass disk (medium, fine, or ultra-fine porous) to slowdown the diffusion. Another modification involves diffusion inside the reaction solvent containing a polymer. In this case, diffusion is retarded due to an increase of the solution viscosity (Scott et al. 1974, Berg et al. 1976). Sometimes, the synthesis of ion-radical salts is conducted ultrasoni-cally if the starting materials are insoluble in the desired solvents (see, e.g., Neilands et al. 1997). 

Absorption due to main intermediates such as polymer cation radicals and excited states, electrons, and alkyl radicals of saturated hydrocarbon polymers had not been observed for a long time by pulse radiolysis [39]. In 1989, absorption due to the main intermediates was observed clearly in pulse radiolysis of saturated hydrocarbon polymer model compounds except for electrons [39,48]. In 1989, the broad absorption bands due to polymer excited states in the visible region and the tail parts of radical cation and electrons were observed in pulse radiolysis of ethylene-propylene copolymers and the decay of the polymer radical cations were clearly observed [49]. Recently, absorption band due to electrons in saturated hydrocarbon polymer model compounds was observed clearly by pulse radiolysis [49] as shown in Fig. 2. In addition, very broad absorption bands in the infrared region were observed clearly in the pulse radiolysis of ethylene-propylene copolymers [50] as shown in Fig. 3. Radiation protection effects [51] and detailed geminate ion recombination processes [52] of model compounds were studied by nano-, pico-, and subpicosecond pulse radiolyses. 

Since sulfur from the persulfate does not appear in the polymer, two possible reactions were suggested. The sulfate ion-radicals may initiate the polymerization to produce fluoroalkyl sulfuric acid esters which would be very rapidly hydrolyzed. 

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