Nucleophilic displacement polymerization reaction

The nucleophilic displacement polymerization reaction is more common for the synthesis of PAEs because of the easy accessibility of monomers and high yield of high-molecular-weight polymers. Nucleophilic displacement of an activated dihalo or dinitro compound with an activated bisphenol (mostly in the form of bisphenoxides) at high temperatures has been the most common method of PAE synthesis [35,37,39], The reaction is conducted in solution using different otic solvents, for example, V-methyl-2-pyrrolidone (NMP), V,V-dimethyl acetamide (DMAc), or dimethyl sulfoxide (DMSO). 

Recently, the above mentioned model reaction has been extended to polycondensation reactions for synthesis of polyethers and polysulfides [7,81]. In recent reports crown ether catalysts have mostly been used in the reaction of a bifunctional nucleophile with a bifunctional electrophile, as well as in the monomer species carrying both types of functional groups [7]. Table 5 describes the syntheses of aromatic polyethers by the nucleophilic displacement polymerization using PTC. 

The syntheses of iron isonitrile complexes and the reactions of these complexes are reviewed. Nucleophilic reagents polymerize iron isonitrile complexes, displace the isonitrile ligand from the complex, or are alkylated by the complexes. Nitration, sulfonation, alkylation, and bromina-tion of the aromatic rings in a benzyl isonitrile complex are very rapid and the substituent is introduced mainly in the para position. The cyano group in cyanopentakis(benzyl isonitrile)-iron(ll) bromide exhibits a weak "trans" effect-With formaldehyde in sulfuric acid, benzyl isonitrile complexes yield polymeric compositions. One such composition contains an ethane linkage, suggesting dimerization of the transitory benzyl radicals. Measurements of the conductivities of benzyl isonitrile iron complexes indicate a wide range of A f (1.26 e.v.) and o-o (1023 ohm-1 cm.—1) but no definite relationship between the reactivities of these complexes and their conductivities. 

An AB monomer, 2-(4-hydroxyphenyl)-3-phenyl-6-fluoroquinoxaline [17], was prepared from the reaction of 4-hydroxybenzil and l,2-diamino-4-fluorobenzene and subsequently polymerized under aromatic nucleophilic displacement conditions in NMP. The resultant polymer exhibited an intrinsic viscosity of 1.23 dL/g, a Tg of 247 °C and thin film tensile strength and modulus at room temperature of 107 Mpa and 3.2 GPa, respectively [17]. The same AB monomer was also copolymerized with hydroquinone and 4,4 -difluorodiphenyl sulfone to yield a series of copolymers with interesting properties [17]. The same AB monomer was prepared and polymerized by other researchers to yield a polymer with an intrinsic viscosity of 0.65 dL/g and a Tg of 255 °C [18]. 

Diazotization in the presence of boron trifluoride enables diazonium tetrafluoroborates to be isolated from the reaction mixture and purified. Subsequent controlled decomposition produces the required fluoroaromatic. Although explosion hazards and the toxicity of the isolated salts are significant concerns with this process, known as the Balz-Schiemann process, 4,4 -di-fluorobenzophenone (BDF. 6) has been prepared by this route as a monomer for the production of the engineering plastic poly(ether ether ketone) , or PEEK , by condensation with 1,4-dihydroxybenzene in the presence of potassium carbonate. BDF 6 is superior to its chlorine analog because in aromatic systems the nucleophilic displacement of fluorine is more facile than that of chlorine, leading to a shorter polymerization time and a better quality product containing less degradation impurities. 

Thus, owing to their tendency toward polymerization and the difficulties often encountered in their preparation, systematic investigation of the chemistry of epiBulfvdea have been rate indeed. The nucleophilic displacement reactions reviewed in this section are often by necessity related to specific examples. Generalization of a given reaction should be viewed Cautiously until more detailed investigations are reported. 

Thus polystyryl carbanions and polyacrylonitrile carbanions prepared by anionic polymerization were reacted with cellulose acetate or tosylated cellulose acetate in tetrahydrofuran under homogenous reaction conditions. The carbanions displaced the acetate groups or the tosylate groups in a S v2-type nucleophilic displacement reaction to give CA-g-PS and CA-g-PAN. Mild hydrolysis to remove the acetate/tosylate groups furnishes the pure cellulose-g-polystyrene (Figure 3). 

The macromolecular silyl chloride reacts with sodium in a two-electron-transfer reaction to form macromolecular silyl anion. The two-electron-trans-fer process consists of two (or three) discrete steps formation of radical anion, precipitation of sodium chloride and generation of the macromolecular silyl radical (whose presence was proved by trapping experiments), and the very rapid second electron transfer, that is, reduction to the macromolecular silyl anion. Some preliminary kinetic results indicate that the monomer is consumed with an internal first-order-reaction rate. This result supports the theory that a monomer participates in the rate-limiting step. Thus, the slowest step should be a nucleophilic displacement at a monomer by macromolecular silyl anion. This anion will react faster with the more electrophilic dichlorosilane than with a macromolecular silyl chloride. Therefore, polymerization would resemble a chain growth process with a slow initiation step and a rapid multistep propagation (the first and rate-limiting step is the reaction of an anion with degree of polymerization n[DP ] to form macromolecular silyl chloride [DP +J, and the chloride is reduced subsequently to the anion). 

This is an example of the preparation of ABA-type thermoplastic elastomer. Styrene is polymerized first since styryl initiation of isoprene is faster than the reverse reaction. The reaction is carried out in a nonpolar solvent with Li" " as the counterion to enable predominantly cis-l,4-polyisoprene to be formed in the second growth stage. The living polystyrene-6/ocfc-polyisoprene AB di-block copolymer resulting from the second stage is then coupled by a double nucleophilic displacement of Cl ions from a stoichiometric equivalent of dichloromethane to give a polystyrene-61ock-polyisoprene-/)/ock-polystyrene triblock copolymer. 

Cross-Linking Reactions of Polymers. Bisdichloromaleimide-amine polymers contain (a) a double bond in the maleimidyl group, (b) chlorine, and (c) secondary amine group (-NH-). It may be possible to cross-link them either by the opening of the double bond (thermal polymerization) or by the nucleophilic displacement of chlorine by the secondary amine. The representative reaction scheme for such reactions is shown in Figure 6. The extent of such reactions may be evaluated by solubility measurements in dimethyIformamide. 

Hydrolysis and condensation occur by bimolecular nucleophilic displacement reactions involving OH and Si-0 anions. For w > 4, the hydrolysis of all polymeric species is expected to be complete. Dissolution reactions provide a continual source of monomers. Because condensation occurs preferentially between weakly acidic species that tend to be protonated and strongly acidic species that are deprotonated, growth occurs primarily by reaction-limited monomer-cluster aggregation (equivalent to nucleation and growth), leading to compact, nonfractal structures. 

The basic reaction in the polymerization process is a nucleophilic displacement of halide by polysulphide anion, e.g., with disulphide ... 

It was also of interest to examine the polymerization of monomer 11 via nucleophilic displacement of the chloro groups with oxygen- and sulfiu-based nucleophiles. Our previous studies have shown that fliese reactions proceed under nuld reaction conditions to yield soluble polycationic organoiron polymers. " Scheme 5 shows the reaction of 11 with 14a and 14b to produce polymers 15a and 15b. 

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