Soluble precursor routes

Poly(arylene vinylenes). The use of the soluble precursor route has been successful in the case of poly(arylene vinylenes), both those containing ben2enoid and heteroaromatic species as the aryl groups. The simplest member of this family is poly(p-phenylene vinylene) [26009-24-5] (PPV). High molecular weight PPV is prepared via a soluble precursor route (99—105). The method involves the synthesis of the bis-sulfonium salt from /)-dichloromethylbenzene, followed by a sodium hydroxide elimination polymerization reaction at 0°C to produce an aqueous solution of a polyelectrolyte precursor polymer (11). This polyelectrolyte is then processed into films, foams, and fibers, and converted to PPV thermally (eq. 8). 

The scope of Wessling route has been extended by Mullen and co-workers to develop a soluble precursor route to poly(anthrylene vinyiene)s (PAVs) [51]. It was anticipated that the energy differences between the quinoid and aromatic resonance structures would be diminished in PAV relative to PPV itself. An optical band gap of 2.12 eV was determined for 1,4-PAV 29, some 0.3 eV lower than the value observed in PPV. Interestingly, the 9, lO-b/.v-sulfonium salt does not polymerize, possibly due to stcric effects (Scheme 1-9). 

Thus, N-pyrimidine phthalimide reacted with hexylamine at room temperature to form an amide-amide. The initial amide-amide formation proceeded more rapidly in chloroform as compared to dimethylsulfoxide (DM SO). However, the ring closure reaction to the imide was favored by the more polar, aprotic DMSO solvent, yielding the imide in nearly quantitative yield after 3 hours at 75 °C. The authors were able to utilize this synthetic approach to prepare well-defined segmented poly(imide-siloxane) block copolymers. It appears that transimidi-zation reactions are a viable approach to preparing polyimides, given that the final polyimide has a Tg sufficiently low to allow extended excursions above the Tg to facilitate reaction without thermal decomposition. Additionally, soluble polyimides can be readily prepared by this approach. Ultimately, high Tg, insoluble polyimides are still only accessable via traditional soluble precursor routes. 

As utilized in the synthesis of PPV-based polymers, soluble precursor routes have been developed for the synthesis of various heterocyclic Jt-conjugated polymers. The two most widely employed of these methods for heterocycle formation, shown in Scheme 66, center around ring closure of pre-polymers containing diacetylene 65 or 1,4-diketone units 66 [335-339]. The synthesis of heterocyclic structures from 1,4-diketones has been a known transformation in organic chemistry for decades. While once mainly used for monomer preparation through various cyclizations, it is now being employed to make heterocycle-containing polymers and copolymers [340-342]. 

Synthetic chemists can play a vital role by designing chemical approaches for processing of important nonlinear materials. Two specific examples presented here are (a) Soluble precursor route and (b) Chemical derivatization for improving solubility. 

In the soluble precursor route, a suitable precursor is synthesized which can be cast into a device structure (i.e., film) by using solution processing. Then it can be converted into the final nonlinear structure upon subsequent treatment (such as heat treatment). This approach has been used for poly-p-phenylenevinylene (PPV) as shown below (32) ... 

PPV derivatives can be prepared by water-soluble precursor route [14-16] involving sulfonium polyelectrolyte or organic-soluble precursor route [3,17,18] involving alkoxy substituted non-ionic form, respectively. The representative synthetic pathways for PPV derivatives are shown in Scheme 1. 

Son, S., Lovinger, A.J., Galvin, M.E., 1995. A simple organic-soluble precursor route to PPVfor highly efficient and pin-hole free LED devices. Polym. Mater. Sci. Eng. 72, 567-568. 

Soluble main chain oxadiazole polymers can be realised using solubilizing side groups such as tert-bu y and long flexible alkoxy or alkyl groups. Alternatively, flexible spacers can be incorporated between aromatic oxadiazole units, and finally a soluble precursor route may be employed. 

An important soluble precursor route for PPV and related polymers involves the polymerization of 1,4-bis(chloro-methyl or bromomethyl) arenes by treatment with potassium-f-butoxide in nonhydroxylic solvents like tetrahydrofuran. This methodology was first used by Gilch and Wheelright [111] as one of the most successful early PPV synthesis. 

Murase et al. prepared poly(2,5-thienylene vinylene) via a soluble precursor route, which had been successfully applied to the synthesis of poly(l,4-phenylene vinylene) [130]. This procedure is called the sulfonium salt process or soluble precursor route. The precursor polymer was obtained by dialysis of an alkaline solution of (74). It was insoluble in water, which was different from the precursor polymer of poly(/>-phenylene vinylene). However, the present precursor was soluble in polar solvents such as DMF and tetrahydrofuran and did not show IR bands due to the sulfonium salt but strong bands at 1664 and... 

As stated in Section 9.2, PTV prepared by a soluble precursor route yields bipolaronic charge carriers upon either photochemical or chemical oxidation. We have previously reported both the syntheses and doping studies of a series of PTV oligomers [37]. Oxidative doping of these oligomers up to the pentamer level can... 

The significant solubility improvement achieved by replacing phenyl rings with thiophene units led us to attempt the same with fused three-ring anthracene equivalents. Pomerantz et al. [46] have recently described the synthesis of such equivalents in their preparation of dithiophene fused PPV via a soluble precursor route. 

Soluble polythiophenes, 317 Soluble precursor route, 295 Solvatochromism, 329, 593 Solvent and solution pH, 431 Spectroelectrochemistry, 834 Spectroscopic methods, 535 Spin density, 837 Spiro oligothiophenes, 635 Structural analysis, 3 Structural nature, 2 Structure of polytoluidines, 575 Substituted polyanilines, 532, 619 Substituted pyrroles, 442 Sulfonates, 833... 

The soluble precursor routes are the most widely used methods to obtain processible, high-quality films of high-molecular-weight (up to over 1,000,000) PPVs and analogous polymers and copolymers. 

Although the soluble precursor route to conducting PA has offered a number of advantages in terms of processability and stability, the fact remains that the doped polymer is still difficult to process and is unstable in air. 

Arylene vinylene polymers, such as poIy(p-phenylene-vinylene) (PPV) and poly(2,5-thienyleneviryIene) (PTV) have been studied extensively over the past 10 years due to the relative ease of producing high quality thin films via the soluble precursor route [48-52]. PPVs in particular have been shown to be true multifunctional materials, displaying enhanced third-order NLO properties as well as applications as light-emitting diodes [53,54]. PPV pre-... 

K.-Y. Jen, M. Maxfield, L. W. Schacklette, and R. L. Eisenbaumer, Highly conducting poly(2,5-thienylene vinylene) prepared via a soluble precursor route, J. Chem. Soc., Chem. Commun. 309 (1987). 

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