Dihalide monomers

TABLE 6.2 Dihalide Monomers Modified with Functional Groups... 

Difluoro monomers, 341 Difunctional monomers, 12 Dihalide monomers, modified with functional groups, 357 Dihalides, activated, 346, 356-359 Dihydroxybenzophenone (DHBP), 342-343, 420... 

The remaining polymerization route involves zero-valent nickel complexes and dihalide monomers. Variations of this route most often arise where different sources or regeneration methods of the active nickel species are utilized [82,199, 200-204]. A typical example is shown below in Scheme 51 in which poly(3-phe-nylthiophene) 50 is synthesized from the parent 2,5-dichlorothiophene. As with the Ullmann reaction, polymerization appears to be most compatible with ring systems containing electron-withdrawing substituents. 

And also, conjugated polymers can be prepared through Heck s coupling between dihalide monomer and divinylbenzene monomer. This coupling reaction is very useful when the synthesis of dialdehyde monomer and bissulfonium or bisphosphonium salt monomer is difficult or impossible. But Heck s coupling has a problem in that very often the preparation of divinylbenzene monomers is... 

Yu and coworkers describe a technique to retain stability and maximize the electrooptic response. They preformed the imide structure with an aryl dihalide monomer and incorporated highly efficient chromophore groups before polymerization. This highly functionalized monomer was subjected to a Pd-catalyzed coupling reaction with 2,5-bis(tributyltin)thiophene to give the polymer... 

The nature of R in dihalide monomers can vary, but usually primary, saturated, or unsaturated aliphatic dihalides are employed since the secondary and tertiary type mainly undergo dehydrohalogenation [4],... 

To obtain good elastomers (thiokol rubbers) the dihalide monomer must have four or more methylene groups. 

Their drawback is that they demonstrate low tensile strength and abrasion resistance. They also release disagreeable odor during processing. Concentration of the odor increases as the number of carbon atoms of the dihalide monomer decreases. 

Donald KJ, Hoffmann R (2006) Solid memory structural preferences in group 2 dihalide monomers, dimers, and solids. J Am Chem Soc 128 11236-11249... 

The synthesis of linear polymer is accompanied by the formation of cyclics. The amount and structure of cyclics depends on the amount and structure of dihalide monomer Cl—R—Cl in the following order [7] ... 

The polysulfide polymers are prepared as a suspension by condensation of the dihalide monomer with polysulfide in aqueous solution [18]. Bis-2-dichloro-ethyl formal is the monomer usually used, and 0.1-0.4% 1,2,3-trichloropropane is added as a crosslinking monomer [19]. In conducting polymerization, the standard practice is to feed the dihalide monomer into the aqueous polysulfide solution containing specific suspending and nucleating agents. A combination of an alkyl naphthalene sulfonate with magnesium hydroxide sol prepared in situ is commonly used. 

Use of a mixed dihalide monomer feed in a conventional polymerization will produce random copolymers. A block copolymer cannot be prepared by a stepwise addition of the monomers. During copolymerization interchange takes place, resulting in randomization. To prepare block copolymers, it is best to prepare individual mercaptan-terminated polymers, blend them in the desired proportion, and then process the blended system by conventional techniques. 

As in the other polycondensation reactions, competition between linear polymerization and ring formation also occurs here and it is strongly dependent on the structure of both the dihalide and inor nic polysulfide. CycUc monosulfides are favoured when the dihalide monomer has four or five carbon atoms between the halide terminals [18]. 

The structural determination of the polymers was made by NMR. The integration and appropriate analysis of known reference protons of the polymers enabled the relative compositions of the various polymers to be determined. The protons adjacent to the sulfonated group derived from the disulfonated dihalide monomer in the polymers were well separated from the other aromatic protons (8.25 ppm). Figure 6.8 shows NMR spectrum of the SPTES-100 homopolymer. 

The sulfonation of the dihalide monomer has the advantage that the deactivated ring in orf/zo-position to the halogen is sulfonated, giving rise to higher stability with... 

Yang J, Gibson HW (1999) A polyketone synthesis involving nucleophilic substitution via carbanions derived from bis(a-aminonitrile)s. 5. A new, well-controlled route to long bisphenol and activated aromatic dihalide monomers. Macromolecules 32 8740-8746... 

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