Phosgene, polycondensation with

Polycondensation of Bisphenols, II, with Phosgene. Polycondensation of siloxane-linked bisphenols, II, with phosgene is the most obvious synthetic approach leading to siloxane-modified poly(arylene carbonates) since the phosgene-bisphenol polycondensation is used in the synthesis of aromatic polycarbonates (1). This method was used initially to prepare polymer (as indicated in reaction 1) as well as for the attempted synthesis of polymers 2 and 5 ... 

Originally, polycarbonate was produced by interfacial (organic/aqueous) polycondensation of phosgene (COClj) with disodium salt of a bisphenol, such as 2,2-bis(4-hydroxyphenyl)propane (bisphenol A or BPA). Initially, the reaction produces an intermediate chloroformate R0C(0)C1 (Eq. (12.1)), which subsequently reacts with another phenoxide molecule, growing a polymer chain... 

When bisphenol-C was polycondensed with IPCl either in homogeneous solution or in a biphasic system, the same trends were observed. The maximum molar masses and the difference between homogeneous and interfacial polycondensations were smaller [12] The lower Mn values compared to a phosgenation are a consequence of the fact that hydrolysis of a carboxylic acid chloride group is a irreversible termination step, whereas a loss of phosgene or chloroformiate groups may be compensated for by an excess of phosgene. 

Phosgene addition is continued until all the phenoHc groups are converted to carbonate functionahties. Some hydrolysis of phosgene to sodium carbonate occurs incidentally. When the reaction is complete, the methylene chloride solution of polymer is washed first with acid to remove residual base and amine, then with water. To complete the process, the aqueous sodium chloride stream can be reclaimed in a chlor-alkah plant, ultimately regenerating phosgene. Many variations of this polycarbonate process have been patented, including use of many different types of catalysts, continuous or semicontinuous processes, methods which rely on formation of bischloroformate oligomers followed by polycondensation, etc. 

Tough, transparent, heat and flame resistant, multiblock (bisphenol fluorenone carbonate) (BPF)-dimethylsiloxane copolymers have been synthesized by interfacial polycondensation of phosgene with various mixtures of BPF end-capped siloxane oligomers and free BPF or its monosodium salt 232). Siloxane content of the copolymers were varied between 7 and 27%. Presence of two Tg s, one below —100 °C and the other as high as 275 °C, showed the formation of two-phase morphologies. 

Polycarbonates have also been studied recently with regard to chemical heterogeneity. Polycarbonates are polycondensation products of phosgene and aliphatic or aromatic dihydroxy compounds. 

Aromatic polycarbonates are currently manufactured either by the interfacial polycondensation of the sodium salt of diphenols such as bisphenol A with phosgene (Reaction 1, Scheme 22) or by transesterification of diphenyl carbonate (DPC) with diphenols in the presence of homogeneous catalysts (Reaction 2, Scheme 22). DPC is made by the oxidative carbonylation of dimethyl carbonate. If DPC can be made from cyclic carbonates by transesterification with solid catalysts, then an environmentally friendlier route to polycarbonates using C02 (instead of COCl2/CO) can be established. Transesterifications are catalyzed by a variety of materials K2C03, KOH, Mg-containing smectites, and oxides supported on silica (250). Recently, Ma et al. (251) reported the transesterification of dimethyl oxalate with phenol catalyzed by Sn-TS-1 samples calcined at various temperatures. The activity was related to the weak Lewis acidity of Sn-TS-1 (251). 

The reaction between a dihydroxy compound (bisphenol) and phosgene, which is performed on an industrial scale, proceeds even at room temperature.The reaction is generally carried out in a biphasic medium consisting of methylene chloride (with dissolved phosgene) and aqueous sodium hydroxide (with dissolved bisphenol sodium salt) and a phase transfer catalyst (e.g.triethylamine).The procedure is termed interfacial polycondensation (see Sect.4.1.2.3 and Examples 4-5,4-12,and 4-13). 

Homopolycarbonates based on 1 and 2 have been prepared by several groups. The interfacial polycondensation typical for the synthesis of aromatic polycarbonates is not useful with alditols, including 1, because they are water-soluble and less acidic than diphenols. The 1-based homopolycarbonate was prepared by phosgena-tion of the sugar diol, with phosgene or diphosgene in pyridine-containing solvent mixtures at low temperatures. The polycondensation of the isosorbide bischloro-formate in pyridine is an alternative approach. 

Polycarbonates are amorphous polymers with excellent handling properties. Their spectrum of applications ranges from baby bottles to compact discs. Most of the polycarbonate produced is generated by the polycondensation of bisphenol A with phosgene in a biphasic system (sodium hydroxide/dichloromethane). The solution of the polycarbonate product in dichloromethane is washed with water to remove the by-product NaCl. However, in this washing process some 20 g L 1 of the dichloromethane ends up dissolved in the aqueous phase. The dichloromethane must also be removed from the polycarbonate, which is not easy. This means that the polycarbonate will invariably contain some chlorinated impurities, which adversely affects the properties of the polymer. 

Green chemistry offers the scientific option to deal with the problems associated with hazardous substances. An example is the alternative synthesis of polycarbonate, a polymer that has been commercially produced by the polycondensation between bisphenol-A and phosgene. The traditional synthesis is shown in Figure 12.2. Because phosgene is highly poisonous, a safer option is to use diphenyl carbonate as a non-toxic carbonylation reagent. See Figure 12.3 (Anastas and Williamson, 1996). 

Some polysulfides contain in the polymer backbone other groups besides -S-. A common type of group is oxycarbonyloxy, such as in the polymer resulting from the reaction of phosgene (chloroformyl chloride or carbonic acid dichloride) with 4,4 -thiobisphenol. This reaction can be considered a polycondensation and can be written as follows ... 

Polycarbonate resins are important engineering thermoplastics with good mechanical and optical properties as well as electrical and heat resistance, useful for many engineering applications. Polycarbonates have been commercially produced by the interfacial polycondensation between a bisphenol-A salt in an aqueous caustic solution and phosgene in an organic solution as follows [reaction (13)] ... 

Since the successful use of phenylphosphiiK dichloride 2 [11], hexachloro-cyclotriphosphatriazene 3 [12], triphenylphosphine 4 [13] and diphenylchloro-phosphate 5 [14] in the synthesis of polyesters, Ogata et al. studied direct polycondensation of diacid and diamii in the presence of triphenylphosphine dicMoride (TPPCI2) [15b] which can form in situ when triphenylphosphine is treated with hexachloroethane or when triphenylphosphine oxide interacts with phosgene or oxalyl chloride (Scheme 3) [15a],... 

One of the advantages of this approach is the possibility of reconverting the by-product triphenylphosphine oxide to TPPClj by treating it with more oxalyl chloride or phosgene. During the polycondensation reaction, theTPPCl2, which exists in form of an ion pair, reacts with diacid to form the activated intermediate 6 in the presence of pyridine, which in turn reacts with the diamim to form the polymer (Scheme 4) [15a]. 

Polycarbonates are characterized by the carbonate (-0-COO-) interunit linkage. They may be prepared by interfacial polycondensation of bisphenol A and phosgene in methylene chloride-water mixture. The resulting hydrogen chloride is removed with sodium hydroxide or, in the case of solution polymerization, pyridine is used as the hydrogen chloride scavenger. Polycarbonate may also be made by ester interchange between bisphenol A and diphenyl carbonate. 

This polymer can be prepared by the interfacial polycondensation of bisphenol A alkali salt dissolved in the water phase and phosgene (COQj) dissolved in methylene chloride. It can be used either as the pure polymer or in blends, particularly with acrylonitrile-butadiene-styrene (ABS) copolymers. The bisphenol A structure appears in other combinations, e.g., in a polysulfone copolymer (see Table 15.10) and in aromatic polyesters with phthalic acid moieties... 

The polyarylesterketones can be produced by means of interaction between bisphenylsulfide, dibenzo rane and bisphenyloxide with monomers of electrophylic nature (phosgene, terephthaloylchloride) or using homopolycondensation of 4-phenoxybenzoylchloride and 4-phenoxy-4-chlorcarbonyl-bisphenyl in the presence of dichloroethane at 25 °C [282-285], Aromatic polyesterketones form after the polycondensation of 4-phenoxybenzoylchloride with chloranhydrides of tere- and isophthalic acids, 4,4 -dicarboxybisphenyloxide in the environment of nitrobenzene, methylchloride and dichloroethane at temperatures from -70 till 40 °C during 16-26 h according Friedel-Crafts reaction. 

When, for example, piperazine, ethylene glycol, phosgene, and adipyl dichloride are simultaneously polycondensed, a copolymer with a more or less random distribution of monomeric units is produced. In this case, however, the sequence of monomeric units is still regulated by the fact that a B monomeric unit (carbonic acid or adipic acid) can only be followed by an A monomeric unit (piperazine or ethylene glycol). 

With a few exceptions, interfacial polycondensation has remained a laboratory method for the synthesis of polymers, since diacyl chlorides are too expensive for commercial production. The exceptions include the polycondensation of bisphenols with phosgene (see Section 26.5.1) and the synthesis of aromatic polyamides, from m-phenylene diamine, isophthaloyl chloride, and terephthaloyl chloride (Section 28.2.4). The method is also used to give wool a fluff-free finish by producing a polycondensate from sebacoyl chloride and hexamethylene diamine on the wool fiber. 

The polycondensation of a diol and the diester of a dicarboxylic acid (e.g., the dimethyl ester) can be carried out in the melt at a considerably lower temperature than for the corresponding reaction of the free acid. Under the influence of acidic or basic catalysts a transesterification occurs with the elimination of the readily volatile alcohol (see Example 4.3). Instead of diesters of carboxylic acids one can also use their dicarboxylic acid chlorides, for example, in the synthesis of high-melting aromatic polyesters from terephthaloyl dichloride and bisphenols. The commercially very important polycarbonates are obtained from bisphenols and phosgene, although the use of diphenyl carbonate as an alternative component is of increasing interest (see Example 4.4). Instead of free acids, cyclic carboxylic... 

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