Polymers with aromatic amine groups

Polymers with aromatic amine groups (and various substituents) comprise the most studied and best understood photoconductive and charge-transporting materials (Fig. 8.13). The arylamine transport-active groups are either part of the polymer structure or are mixed with the host polymer. One can easily recognize that PVK is a substituted aromatic amine. 

Other carbazole-containing polymers are also photoconductive [2]. Among the carbazole polymers studied in detail are poly(N-epoxy-propylcarbazole) [75], poly[y-08-N-carbazolylethyl)-L-glutamate] [76] and poly[ -(N-carbazolyl vinyl ether)] [77]. Charge mobilities in these polymers are comparable to those in PVK, but they form tougher, less brittle films. 

The photoresponse of arylamine-containing polymers can be extended to the visible range by copolymerizing the donor monomer with electron-accepting comonomers [78, 79]. For example, poly(N-methyl-3-hydroxy-methylcarbazoly acrylate-co-acryloyloxy-3 -hydroxypropyl 3,5-dinitro-benzoate) extends the photoresponse through the visible to the near infrared range [79]. 

The possible effect of spatial order on carbazole groups has been a subject of discussion. Isotactic poly[2-(N-carbazolyl)ethyl acrylate] exhibits a room-temperature hole mobility of 1.7 x 10 m V s at 2xlO Vm which is considerably higher than that of the atactic polymer or PVK [80]. On the other hand, these values are very close to those obtained for NIPC/polycarbonate at a comparable concentration of the transport-active molecule, i.e, a system with no order. Experiments with other carbazole polymers have shown that changing the backbone (e.g. carbon vinyl to siloxy) [45], or spacing of carbazole groups from the chain, has only a secondary effect. 

Among other recently obtained photoconductive polymers containing donor groups and an extended 7r-electron system is electrochemically polymerized poly(thionaphthene-indole) [81]. 

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Friedel-Crafts alkylation of various aromatic rings such as benzene, toluene or phenol lead to a variety of diaromatic products (equation 46). Nitration of this telechelic followed by reduction leads to a polymer with terminal amine groups. The phenol-terminated telechelics can be further derivatized as shown in Scheme 47. 57.458 Recently, tertiary esters and ethers were used in conjunction with BCI3 to provide the first example of a living carbocationic polymerization of isobutylene. Scheme 48 shows the polymerization mechanism suggested for initiation with tertiary esters. The resulting polymers are telechelics containing one or two tertiary chlorine chain ends. 

The end group of the polymers, photoinitiated with aromatic amine with or without the presence of carbonyl compound BP, has been detected with absorption spectrophotometry and fluororescence spectrophotometry [90]. The spectra showed the presence of tertiary amino end group in the polymers initiated with secondary amine such as NMA and the presence of secondary amino end group in the polymers initiated with primary amine such as aniline. These results show that the amino radicals, formed through the deprotonation of the aminium radical in the active state of the exciplex from the primary or secondary aromatic amine molecule, are responsible for the initiation of the polymerization. 

The susceptibility of cyclodisilazanes to nucleophilic attack by aromatic amines has also been used to prepare silazane containing polymers. Polysilazane cyclo-linear chains with aromatic spacing groups, synthesized by polycondensations of difunctional cyclodisilazanes with bis-phenols and N.N -diorganosilane diamines, have been reported (13). 

The following photoconductive polymers can also be clarified as polymers of aromatic amines poly(N-vinylphenothiazine) and poly(N-vinylphenoxazine ° and poly(N-acrylodibenzazepine) ° Poly(N-vinylcarbazole) is basically a modified vinyldiphenylamine polymer . It has yet to be detemined if the transport characteristics of PVK with the diphenyl amino group forced into planarity are different from those of poly(N-vinyldiphenylamine) which would possess a greater freedom of rotation. The properties of PVK have been discussed in many articles and reviews [for example see Ref. ]. Several articles and patents have been published recently which deal with carbazole containing polymers other than PVK, and copolymers of N-vinylcarbazole with some other monomers. 

Of special practical interest in spinning from solution of some polymers may become the macroradicals reactions with aromatic diamines. In this way, chemically modified polymers -containing free aromatic aminic-groups may be obtained. In their turn, they may be either diazotized or coupled with phenols or tertiary mixtures of amines, azoic structures being thus formed at the ends of the macromolecular chains. Depending on the chemical nature of the coupling agent employed, different colorations may results ... 

Solvent for Displacement Reactions. As the most polar of the common aprotic solvents, DMSO is a favored solvent for displacement reactions because of its high dielectric constant and because anions are less solvated in it (87). Rates for these reactions are sometimes a thousand times faster in DMSO than in alcohols. Suitable nucleophiles include acetyUde ion, alkoxide ion, hydroxide ion, azide ion, carbanions, carboxylate ions, cyanide ion, hahde ions, mercaptide ions, phenoxide ions, nitrite ions, and thiocyanate ions (31). Rates of displacement by amides or amines are also greater in DMSO than in alcohol or aqueous solutions. Dimethyl sulfoxide is used as the reaction solvent in the manufacture of high performance, polyaryl ether polymers by reaction of bis(4,4 -chlorophenyl) sulfone with the disodium salts of dihydroxyphenols, eg, bisphenol A or 4,4 -sulfonylbisphenol (88). These and related reactions are made more economical by efficient recycling of DMSO (89). Nucleophilic displacement of activated aromatic nitro groups with aryloxy anion in DMSO is a versatile and useful reaction for the synthesis of aromatic ethers and polyethers (90). 

Aromatic electrophilic substitution is used commercially to produce styrene polymers with ion-exchange properties by the incorporation of sulfonic acid or quaternary ammonium groups [Brydson, 1999 Lucas et al., 1980 Miller et al., 1963]. Crosslinked styrene-divinyl-benzene copolymers are used as the starting polymer to obtain insoluble final products, usually in the form of beads and also membranes. The use of polystyrene itself would yield soluble ion-exchange products. An anion-exchange product is obtained by chloromethylation followed by reaction with a tertiary amine (Eq. 9-38) while sulfonation yields a cation-exchange product (Eq. 9-39) ... 

The modification of lignins with chlorophosphazenes allows the manufacture of products characterized by flame resistance and thermal stability. This can be attributed to the aromatic structure of the lignin-phosphazene polymer as well as to the presence of such flame inhibiting elements as phosphorous, nitrogen and sulfur. Other useful properties may also result from this combination. It has previously been reported (8-13) that the modification provides crosslinked products with suitably low chlorine content. This is a consequence of incomplete substitution of the phosphazenes cycles. Additional modification of the reaction products by chemical compounds with reactive hydroxyl or amine groups reduces the unreacted chlorine content and improves product properties (8-13). Some properties of the derivatives obtained are presented in Table I. 

The liquid polymer is converted to the rubbery state by reagents that react with mercaptan (-SH) and side groups of the polymer segments by oxidation, addition or condensation to effect sulfide (-S-S-) bond formation. The oxidation reactions are exothermic and accelerated by an alkaline environment. The most commonly employed oxidizing agents which are suitable for curing liquid polymers are cobalt or manganese or lead octoate, p-quinonedioxime and di- or tri-nitrobenzene. Epoxy resin also reacts with liquid polysulfide polymers by addition in the presence of an aliphatic or aromatic amine and polyamide activator as shown in Equation 5.8 ... 

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