Polymers fluorenone

The principles needed to design a polymer of low flammability are reasonably well understood and have been systematized by Van Krevelen (5). A number of methods have been found for modifying the structure of an inherently flammable polymer to make it respond better to conventional flame retardant systems. For example, extensive work by Pearce et al. at Polytechnic (38, 39) has demonstrated that incorporation of certain ring systems such as phthalide or fluorenone structures into a polymer can greatly increase char and thus flame resistance. Pearce, et al. also showed that increased char formation from polystyrene could be achieved by the introduction of chloromethyl groups on the aromatic rings, along with the addition of antimony oxide or zinc oxide to provide a latent Friedel-Crafts catalyst. 

Although the exact mechanism of the fluorenone formation is not known, it is believed that the monoalkylated fluorene moieties, present as impurities in poly(dialkylfluorenes), are the sites most sensitive to oxidation. The deprotonation of rather acidic C(9)—H protons by residue on Ni(0) catalyst, routinely used in polymerization or by metal (e.g., calcium) cathode in LED devices form a very reactive anion, which can easily react with oxygen to form peroxides (Scheme 2.26) [293], The latter are unstable species and can decompose to give the fluorenone moiety. It should also be noted that the interaction of low work-function metals with films of conjugated polymers in PLED is a more complex phenomenon and the mechanisms of the quenching of PF luminescence by a calcium cathode was studied by Stoessel et al. [300],... 

Patents of Dow Chemicals first described 9,9-diaryl-substituted PF homopolymers 204 and 205 by Yamamoto polymerization of the corresponding 2,7-dibromo monomers [272], although the methods for monomer preparation were not described. For unsubstituted fluorenone, a convenient method for its conversion into 9,9-(4-hydroxyphenyl)-[307-309] and 9,9-(4-alkoxyphenyl)fluorenes [310] was reported previously, which included condensation of fluorenone with phenol or its ethers in acidic conditions (dry HC1 [308,309] or H2SO4 [307,311]) in the presence of (3-mcrcaptopropionic or mercaptoacetic acids. Both polymers 204 and 205 showed similar Mn 21,000 with PDI of 1.48 and 1.75, respectively, and spectral data typical for PF (205 Aabs = 389 (r 50,000 //(mol cm) APL = 417, 439, and 473 mn (THF)) (Chart 2.48). 

P. Scanducci de Freitas, U. Scherf, M. Collon, and E.J.W. List, (9,9-Dialkylfluorene- co-fluorenone) Copolymers containing low fluorenone fractions as model systems for degradation-induced changes in polyfluorene-type semiconducting materials, e-Polymers, Abstr. No. 009, 2002. 

Materials that exhibit photoconductivity and/or electrooptical response can be found in large numbers among molecular glasses (Fig. 3.40). Dihydropyridines with Tg 25 C and low tendency of crystallization have been used (e.g., 2BNCM, 73), adding only a small fraction of a binding polymer (<10%), and 2,4,7-trinitro-9-fluorenone (TNF) as a sensitizer [310]. A common strategy is... 

Figure 5.27 1-D polymer of (a) [Au3(MeN=COMe)3]-[2,4,5,7-tetranitro-9-fluorenone] (b) [Au3(MeN=COMe)3]-[2,4,7-trinitro-9-fluorenone] showing the Au- -C interactions.

In the first part of this chapter we review some basic concepts of photoconductivity which are followed by a renew of some experimental techniques and how these have been applied to characterize some of the well known polymeric systems such as poly(N-vinyl carbazole) (PVK) and the charge transfer complex of PVK and 2,4,7,trinitro-9-fluorenone (TNF). The second part of this chapter is a review of the extensive original and patent literature on a variety of photoconducting polymers. 

Recently, Tanikawa et all94) discussed the photoconductivity of poly[i-( i-N-carbazolyethyl)-L-glutamate] and its charge transfer complex with 2,4,7, -trinitro-9-fluorenone. The photocurrents in this polymer are about one order of magnitude smaller than those of PVK at all measured wavelengths. The complex with TNF has a peak photocurrent at 600 nm while the absorption spectrum of the polymer... 

Charge-transfer polymers were commercialized by IBM Corporation since about 1968 in xerographic copiers A drum covered by trinitro-fluorenone-polyvinyl carbazole polymer mixed with trinitrofluore-none replaced the expensive Se drum. 

Two families of transparent polycarbonate-silicone multiblock polymers based on the polycarbonates of bisphenol acetone (BPA) and bisphenol fluorenone (BPF) were synthesized. Incorporation of a 25% silicone block in BPA polycarbonate lowers by 100°C the ductile-brittle transition temperature of notched specimens at all strain rates silicone block incorporation also converts BPF polycarbonate into a ductile plastic. At the ductile-brittle transition two competing failure modes are balanced—shear yielding and craze fracture. The yield stress in each family decreases with silicone content. The ability of rubber to sustain hydrostatic stress appears responsible for the fact that craze resistance is not lowered in proportion to shear resistance. Thus, the shear biasing effects of rubber domains should be a general toughening mechanism applicable to many plastics. 

The first bipolar doped polymers described in the literature were mixtures of 2,4,7-trinitro-9-fluorenone (TNF) and poly(N-vinylcarbazole) (PVK) (Gill, 1972, 1974, 1976). Mixtures of TNF and PVK form a three-component system containing free TNF, TNF PVK charge-transfer units, and free PVK (Weiser, 1972). In TNF and the charge-transfer units, electron transport dominates, whereas in PVK only hole transport is observed. The variation of the room... 

Molecular donor-acceptor complexes, such as the complex formed between poly(N-vinylcarbazole) (PVK) and 2,4,7-trinitro-9-fluorenone (TNF), and dye-polymer aggregates were widely used as generation materials in early applications. Since these materials are not infrared sensitive, there has been increasing emphasis on pigments during the past two decades. Because of the long... 

Recent work focuses on non-classical mesogenes which are built up by self-assembly. One example is a family of polymers containing disk-like groups which form no liquid crystalline phase, but ean act as an electron acceptor or donor. Charge transfer complexation with a complementary low molecular mass compound induces nematic or columnar discotic liquid crystalline order [153,154]. Figure 13 demonstrates this with the example of a polyester, bearing electron-rich tetra(alkoxy)tri-phenylene-units in the main chain, mixed with the electron deficient aromatic 2,4,7-trinitro-9-fluorenone (TNF). While the pure polymer shows a non-ordered isotropic melt, a columnar phase appears on addition of TNF. 

The photoreduction of aromatic ketones by tertiary amines is reported [38] to proceed at rates which are substantially faster than those observed for the corresponding photoinduced hydrogen abstraction from, e.g. alcohols. A limit case is given by fluorenone, the photoreduction of which does not occur in alcohol, ether or alkane solution, but readily takes place in the presence of amines, tertiary amines being the most effective [39,40]. Xanthone has also been reported to be easily photoreduced by iV,A-dimethylaniline [41], but not by 2-propanol [42]. However, the oxidation of tertiary amines photosensitized by fluorenone and xanthone is much less efficient than when sensitized by benzophenone, apparently because of lower rates of hydrogen abstraction [43]. Fluorenone/tertiary amine systems have been used successfully to photoinitiate the polymerization of MMA, St, MA and AN [30,38,44] and rather similar results have been obtained in the photoinitiated polymerization of MA by the benzophenone/EtsN system [45]. Thus, the great variety of substrates participating in exciplex formation has been readily extended to polymer-based systems. 

On the basis of the above findings, it can be concluded that grafting efficiencies and curing rates for commercial systems may be improved more easily by employing polymers having pendant amino groups rather than fluorenone moieties. 

The resulting poly(styrene), which is expected to have tertiary amine groups attached at each end of the polymer chain, due to the well established termination mechanism by radical-radical combination, are used, under UV irradiation, in conjunction with 9-fluorenone as a photo-redox system for the free radical polymerization of MMA to yield MMA/St/MMA block copolymers (Scheme 37) ... 

Figure 10. Top liquid-phase absorbance spectrum of each component of a typical photorefractive polymer composite. Each component, A -vinylcarbazole (PVK), 2,4,7-trinitro-9-fluorenone (TNF), and typical chromophore (EHDNPB), is diluted in dichloromethane separately. (Absorption due to the solvent has been subtracted.) Bottom the absorbance of light in a solid sample due to the charge transfer complexation between PVK and TNF. The sample was prepared from a 9 1 ratio of PVK/ TNF. The extension of absorption to longer wavelengths is clear.

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