Interfacial polycondensation polycarbonates

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). 

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. 

Interfacial polycondensations can also be carried out in vapor-liquid systems. Reaction takes place at the interface between an aqueous solution of a bifunctional active hydrogen compound and the vapor of diacid chloride. Interfacial condensation is commercially important in the synthesis of polycarbonates (1-52). Polymerizations based on diacids are always less expensive than those that use diacid chlorides. In the polycarbonate case, however, the parent reactant, carbonic acid, is not suitable and the derived acid chloride, phosgene (COCI2), must be used. 

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)] ... 

Dobkowski, Z. Weilgosz, Z. Krajewski, B. Molecular weight control of polycarbonates obtained by interfacial polycondensation. Angew. Makromol. Chem. 1974, 39 (1), 7-20. 

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. 

The formation of a microcapsule wall through interfacial polycondensation/addition takes place in two steps. First step is the deposit of the oligomer (initial wall) at the oil droplet, and the second step is the wall thickness builds up. As described earlier, the polymerization occurs in oil phase, and the formed initial wall can limit the diffusion of the reactants. This reduces the polymerization rate that has great impact on the surface morphology and thickness of the microcapsule wall. - - Polycondensation by which polyamide, polyester, and polycarbonate microcapsules are prepared can generate acid byproduct during the process therefore, a base is needed to neutralize the acid and drive the reaction to complete. ... 

Interfacial polycondensation is an interesting procedure that is often used in demonstrations in polymer chemistry courses. Polyamides are prepared rapidly, in fiont of the class, from diacid chlorides and diamines. The products are removed quickly as they form, by pulling them out as a string from the interface." Polyesters can also be prepared from diacid chlorides and bisphenols. On the other hand, preparation of polyesters from glycols and diacid chlorides is usually unsuccessful due to low reactivity of the dialcohols. The diacid chlorides tend to undergo hydrolysis instead. Commercially, this procedure is so far confined mainly to preparations of polycarbonates (discussed further in this chapter). 

Polycarbonates are synthesized by interfacial polycondensation of bisphenol A and phosgene. The reaction is conducted in methylene chloride/water, and sodium hydroxide is used as a hydrogen chloride scavenger. Polycarbonates can also be synthesized by means of solution polymerization, using pyridine as the... 

Polycarbonates are manufactured either by transesterification or by interfacial polycondensation. In the transesterification method, bisphenol A is transesterified in two stages with a slight excess of diphenyl carbonate ... 

Polycarbonates are produced by interfacial polycondensation of the sodium salt of bisphenol A with phosgene. The aqueous phase from this process therefore always contains NaCI. 

Growing importance of BPA as the chemical intermediate is particularly connected with rapidly expanding fields of polycarbonates and epoxy resins. Presently, the main market for BPA is in production of the polycarbonates (66% of the BPA in global production capacity), and the primary commercial method for their synthesis is a homogeneous (usually in pyridine) or an interfacial polycondensation of BPA with phosgene as shown in Figure 7.13. 

In most cases (namely polyamides and polyureas), the polymer is insoluble in monomer BYB or in its solvent, and precipitates as soon as it forms, often yielding a shell through which AXA has to diffuse. Polycarbonates are an exception, as they are completely soluble in the methylene chloride solvent chosen for their production. Also, the organic phase is continuous in this latter case, which is a rather exceptional situation for interfacial polycondensations. 

Also with the exception of polycarbonates, interfacial polycondensation is mostly used in the production of specialty products, such as membranes [80-82] and microcapsules [83-87]. 

Furthermore, polycondensations of bisphenol-A and diphosgene were performed in a homogeneous phase with pyridine as catalyst and HCL acceptor. The excess of diphosgene was varied to compensate for the loss due to side reactions. After optimization of the reaction conditions the MALDl-TOF mass spectra displays again an almost exclusive formation of cyclic polycarbonates, but the highest Mn amounted only to 15 kDa. In other words, the interfacial polycondensations... 

Interfacially formed condensation polymers such as polyesters, polycarbonates, nylons, and PUs are typically formed on a microscopic level in a chain-growth manner largely because of the highly reactive nature of the reactants employed for such interfadal polycondensations. 

Pleated sheet conformation, 30,31 PLEDs (polymeric light-emitting diodes), 218 Plexiglas, 62 Plunkett, Roy, 65-66 PMMA. See Poly(methyl methacrylate) Polartec (Polar Fleece), 194 Poly(6-aminohexanoic acid), 25 Poly(a methyl styrene), 20 Polyacetylene, 72, 73 Polyacrylamide, 20 Polyamides, 22, 28, 61, 146 biodegradable, 185 Polyaramids, 77, 86 Polybutadiene, 70,109,148,155 Poly butyl acrylate), 20 Poly(butylene isophthalate), 25 Polycaprolactam, 21 Polycarbonate (PC), 17, 48, 86, 140 biodegradable, 185 density of, 247 impact strength of, 143 permeability of, 163 Polychloroprene, 65 Polycondensation, 85, 90-91 interfacial, 91-92... 

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... 

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