High conjugated polymers

An exciting development in polymer chemistry has been the synthesis of highly conjugated polymers, including polyacetylene. This is due to their... 

Abstract In situ spectroscopy is an important tool to characterize polymers synthesized via a precursor route. Highly conjugated polymers such as po y(p-phenylene vinylene) (PPV) and PPV derivatives are commonly prepared from a precursor polymer because the final polymers are very insoluble and intractable. Preparation in the precursor form enables the polymer materials to be cast as films. The PPV polymers are obtained from the precursor forms using a thermal elimination reaction. The exact conditions of the reaction are important as they influence the properties of the resultant polymer. The details of this thermal elimination reaction have been analyzed using thermal gravimetric analysis (TGA) coupled with infrared analysis of the evolved gas products. In situ infrared spectroscopy of the precursor films during thermal conversion to the polymers has provided further details about the elimination reaction. We have characterized PPV synthesized from a tetrahydrothiophenium monomer (sulfonium precursor route) and via the xanthate precursor route. PPV derivatives under study include poly(2,5-dimethoxy-p-phenylene vinylene) and poly(phenoxy phenylene vinylene). 

In the second type of infrared analysis, the spectral changes that occur in the polymer film are monitored during the reaction by the use of a heated infrared cell. Spectra are continuously taken of the polymer film as it is heated and converted from the precursor form to the final PPV product. These two methods of analysis are complementary and lead to a full characterization of the thermal elimination reaction in the formation of these highly conjugated polymers. The details of the thermal elimination are important because the conditions during the thermal elimination are known to influence the properties of the resultant polymer. 

Electrically conducting, highly conjugated polymers continue to fascinate scientists and to be the subject of many publications. This chapter addresses the recent research activity in this field and will thus concentrate on publications since the second edition of this handbook was published in 1998. For the most part. Chapter 11 [1] covered the literature through 1995 and so we wiU, in this updated chapter, cover the literature from 1995 to 2005. 

Synthesis of poly (2,5 bis(2-thienyl) 3-alkylthiophene) and poly (1-4 bis(2 thienyl) 2,5-dialkoxy phenylene) Several authors [132-6] reported that highly conjugated polymers can be prepared by the oxidative polymeriza-... 

The high sensitivity of the silicon atom offers new synthetic routes to polythiophene. As shown by infiared, Raman and photoluminescence criteria, silicon activates the selective coupling of thiophene units, leading to highly conjugated polymers with improved physical properties. 

Living polymerization using titanacyclobutane initiators enabled also the preparation of block copolmers by sequential addition of different monomers [114-116] and synthesis of highly conjugated polymers and block copolymers of 3,4-diisopropylidene-cyclobutene [116]. 

ROMP of cyclooctatetraene yields polyacetylene. This was reported by Korshak et al. for the first time [399]. Highly conjugated polymers are available via ROMP of cyclooctatetraene derivatives using a W- or Mo-based Schrock catalyst, too [20]. The physical properties of the polymers e.g., the conductivity after a doping process, may enable interesting applications of these materials [1,348]. 

Diacetylenes in phospholipid bilayers have been the subject of extensive studies in our laboratory, not only because of the highly conjugated polymers they form, but also because of their ability to transform bilayers into interesting microstructures. Consequent to our synthesis and characterization of several isomeric diacetylenic phospholipids, we have found that the polymerization in diacetylenic bilayers is not complete. In order to achieve participation of all diacetylenic lipid monomer in the polymerization process, diacetylenic phospholipid was mixed with a spacer lipid, which contained similar number of methylenes as were between the ester linkage and the diacetylene of the polymerizable lipid. Depending upon the composition of the mixtures different morphologies, ranging from tubules to liposomes, have been observed. Polymerization efficiency has been found to be dependent on the composition of the two lipids and in all cases the polymerization was more rapid and efficient than the pure diacetylenic system. We present the results on the polymerization properties of the diacetylenic phosphatidylcholines in the presence of a spacer lipid which is an acetylene-terminated phosphatidylcholine. 

In a 2012 EC-STM investigation, Tanoue et al. prepared highly conjugated polymer adlayers in situ by polycondensation of combinations of aromatic diamines and dialdehydes on Au(lll), some of which polymerized only on the surface but not in solution (see Figure 20.30). Highly ordered arrays were only observed in a relatively narrow range between +0.70 and +0.90 V versus RHE,... 

The most stable (and therefore the most intensely studied) EAPs are the oxidized, cationic salts of highly conjugated polymers, although stability varies widely with chemical composition. Some cationic salts are quite stable in air (40), while others are highly reactive. The cationic salts (or p-doped polymers) are obtained by oxidation (chemical or electrochemical) of neutral polymers or of monomers. Chemical oxidation in this context refers to the removal of electrons using a chemical oxidant such as ferric chloride (43), whereas... 

There are two main classes of materials from which OLED devices can be made, low-molar-mass compounds, often referred to as small molecules, which are deposited by vacuum evaporation [1] and mainchain, highly conjugated polymers, which are processed from solution by ink-jet printing, for example [10]. A hole injection layer is often used as the first layer on top of the conductive indium tin oxide (ITO) coated substrate. This layer can be either an evaporated small molecule, such as copper phthalocyanine, or a conductive polymer like poly(3,4-ethylenedioxythiophene) (PEDT) shown in Fig. 7.3 [11]. The role of the hole injection layer is to match the HOMO levels of the ITO and the hole transport materials, such as aromatic amines, and, especially in the case of PEDT, to planarise the rough ITO surface. 

The chemical structures of a number of mainchain, highly conjugated polymers used in OLEDs are shown in Fig. 7.6. The electroluminescence of the polymer poly(l,4-phenylenevinylene) (PPV) was reported in 1990 [10], Since PPV itself is completely insoluble and thin films are only accessible by thermal conversion of a soluble polyelectrolyte precursor, a number of soluble PPV-derivatives have been developed. Among these are MeH-PPV [20] and a number of soluble PPVs... 

---