Polymerization Yamamoto method

Yamamoto Method. Yamamoto et al. [423] prepared polythiophene by treating 2,5-dibromothiophene with Mg and catalyzing the polymerization by Ni(bipyridine)2Cl2 (Fig. 15). A similar... 

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). 

Actually, f(e) of a polymerizing plasma is expected to be non-Maxwelllans, and it is thus necessary to measure the exact form f(e) in order to estimate the true values of Tg and ng. Determinations of f(e) were carried out through the floating asymmetrical triple probe method (ATPM) developed by Okuda and Yamamoto ( ). 

Several electron diffraction studies have also been published by Pradere and Boudet [176,177,178]. The decision between a monoclinic or an orthorhombic cell cannot be made in their work, but an indexing based on a monoclinic cell is presented [178] a = 8.06 0.10 A, 6 = 5.55 0.04 A, c = 4.30 0.04A and j8=l00°. PPPs prepared by chemical and electrochemical methods are compared. The presence of lamellar crystals in Yamamoto and Fauvarque (electiochemical) PPP is attributed to the low degrees of polymerization (DP) of about 20. Kovacic PPP is the least crystalline of the PPPs investigated. Still, it is the best conductor, probably owing to its fibrillar nature. 

Polymerization of thiophenes can be carried out in many different ways and the most commonly used methods can be generalized into three categories (i) electropolymerization, (ii) metal-catalyzed coupling reactions and (iii) chemical oxidative polymerization. Electropolymerization is a widely used method to prepare insoluble films of PTs and represents a simple and efficient way to study the optical and electronic properties of PTs [4], although it is rarely used in the preparation of electroluminescent materials. In 1980, Yamamoto et al. reported the Ni-catalyzed polycondensation of 2,5-dibromothiophene 1. The latter was allowed to react with Mg in THF, affording 2-magnesiobromo-5-bromothiophene 2, which in the presence of Ni(bipy)Cl2 (bipy = 2,2 -bipyridyl) produced PT 3 (Scheme 19.2) [15], In the same year, Lin and Dudek described another example of a metal-catalyzed route to unsubstituted PT 3, exploiting acetylacetonates of Ni, Pd, Co and Fe as catalysts [16]. 

Pomerantz et al. were the first to study the effect of carboxylic groups on the PL properties of photoluminescence. Interestingly, the synthetic method [Ullmann polymerization on Cu powder or Yamamoto polymerization with Ni(0) catalyst] affects the fluorescence properties of the resulting polymer (lla,b) [38]. Both polymers revealed close molecular weights (Afn 3000), although the Cu-prepared polymers showed less defects and lower polydispersity. Consequently, PL emission maxima for the Cu-prepared polymers lla,b were red shifted compared with the Ni-prepared polymers [by 13-15 nm ( 0.05-0.06 eV) in solution and 25-30 nm ( 0.08-0.10 eV) in films. Table 19.1]. This emphasizes that the properties of the polymer depend on the preparation method and, consequently, conclusions drawn from small shifts of 0.05-0.1 eV in PL/EL energies of the materials prepared by different methods may not always be valid. 

The Yamamoto polymerization is an A A type, which uses dibromide compounds as monomers. Therefore, a bromination step is required during monomer synthesis, as shown in Scheme 5.2. Initially, researchers extended the first method from the already known synthesis of 9,9-dialkylfluorenes. Lately, scientists have preferred the second route, which can be scaled more easily. When polymer chemists design new polymer structures, they often consider scalable synthetic... 

The Yamamoto polymerization using Ni(COD)2 requires a nearly stoichiometric amount of the reagents. Therefore, the use of catalytic amounts of a Ni complex is of interest. Carter s group developed an organolithium-activated nickel-catalyzed polymerization using a Ni(II) complex, Ni(dppp)Cl2. Under the optimum conditions, the obtained PDHF showed M = 33 400 and PDI = 2.07. The above-mentioned methods are shown in Scheme 5.6. 

Mentioned below are broadly eleven ways of synthesizing these polymers Method A Electrochemical Polymerization Method B Solution Polymerization Method C In situ Chemical Oxidative Polymerization Method D Dispersion Polymerization Method E Vapor-Phase Polymerization Method F SoUd-State Polymerization Method G Solvent-Free Chemical Polymerization Method H Grignard Metathesis (GRIM) Polymerization Method I Direct C-H Arylation Polymerization Method J Stille Polymerization Method K Yamamoto Polymerization... 

When R = H or CH3 the polymer precipitated from the reaction mixture. PPP prepared by this method shows the same IR features as that reported by Yamamoto. However, the average DP of these materials was not estimated. Poor agreement between calculated and analytical data was interpreted as indicating low degrees of polymerization. 

Ueda et al. polymerized 3-phenyl-2,5-dichlorothio-phene by zerovalent nickel which was generated in situ by the reduction of nickel chloride with zinc powder in the presence of triphenylphosphine in DMF [98]. This is called Collon s method and is applicable to condensation of substrates bearing other fimctional groups such as the carbonyl group. Yamamoto et al. polymerized 3-formyl-, 3-hydroxyiminomethyl- and 3-cyano-2,5-dibromo1hiophenes [99]. The yields were 81%, 18% and 24%, respectively. was in the range of 520-630. 

The synthetic methods used to polymerize the 3-alkyl thiophene do not differ substantially from these employed for thiophene. The good choice of the solvent is important to ensure a complete dissolution of the monomer and the electrolyte in the electrosynthesis case. Chemically polymerization is based on the Grignard coupling method used by Yamamoto et al. [71] and later revised by Kobayashi et al. [72]. Some polymerizations carried out with chemical oxidants are also known with poly(3-alkyl-thiophene) [73]. 

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