Oxidative Coupling Polymerizations

Oxidative coupling polymerizations represent a general reaction for the preparation of high molecular weight linear polymers from many 2,6-di- and... 

The halogen displacement polymerization proceeds by a combination of the redistribution steps described for oxidative coupling polymerization and a sequence in which a phenoxide ion couples with a phenoxy radical (eq. 11) and then expels a bromide ion. The resultant phenoxy radical can couple with another phenoxide in a manner that is analogous to equation 11 or it can redistribute with other aryloxy radicals in a process analogous to equations 7 and 8. 

S. Amou, O. Haba, K. Shirato, T. Hayakawa, M. Ueda, K. Takeuchi, and M. Asai, Head-to-tail regioregularity of poly(3-hexylthiophene) in oxidative coupling polymerization with FeCl3, J. Polym. Sci., Part A Polym. Chem., 37 1943-1948, 1999. 

Oxidative coupling polymerization provides great utility for the synthesis of high-performance polymers. Oxidative polymerization is also observed in vivo as important biosynthetic processes that, when catalyzed by metalloenzymes, proceed smoothly under an air atmosphere at room temperature. For example, lignin, which composes 30% of wood tissue, is produced by the oxidative polymerization of coniferyl alcohol catalyzed by laccase, an enzyme containing a copper complex as a reactive center. Tyrosine is an a-amino acid and is oxidatively polymerized by tyrosinase (Cu enzyme) to melanin, the black pigment in animals. These reactions proceed efficiently at room temperature in the presence of 02 by means of catalysis by metalloenzymes. Oxidative polymerization is observed in vivo as an important biosynthetic process that proceeds efficiently by oxidases. 

Catechol melanin, a black pigment of plants, is a polymeric product formed by the oxidative polymerization of catechol. The formation route of catechol melanin (Eq. 5) is described as follows [33-37] At first, 3-(3, 4 -dihydroxyphe-nyl)-L-alanine (DOPA) is derived from tyrosine. It is oxidized to dopaquinone and forms dopachrome. 5,6-Dihydroxyindole is formed, accompanied by the elimination of C02. The oxidative coupling polymerization produces a melanin polymer whose primary structure contains 4,7-conjugated indole units, which exist as a three-dimensional irregular polymer similar to lignin. Multistep oxidation reactions and coupling reactions in the formation of catechol melanin are catalyzed by a copper enzyme such as tyrosinase. Tyrosinase is an oxidase con-... 

Kinetically slow steps in the formation of melanin from DOPA are the formation of dopaquinone from DOPA (step 1, kD), the reaction of dopachrome to dihydroxyindole (step 2), and the polymerization to form melanin (step 3, kM). Step 1 and step 2 proceed with about the same rate in the oxidative coupling polymerization catalyzed by tyrosinase. However, step 1 becomes remarkably slow when a macromolecule-metal complex is used as a catalyst. The copper complex in poly(l-vinylimidazole-co-vinylpyrrolidone) has been found [38] to act as an excellent catalyst and to exhibit the highest activity for melanin formation. The ratio of the rate constants ( m/ d) is approximately 3 (tyrosinase... 

The polymerization of compounds having active methyne groups has also been reported [81] (Eq. 8). The oxidative coupling polymerization of these monomers follows a mechanism similar to that of phenols. The catalytic cycle observed in the polymerization of / -phcnylcncdiaminc with Fe(edta) as the catalyst in an aqueous solution differs from that in the polymerization of phenols as follows The activation of monomers usually involves either electron transfer from the anion or elimination of a hydrogen atom from the monomer. The oxidative polymerization of phenols uses the former mechanism of the electron transfer. In contrast, in the case of the polymerization of aromatic diamines as monomers, the neutral amines are coordinated to the catalyst, followed by the subsequent electron transfer and dehydronation. The dehydronation proceeds by the reaction with 02. Another mechanism has also been proposed where dehydrogenation... 

Asymmetric oxidative coupling polymerization of hydroxynaphthalene derivatives was investigated by Habaue and Okamoto et al. First, they studied the oxidative coupling polymerization of optically active 3,3/-hydroxy-2,2/-dimethoxy-1,1 -binaphthalene with copper catalysts bearing chiral ligands under an oxygen atmosphere (Scheme 41) [166]. The obtained polymers had molecular weights of 3100-5200. When the polymerization of (J )-monomer... 

The poly(3, 4 -alkylterthiophene), PTT (2) used in our studies is prepared by FeCl3-mediated oxidative coupling polymerization [39]. PTT with a long alkyl side-chain (R > C6) for example PTT-10 (2, R = n-Ci0H2i) has an ability to self-organize in the solid state as reflected by a bathochromic shift in its UV-visible absorption spectra from solution to thin film (Fig. 4.1a). The solution spectrum of PTT-10 also has a progressive bathochromic shift with concomitant appearance of a longer-... 

The telechelica,(i -bis(2,6-dimethylphenol)-poly(2,6-dimethylphenyl-ene oxide) (PP0-20H) [174-182] is of interest as a precursor in the synthesis of block copolymers [175] and thermally reactive oligomers [179]. The synthesis has been accomplished by five methods. The first synthetic method was the reaction of a low molecular weight PPO with one phenol chain end with 3,3, 5,5 -tetramethyl-l,4-diphenoquinone. This reaction occurred by a radical mechanism [174]. The second method was the electrophilic condensation of the phenyl chain ends of two PPO-OH molecules with formaldehyde [177,178], The third method consists of the oxidative copolymerization of 2,6-dimethylphenol with 2,2 -di(4-hydroxy-3,5-di-methylphenyl)propane [176-178]. This reaction proceeds by a radical mechanism. A fourth method was the phase transfer-catalyzed polymerization of 4-bromo-2,6-dimethylphenol in the presence of 2,2-di(4-hy-droxy-3,5-dimethylphenyl)propane [181]. This reaction proceeded by a radical-anion mechanism. The fifth method developed was the oxidative coupling polymerization of 2,6-dimethylphenol (DMP) in the presence of tetramethyl bisphenol-A (TMBPA) [Eq. (57)] [182],... 

Imidazole copper(II) complexes had previously functioned as catalysts in the oxidative coupling polymerization of DMP [183-186]. The mechanism which was proposed for this reaction involved the participa-... 

PPE is the generic name for the homopolymer, poly(2,6-dimethyl,l,4-phenylene ether) derived from the oxidative coupling polymerization of... 

Since the discovery of PPO by Allan S. Hay ofthe General Electric Company in the 1960s [3,41], over 1500 patents have been issued in the field of oxidative coupling polymerization, and the total sales worldwide of engineering plastics based on PPO to date represent about US 1 billion per year. In fact, Noryl -modrfied PPO resins have become the world s most successful and best-known polymer blends and alloys. 

Oxidative coupling polymerization in SCCO2 has been demonstrated for the synthesis of poly(2,6-dimethylphenylene oxide) 27. The polymerization of 2,6-dimethylphenol in the presence of oxygen is conducted using CuBr as the catalyst, pyridine and a block copolymer of styrene and 1,1-dihydroperfluorooctyl acrylate (PS- -PFOA) as a stabilizer in SCCO2 (350 bar) at 40 C. The polymerization occurred via a dispersion process and produced the polymer in a 74% yield with high molecular weight (17 000) (Scheme 46). 

Starting from an optically active dimer, tetramer, or octamer of 2,3-dihy-droxynaphthalene derivatives, Tsubaki and co-workers realized the synthesis of numerous optically active oligonaphthalene products by second-order asymmetric transformation under amine-copper conditions (Scheme 3.17). On the other hand, Okamoto and co-workers achieved asymmetric oxidative coupling polymerization (AOCP) reactions to synthesize poly(2,3-dihy-droxy-l,4-naphthylene) derivatives (Scheme 3.18). The starting materials of AOCP reactions can be either partially protected tetrahydroxybinaphthale-nes or 2,3-dihydroxynaphthalene. The chiral Cu complexes ligated by (-)-sparteine or bisoxazolines were identified as suitable catalysts for these reactions. However, the enantioselectivity attained in these AOCP reactions was estimated to be low. 

Based on the above achievements, the group of Habaue systematically studied Cu-catalyzed asymmetric oxidative coupling polymerization reactions. 

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