Polymers with Electronic Functions

3 POLYMERS WITH ELECTRONIC FUNCTIONS 26.3.1 Conventional Approaches 

Two older ideas of how to make organic polymers conductive are obvious  

Providing an ion exchanger with a sufficient number of redox groups so that conduction can occur by a relay-type redox-change mechanism. Examples are hydroquinone-derived redox polymers and polyvinyl polymers with a tetrathia-fulvalene, ferrocene, or carbazole group, which have been found useful for research and analytical applications. 

Synthesis Basically, two methods are available, which both start (evidently) from suitable monomers (1) chemical synthesis, followed by doping, and (2) electrochemical synthesis directly in a doped state. 

Despite the name, the material is consistently represented as (CH) in most places, a formula that should definitely be replaced by (C2H2) not only to reflect correctly the name and genesis from acetylene monomer but also to facilitate comparison with 

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Yamamoto T Macromol Rapid Commun (2002) 23 583-606 n-Conjugated polymers with electronic and optical functionalities preparation by organometallic polycondensation, properties, and applications... 

Fig. 7.1 Examples of materials and applications as a function of ion and electron conductivity. The electrical insulators are bottom left, materials with high component permeability (a oc harmonic mean of (7eon and < ion) at the top right. Battery electrolytes are bottom right, while purely electronic conductors (electrical interconnects) are to be found at the top left. Between these four extremes there are materials for sensors, elec-trochromics, diodes, transistors and many other applications. The conductivity values only serve for a first orientation. In various cases, the windows can be substantially extended, e.g. heavy doping. The presentation is based on Refs. [535,536]. Polymers are not included in the figure because there are no reliable data on the relevant transference numbers. They are, however, impressive examples of how widely the conductivity properties can be varied. On the one hand there are (doped) polymers with electronic conductivities as high as Cu or Ru02 (cf. PA (I2) in Fig. 6.15). On the other hand there are (doped) polymers exhibiting appreciable ionic conductivities (cf. PEO (LiX) in Fig. 6.12) that typically range between 10 and 10 fi cm. ...

Polymers. The molecular weights of polymers used in high energy electron radiation-curable coating systems are ca 1,000—25,000 and the polymers usually contain acryUc, methacrylic, or fumaric vinyl unsaturation along or attached to the polymer backbone (4,48). Aromatic or aUphatic diisocyanates react with glycols or alcohol-terrninated polyether or polyester to form either isocyanate or hydroxyl functional polyurethane intermediates. The isocyanate functional polyurethane intermediates react with hydroxyl functional polyurethane and with acryUc or methacrylic acids to form reactive p olyurethanes. 

The latest review of the status and prospects of polymer electronics (Samuel 2000), by a young physicist working in Durham University, England, goes at length into the possibilities on the horizon, including the use of copolymer chains with a series of blocks with distinct functions, and the possible use of dendrimer molecules... 

Polymers have come a long way from parkesine, celluloid and bakelite they have become functional as well as structural materials. Indeed, they have become both at the same time one novel use for polymers depends upon precision micro-embossing of polymers, with precise pressure and temperature control, for replicating electronic chips containing microchannels for capillary electrophoresis and for microfluidics devices or micro-optical components. 

This review has shown that the analogy between P=C and C=C bonds can indeed be extended to polymer chemistry. Two of the most common uses for C=C bonds in polymer science have successfully been applied to P=C bonds. In particular, the addition polymerization of phosphaalkenes affords functional poly(methylenephosphine)s the first examples of macromolecules with alternating phosphorus and carbon atoms. The chemical functionality of the phosphine center may lead to applications in areas such as polymer-supported catalysis. In addition, the first n-conjugated phosphorus analogs of poly(p-phenylenevinylene) have been prepared. Comparison of the electronic properties of the polymers with molecular model compounds is consistent with some degree of n-conjugation in the polymer backbone. 

The polymers listed above, and all other linear polymers as well, are formed from monomers which enter into two, and only two, linkages with other structural units. This statement corresponds to the previous remark that the structural units of linear polymers necessarily are bivalent. The interlinking capacity of a monomer ordinarily is apparent from its structure it is clearly prescribed by the presence of two condensable functional groups in each monomer in the third and fourth examples above. The ability of the extra electron pair of the ethylenic linkage to enter into the formation of two bonds endows styrene with the same interlinking capacity. In accordance with the functionality concept introduced by Carothers, all monomers which when polymerized may join with two, and only two, other monomers are termed bifunctional. Similarly, a hifunctional unit is one which is attached to two other units. It follows that linear polymers are composed exclusively (aside from terminal units) of bifunctional units. ... 

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