Polymerization electron donors

In another approach, the fact that crystalline monomeric charge transfer complexes exhibit electrical conductivity led to preparation of polymeric charge transfer complexes. These can be obtained from a polymeric electron donor and a monomeric election acceptor or from a polymeric acceptor and a monomeric donor, the former type being the more common, These polymers are not crosslinked and some are soluble, but their conductivities are generally low,... 

Alternating copolymer 20 derived from 2,7-dibenzosilole and 4,7-dithienyl-2,1,3-benzothiadiazole is an outstanding polymeric electron donor in photovoltaic cells.37 With an active layer made up of copolymer to PCBM in a 1 2 ratio, the solar cell displays a high short-circuit current of 9.5 mA/cm2, an open-circuit voltage of 0.9 V, and a fill factor of 50.7%, under illumination of an AM 1.5 solar simulator at 80 mW/cm2. The calculated energy conversion efficiency is 5.4%, which is one of the highest efficiencies so far reported for polymeric photovoltaic cells. 

Polymers containing benzoin terminal groups can act as photochemical macroinitiators and are effective in photogenerating polymeric electron donor radicals. The initiation of polymerization by means of azo-benzoin initiators yields polymers with one or two benzoin end-groups according to the termination mode of the particular monomer involved [72-74], The general synthetic procedure is depicted below as illustrated for the case styrene polymerization (Scheme 18). 

The most commonly used polymeric electron donors are PPV and poly(alkyl thiophene)s. Polymeric electron acceptors are cyano substituted PPV and poly(p-pyridyl vinylene). There are also low-molecular-weight electron acceptors, which include fiillerenes and perylene derivatives, such as tetrabenzyl perylene-3,4,9,10-tetracarboxylate. ... 

A substantial number of photo-induced charge transfer polymerizations have been known to proceed through N-vinylcarbazole (VCZ) as an electron-donor monomer, but much less attention was paid to the polymerization of acrylic monomer as an electron receptor in the presence of amine as donor. The photo-induced charge-transfer polymerization of electron-attracting monomers, such as methyl acrylate(MA) and acrylonitrile (AN), have been recently studied [4]. In this paper, some results of our research on the reaction mechanism of vinyl polymerization with amine in redox and photo-induced charge transfer initiation systems are reviewed. 

Alkali metals are obvious examples of electron donors, and indeed polymerization of butadiene or styrene initiated by metallic sodium results from an electron transfer initiation process. This reaction has been, and is still, being studied by many investigators, notably by Ziegler55 and by Russian workers.1 In Ziegler s notation the initiation is represented by the equation... 

Let us consider the conditions which favor the formation and survival of the dimeric and polymeric radical ions. This might be achieved by keeping the concentration of monomer high, the concentration of monomer" ions low and by removing the radical ions as rapidly as possible from the zone containing the primary electron donors. Moreover, since the radical ions dimerize, their average life time increases as their concentration decreases. The following experiment should probably produce the best results. 

This section describes polymerizations of monomer(s) where the initiating radicals are formed from the monomer(s) by a purely thermal reaction (/.e. no other reagents are involved). The adjectives, thermal, self-initialed and spontaneous, are used interchangeably to describe these polymerizations which have been reported for many monomers and monomer combinations. While homopolymerizations of this class typically require above ambient temperatures, copolymerizations involving certain electron-acceptor-electron-donor monomer pairs can occur at or below ambient temperature. 

On the basis of these studies we decided to carry out a series of AMI and IMA experiments (2) with the TMPCl/EtAlCl2/DtBP combination. Figures 1 and 2 show the results. The M versus Wp (g of poly(P-PIN) formed) plots and the N (number of moles of poly(P-PIN) formed) versus Wp plots (insets) indicate increasing deviation from the theoretical values (calculated for Ieff = 100%). According to these results chain transfer proceeds in these polymerizations, i.e., the systems are nonliving. Further experimentation would be necessary to develop satisfactory living conditions, in particular to investigate the effect of solvent polarity, temperature and electron donors on the mechanism. 

The ability to ionically polymerize apparently correlates in many cases with the capacity of the substituents to act as electron acceptors (anionic polymerizability) or as electron donors (cationic polymerizability) on the rt-bond of the vinyl group. These relationships should be visible in carefully chosen quantum chemical parameters. 

Further interesting redox modified polypyrrole films were prepared e.g. a polymeric copper phenanthroline complex that can be reversibly de- and re-metallated because it retains the pseudotetrahedral environment after decomple-xation, A very diversified electrochemistry is displayed by polypyrrole films containing electron donor as well as electron acceptor redox centers in the same film... 

Initial work was carried out with 3,9-bis(methylene-2,4,8,10-tetraoxaspiro[5,5] undecane) where R = H (11). However, this monomer contains two electron donor alkoxy groups on one double bond which is thus highly susceptible to a cationic polymerization. For this reason, the monomer is extremely difficult to handle and cannot be analyzed by gas chromatography since it does not survive passage through the column. It is prepared by the dehydrohalogen-ation reaction of the reaction product of pentaerythritol and chloro-acetaldehyde,... 

A corresponding anionic mechanism in the presence of a strong base (or electron donor) is plausible. Other cyclic compounds may be susceptible to polymerization by similar ionic mechanisms. Inasmuch as the growth step must be extremely rapid, a chain reaction is indicated and classification with vinyl-type addition polymerizations should be appropriate in such cases. 

Stannylenes are in the first place Lewis acids (electron acceptors) as can be easily derived from the structures of the solids (Chapter 3). When no Lewis bases (electron donors) are present, they may also act as Lewis bases via their non-bonding electron pair (see polymerization of organic stannylenes). 

In the polymerization of butadiene, Teyssie (52-54) has shown that certain electron donors, such as alcohols or phosphines, can convert tt-allylnickel chloride from a catalyst which forms c/j-polybutadiene to one which produces frans-polybutadiene. These ligands presumably block a site on the nickel atom, forcing the butadiene to coordinate by only one double bond. While alcohols cannot be added directly to the hexadiene catalyst (as they deactivate the alkylaluminum cocatalysts), incorporation of the oxygen atom on the cocatalyst places it in an ideal position to coordinate with the nickel. The observed rate reduction (52) when the cri-polybutadiene catalyst is converted into a fra/w-polybutadiene catalyst is also consistent with the observed results in the 1,4-hexadiene synthesis. 

Electron-donor end group, 20 504 Electron donors, in Ziegler-Natta polymerization, 26 518-521 Electron effective mass, in direct gap semiconductors, 22 143—144 Electronegativities, Pauling scale of,... 

Tertiary amines with an a-hydrogen are among the most effective electron donors other electron donors include alcohols, amides, amino acids, and ethers. A third process, direct hydrogen atom transfer from RH to the ketone, is not common hut does occur with some photoinitiators. The overall result is the same as the electron-transfer process. Although two radicals are produced by photolysis of the photoinitiator, only one of the radicals is typically active in initiation—the aroyl and amine radicals in Eqs. 3-48 and 3-49, respectively. The other radical may or may not initiate polymerization, hut is active in termination. The decrease in photoinitiator concentration during polymerization is referred to as photo-bleaching. 

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