Polyetherification phase transfer catalyzed

The thermotropic aromatic main chain liquid crystalline polymers are also prepared by the phase transfer catalyzed aromatic nucleophilic polymerization [87]. Polyetherification of bis(4-chloro-3-nitrophenyl) sulfone with mesogenic aromatic diols is shown below ... 

Several particularities of phase transfer catalyzed polyetherification are as follows. Stoichiometric phase transfer catalyzed pol)rmerizations do not take place between stoichiometric ratio of monomers, since the nucleophilic monomer is always transferred in a small amount into the organic phase. Consequently, because their reaction is a non-stoichiometric one there is no need for an equimolar ratio between the two monomers to get polymers with high molecular weights. High molecular weight polymers are usually obtained also at low conversions. In several cases, even at 100 percent conversion the polydispersity of the obtained polymers is low, i.e., "Hw/Hh 1.3. At any conversion, the organic phase contains only pol3rmers with electrophilic chain ends, even when the nucleophilic monomer was used in excess. 

All these particularities of phase transfer catalyzed polyetherification were staying behind our approach to the design of new macromolecules. 

Recently we have developed a new class of thermotropic liquid crystalline (LC) main-chain pol3rmers, i.e., polyethers of mesogenic bis-phenols(16-17.23-26). Since the obtained polymers are not soluble in dipolar aprotic solvents, the only available synthetic avenue for their preparation consists in the phase transfer catalyzed polyetherification. 

Percec and Rodenhouse presented the first main-chain liquid crystalline polymer with a crown ether moiety in the backbone of the polymer [83], Liquid crystalline polyethers 63 were obtained by phase transfer catalyzed polyetherification of... 

Polymer Synthesis. The polymers were made by a phase-transfer-catalyzed Williamson ether synthesis as described in the literature (15-201. and one reason for this choice of polyetherification method was that only electrophilic chain ends are produced (15.20-221. which gives the polymer a well-defined structure. This was important for die transition kinetics measurements presented later in this paper. 

Figure 6. Synthesis of LC polyethersby a phase transfer catalyzed polyetherification reaction.

Polyethers are usually prepared by a phase transfer catalyzed polyetherification reaction between the sodium salt of the meso-genic diphenol dissolved in water and an a,o>-dibromoalkane dissolved in o-dichlor-obenzene or nitrobenzene in the presence of... 

Conventional liquid-liquid two-phase (organic solvent-50% NaOH aqueous solution) phase transfer catalyzed polyetherification reaction conditions were used for the preparation of both the polyfonnal and polyethers reported in Table 1. The polymerizations were carried out at 70 C in o-dichloro-benzene- 50% NaOH water solution (10 times mole excess NaOH vs phenol groups), in the presence of tetrabutylammonium hydrogen sulfate (TBAH) as phase transfer catalyst. A typical example is presented below. HMS,... 

The experimental results on the synthesis and characterization of PHMS are summarized in Table 1. Only 1,2-dibromoethane did not produce any polymer, and comments on this result will be reserved until later. As we have speculated, all the obtained polyethers are soluble in organic solvents like o-dichlorobenzene, THF and CHCl (Table 1). These are conventional solvents for further functionalization of the a,o)-dielectrophilic oligomer s chain ends, or for the preparation of alternating or triblock copol3nners by phase transfer catalysed polyetherification. Conversely, the polyethers are not soluble in dipolar aprotlc solvents. As a result, conventional condensation polymerization reactions can not be used for their synthesis. The only available synthetic procedure to be used for their preparation is phase transfer catalyzed polyetherification. The polyethers containing an... 

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