Phase transfer polymerization mechanism

Fig. 6. Phase-transfer polymerization mechanism between bisphenols and 1,6-dibromohexane in H20/nitrobenzence mixture.

In conclusion, phase transfer catalyzed Williamson etherification and Wittig vinylation provided convenient methods for the synthesis of polyaromatics with terminal or pendant styrene-type vinyl groups. Both these polyaromatics appear to be a very promising class of thermally reactive oligomers which can be used to tailor the physical properties of the thermally obtained networks. Research is in progress in order to further elucidate the thermal polymerization mechanism and to exploit the thermodynamic reversibility of this curing reaction. 

Although the lariat ethers (29-31) were conceived on principles related to biological activity, they are interesting candidates for study as either free phase transfer catalysts, or as polymer-bound catalysts. In the latter case, the sidearm could serve both a complexing function and as a mechanical link between macroring and polymer. Polymeric phase transfer catalyst systems have been prepared... 

The kinetics of methyl methacrylate (MMA) polymerization in ethyl acetate/water two phase systems was described as being more well-behaved ( ). Using hexadecylpyridinium chloride (HPC) as the phase transfer catalyst, Rp was found to be approximately first order in MMA concentration. In support of a typical phase transfer mechanism, it was found that... 

Functionalized polymers are of interest in a variety of applications including but not limited to fire retardants, selective sorption resins, chromatography media, controlled release devices and phase transfer catalysts. This research has been conducted in an effort to functionalize a polymer with a variety of different reactive sites for use in membrane applications. These membranes are to be used for the specific separation and removal of metal ions of interest. A porous support was used to obtain membranes of a specified thickness with the desired mechanical stability. The monomer employed in this study was vinylbenzyl chloride, and it was lightly crosslinked with divinylbenzene in a photopolymerization. Specific ligands incorporated into the membrane film include dimethyl phosphonate esters, isopropyl phosphonate esters, phosphonic acid, and triethyl ammonium chloride groups. Most of the functionalization reactions were conducted with the solid membrane and liquid reactants, however, the vinylbenzyl chloride monomer was transformed to vinylbenzyl triethyl ammonium chloride prior to polymerization in some cases. The reaction conditions and analysis tools for uniformly derivatizing the crosslinked vinylbenzyl chloride / divinyl benzene films are presented in detail. 

An Sjuyl-type (S l ) mechanism has been proposed in the synthesis of poly(2,6-dimethyl-l,4-phenylene ether) through the anion-radical polymerization of 4-bromo-2,6-dimethylphenoxide ions (204) under phase-transfer catalysed conditions269. Ions 204 are oxidized to give an oxygen radical 205. The propagation consists of the radical nucleophilic substitution by 205 at the ipso position of the bromine in 204 (equation 144). The anion-radical 206 thus formed eliminates a bromide ion to form a dimer phenoxy radical 207 (equation 145). A polymeric phenoxy radical results by continuation of this radical nucleophilic substitution. 

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],... 

Many operations in chemical engineering require the contact of two liquid phases between which mass and heat transfer with reaction occurs. Examples are hydrometallurgical solvent extraction, nitrations and halogenations of hydrocarbons, hydrodesulfurization of crude stocks, emulsion polymerizations, hydrocarbon fermentations for single-cell proteins, glycerolysis of fats, and phase-transfer catalytic reactions. A most common method of bringing about the contact of the two phases is to disperse droplets of one within the other by mechanical agitation. 

It has been demonstrated that 2,5-bis-(chloromethyl)-l,3,4-oxadiazole can undergo anionic polymerization. With sodium alcoholate, poly(l,3,4-oxa-diazole-2,5-diyl-l,2-vinylene) is formed, however the reaction cannot be controlled even at temperatures as low as —40°C. Instead, the exothermic reaction can be controlled by performing the polymerization at a toluene/ water interface with tetrabutylphosphonium bromide as a phase transfer catalyst. The mechanism is shown in Figure 10.7. 

Results obtained by Brillouin scattering range from the determination of the elastic and photoelastic constants of materials to the analysis of material transformations phase transitions, polymerization, glass transitions, pho-toinduced transformations, etc. (It is out of the scope of this presentation to present all.) We will limit our discussion to some examples selected in the field of supramolecular products defined as complexes consisting of two or more chemical entities associated through van der Waals interactions, hydrogen bonds, or charge-transfer mechanisms. " ... 

Interfacial polymerization process. The interfacial polymerization process is the oldest and most widely used of the commercial processes. Although different companies and even different manufacturing plants may have variations of the interfacial process, overall they are quite similar. Both batch and continuous interfacial processes have been practiced. The overall reaction (shown below in Fig. 14.1) involves the condensation of BPA with phosgene. A base, typically caustic, is used to scavenge the hydrochloric acid generated. The condensation is catalyzed with a tertiary amine and/or a phase transfer catalyst or both. The condensation is done in a two-phase medium such as methylene chloride and water. For a more in-depth discussion of the reaction mechanism, the reader is referred to the following sources [50—58]. 

Applications of Crown Ethers.—Crown ethers have been found to form molecular complexes with bromine that can be used as reagents in bromination reactions, e.g. of alkenes. The crown-halogen interaction seems not to be encapsulation but rather to be the formation of a polymeric structure. The complexes of nitro-nium tetrafluoroborate (NO2BF4) with various crown ethers, for example the 1 1 complex with 18-crown-6, have been reported to be selective nitrating agents. A new rapid synthesis of alkylseleno- and alkyltelluro-arenes from arenediazon-ium tetrafluoroborates and dialkyl diselenides or ditellurides employs KOAc and 18-crown-6 as a phase-transfer catalyst a radical mechanism has been suggested. Fluorine-19 n.m.r. evidence has been presented to show that KF forms... 

The presence of radical byproducts such as Cl radicals and the formation of unsaturated and defect structures in PVC point to a complex polymerization mechanism. The partitioning of the volatible radicals (monomeric. Cl,..) between vapor, water and polymer particles may vary the radical concentration in particles and the aqueous phase. Exit of radicals from the particles and the aqueous phase to the vapor phase probably negatively influences the growth events in the system. The low concentration of monomer in the vapor phase favors more termination. The decrease of the chain transfer to monomer with decreasing reactor pressure (at subsaturation pressures) favors the hypothesis that the volatile radicals exit to the vapor phase. The chain transfer is constant at saturation pressure and decreases with increasing pressure at subsaturation conditions. 

Phase-transfer catalysis (PTC) has been recently applied to the preparation of polyethers by polycondensation 1 1. This method offers several advantages over solution conducted nucleophilic displacement step-growth polymerizations. These include the substitution of inexpensive solvents for anhydrous aprotic solvents such as DMSO, DMAC etc. .., lower reaction temperatures and shorter reaction times. We wish to report our results concerning the preparation of polyethers from bisphenol A (BPA) and 1,4-dichloro-2-butene (DCB) under PTC conditions. The kinetics and the mechanism of this new type of polycondensation are described. 

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