Condensation polymerization, catalyzed transfer

Aromatic Substitution in Condensation Polymerization Catalyzed by Solid-Liquid Phase Transfer... 

A quite different approach to chain-growth condensation polymerization is phase-transfer-catalyzed polycondensation of solid monomer dispersed in an... 

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... 

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]. 

An important industrial reaction and one of the earliest applications of phase transfer catalysis by quaternary ammonium salts is the synthesis of polycarbonates [13]. Typically, 2,2-(4,4 -dihydroxydiphenyl)propane(bisphenol A) is dissolved in concentrated aqueous sodium hydroxide and exposed to a dichloromethane solution of phosgene. Salts such as benzyltriethylammonium chloride or tertiary amines catalyze the condensation polymerization [13—18]. The two phase polymerization is formulated in equation 6.6. 

After reaching the desired DP, 40-50 % of the oligomeric melt is transferred to the polymerization vessel. Titanium butoxide (50-150 ppm) or dibutyl tin oxide catalyst (100-250 ppm), or some combinations of the two catalysts, is added to catalyze polymerization at 260-275 °C. A vacuum of <0.15 kPa is applied to remove the condensed water so as to drive the reaction until the polymer reaches an intrinsic viscosity (IV) of 0.7-0.9 dL/g. 

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],... 

Other metal-catalyzed reactions with five-membered pincers include asymmetric aldol-type condensations [26, 28-30], cyclopropanations [31], enantioselective allylations [32], reductive eUminations [33], transfer hydrogenations [28-30, 34], hydroaminations [28], and polymerizations [26, 28, 35]. 

Direct esterification of PDO with TPA is the preferred commercial route to polymerize PTT because it is more economical than using DMT. Figure 1 shows the reaction scheme. Because TPA has a melting point > 300°C and has poor solubility in PDO, esterification is carried out in the presence of a heel and imder a pressure of 70-150 kPa at 250-270°C for 100-140 min. Heel is an oligomeric PTT melt with a degree of polymerization (DP) of 3-7 purposely left in the reaction vessel from a previous reaction to act as a reaction medium and to increase TPA solubility. The esterification step is self-catalyzed by TPA. After reaching a DP of about 3-7, 40-50% of the oligomers is transferred to the polymerization vessel. Titanium butoxide or dibutyl tin oxide catalyst (50-150 ppm) is added to initiate polymerization at 260-275°C. Vacuum (<0.15 kPa) is applied to remove the condensed water until the polymer reaches an intrinsic viscosity (IV) of 0.7-0.9 dL/g. 

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