Diphenyl polycarbonate production

However, for AA and BB systems, like those shown in Table 7.1, stoichiometric imbalance can occur, with serious consequences for the polymerization. The molar ratio of the two types of functional end-groups (A and B) that are available for polymerization is determined by the initial molar ratio of the two monomers in a batch reactor, and by any monomers or oligomers that might escape from the reacting mixture during the polymerization. Note that escape of volatile monomers with the resulting influence on the ratio of functional groups is a serious practical problem for some industrial polymerizations that use volatile monomers (e.g., HMD in nylon 6,6 production and diphenyl carbonate in polycarbonate production). 

The solventless reaction in the presence of diallq ltin(iv) complexes led to a conversion of 42% with 78% selectivity to diphenyl carbonate. Starting from phenyl acetate, total conversion was obtained at 220 "C with higher selectivity to diphenyl carbonate (95%). Transesterification with higher alcohols was also examined, giving better conversion due to higher nucleophilicity compared to phenol. However, a steric effect was evidenced as fert-butanol was unreactive. Transesterification of ethylene carbonate (l,3-dioxolan-2-one) with methanol to dimethyl carbonate was also reported early. " Today, both transesterifications with methanol and phenol are integrated into the value chain of bisphenol-A polycarbonate production and commercialised by Asahi Kasei Corporation (Scheme 21.12). ... 

Bromine compounds are often used as flame retardant additives but 15-20ptsphr may be required. This is not only expensive but such large levels lead to a serious loss of toughness. Of the bromine compounds, octabromo-diphenyl ether has been particularly widely used. However, recent concern about the possibility of toxic decomposition products and the difficulty of finding alternative flame retarders for ABS has led to the loss of ABS in some markets where fire retardance is important. Some of this market has been taken up by ABS/PVC and ASA/PVC blends and some by systems based on ABS or ASA (see Section 16.9) with polycarbonates. Better levels of toughness may be achieved by the use of ABS/PVC blends but the presence of the PVC lowers the processing stability. 

Crystallisable polymers have also been prepared from diphenylol compounds containing sulphur or oxygen atoms or both between the aromatic rings. Of these the polycarbonates from di-(4-hydroxyphenyl)ether and from di-(4-hydroxy-phenyl)sulphide crystallise sufficiently to form opaque products. Both materials are insoluble in the usual solvents. The diphenyl sulphide polymer also has excellent resistance to hydrolysing agents and very low water absorption. Schnell" quotes a water absorption of only 0.09% for a sample at 90% relative humidity and 250°C. Both the sulphide and ether polymers have melting ranges of about 220-240°C. The di-(4-hydroxyphenyl)sulphoxide and the di-(4-hydroxy-phenyl)sulphone yield hydrolysable polymers but whereas the polymer from the former is soluble in common solvents the latter is insoluble. 

The oxidative carbonylation of alcohols and phenols to carbonates can be catalyzed by palladium or copper species [154-213]. This reaction is of particular practical importance, since it can be developed into an industrial process for the phosgene-free synthesis of dimethyl carbonate (DMC) and diphenyl carbonate (DPC), which are important industrial intermediates for the production of polycarbonates. Moreover, DMC can be used as an eco-friendly methylation and carbonylation agent [214,215]. The industrial production of DMC by oxidative carbonylation of methanol has been achieved by Enichem [216] and Ube [217]. 

The tetrazole (66) decomposes to yield nitrogen and a residue consisting of three main components aminodiphenyltriazole, 3,5-diphenyl-l,2,4-triazole and triphenyl-s-triazine (81MIH510, 69USP3442829). The inert nature of the decomposition products makes (66) suitable for use with high temperature polymers such as polycarbonate, polyester and Nylon 6. 

Diphenyl carbonate is an important intermediate in the production of bisphenol-A-polycarbonate (BPA-PC). The technology shift from phosgene to DPC to produce BPA-PC on a commercial scale also allows the number of applications of this type of polymer to be increased for example, high-performance BPA-PCs utilized for information storage (e.g., DVDs) are prepared from high-purity DPC. The chemical route to this DPC brand is based on a two-step reaction, namely transesterification followed by disproportionation (Equations 7.4 and 7.5). 

Komiya et al. [13] recently introduced the novel, environmentally friendly process from Asahi Chemical Industry Co. for the production of polycarbonates, which requires neither phosgene nor solvent (Scheme 1). In this process bisphenol A undergoes a prepolymerization with diphenyl carbonate in the melt. A simple crystallization of the prepolymer is fol-... 

Mixed esters, such as isopropylphenyl diphenyl phosphate and tcrt-butylphenyl diphenyl phosphate, are also widely used as both plasticizers/flame retardants for engineering thermoplastics and hydraulic fluids.11 These esters generally show slightly less flame-retardant efficacy, when compared to triaryl counterparts however, they have the added advantage of lower smoke production when burned. Some novel oligomeric phosphate flame retardants (based on tetraphenyl resorcinol diphosphate) are also employed to flame retard polyphenylene oxide blends, thermoplastic polyesters, polyamides, vinyls, and polycarbonates. 

Diphenyl carbonate can be made from dimethyl carbonate by exchange with phenol (2.9).32 It can also be made directly from phenol (2.10), but the yields are not as high.33 A combination of palladium and manganese catalysts is used. The water formed is sparged out with excess reaction gas to shift the reaction to the desired product. Diphenyl carbonate is preferred over dimethyl carbonate for production of polycarbonates. 

Fig. 71. Amount of volatile products evolved from polycarbonate at 360°C with respect to time A, C02 B, bisphenol A C, phenol D, 2-( para-hydroxy phenyl )-2-phenylpropane E, CO F, CH4 G, diphenyl carbonate [298].

Polycarbonates of numerous bisphenols have been extensively studied. However, most commercial polycarbonates are derived from bisphenol A. At first, both direct-reaction and melt-transesterification processes were employed (Figure 4). In direct-reaction processes, phosgene reacts directly with bisphenol A to produce a polymer in a solution. In transesterification, phosgene is first reacted with phenol to produce diphenyl carbonate, which in turn reacts with bisphenol A to regenerate phenol for recycle and molten, solvent-free polymer. Transesterification is reported to be the least expensive route. It was phased out, however, because of its unsuitability to produce a wide range of products. 

Application The Polimeri/Lummus process is a phosgene-free route for the production of diphenyl carbonate (DPC)—a polycarbonate intermediate—from dimethyl carbonate (DMC) and phenol. The Polimeri/Lummus DPC process has no environmental or corrosion problems, and the byproduct methanol can be recycled back to the DMC process. 

Transesterification of diphenyl carbonate and bisphenol A. The final step in the nonphosgenation process for polycarbonates is the reaction of bisphenol A (BPA) and the carbonate ester, diphenyl carbonate (DPC). Research has focused on the transesterification melt process because it has the advantage over the conventional interfacial process of allowing the reaction of the diphenyl carbonate and bisphenol A to take place completely in the liquid phase. The disadvantage of this approach is that elevated temperatures are needed to ensure that unreacted DPC and BPA are completely volatilized from the product. Only a lower molecular weight (30,000-50,000) polymer can be made in this way. Typical molecular weights for polycarbonate produced by phosgenation in the interfacial pro-... 

In the examples provided in this section, combinatorial methods were used to improve the properties of an industrial aromatic polymer, such as melt-polymerized bisphenol-A polycarbonate. The reactions were performed in 96-well microtiter glass plates that served as 96-microreactor arrays in a sequence of steps of increasing temperature with a maximum temperature of 280°C. An example of one of the 96-microreactor arrays after melt-polymerization is shown in Figure 5.3A. For melt-polymerization of bisphenol-A polycarbonate, the starting reaction components included diphenyl carbonate and bisphenol-A monomers and a catalyst (e.g., NaOH). The materials codes used in the examples are presented in Table 5.2. Intermediate species include polycarbonate oligomers and phenol. The bisphenol-A polycarbonate polymer often contains a branched side product that produces a detectable fluorescence signal and other species that can include nonbranched end-groups and cyclics. We used fluorescence spectroscopy for nondestructive chemical analysis of melt-polymerized bisphenol-A polycarbonate. The key attractive... 

Asahi Chemical Industry Co., Ltd. has succeeded in developing alternative and innovative non-phosgene processes for producing isocyanates and polycaihonates in the pilot scales which are commercially viable. In the production of isocyanates, processes for both aromatic isocyanates, such as methylene diphenyl diisocyanate (MDI), and aliphatic isocyanates, such as hexamethylene diisocyanate (HDI) or isophoione diisocyanate (IPDI), have already been developed successfully. A part of those processes has already been reported (i), and the others will be reported in the near future. In this paper, the new iimovative process for producing polycarbonates is reported. 

The polymer is exposed to an extensive heat history in the melt process. Early work on transesterification technology was troubled by thermal-oxidative reactions of the polymer, especially in the presence of basic catalysts (8-11). Early polycarbonates prepared by Fox and others via the melt process had noticeable brown colors. More recent work on catalyst systems, more reactive carbonates, and modified processes have improved the process to the point where formation of color and product decomposition can be effectively suppressed. Polymers with color at least as good as interfacially prepared materials can now be prepared commercially. One of the key requirements for the transesterification process is the use of clean starting materials. Methods for the purification of both BPA and diphenyl carbonate have been developed and patented. Activated carbonates that form high molecular weight polycarbonate at equilibrium in solution at or below room temperature have also been reported, although they are chiefly only of academic interest (66,67). 

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