Polycarbonates preparation

A reexamination of polycarbonate chemistry was carried out about 50 years after the first aromatic polycarbonates of resorcinol and hydroquinone were discovered. In independent investigations at Bayer AG and General Electric, it was discovered that the polycarbonates of BPA could be prepared (eq. 2). Unlike the ahphatic polycarbonates prepared earlier, which were either hquids or low melting sohds, the aromatic polycarbonates were amorphous sohds having elevated glass-transition temperatures. 

Lexan, a polycarbonate prepared from diphenyl carbonate and bisphenol A, is another commercially valuable polyester. Lexan has an unusually high impact strength, making it valuable for use in telephones, bicycle safety helmets, and laptop computer cases. 

Zhou M, Takayanagi M, Yoshida Y, Ishii S, Noguchi H (1999) Enzyme-catalyzed degradation of aliphatic polycarbonates prepared from epoxides and carbon dioxide. Polym Bull 42(4) 419 24... 

TABLE 1. Physical Properties of Polycarbonate Prepared Using Bisphenol A, 3,3-bis(4-hydroxy-phenyl)-l-phenyl-lH-indol-2-one, and Phosgene Dissolved in C Cb/Chlorobenzene at Ambient Temperature... 

TABLE 1. Polycarbonates prepared by reacting diphenyl carbonate with isosorbide and bisphenol A. 

Polycarbonates prepared by reacting phosgene and bisphenol A and capping with a perfluoroalcohol, (III), were prepared by Davis [3] and used as the surface layer of molded articles in flame retardant and weatherable articles. 

When the polycarbonate of bisphenol A was made interfacially in a non-solvent for the polymer the distribution of molecular weights showed two clear maxima and was unusually broad [40]. This was probably a consequence of the two-step process often employed in the preparation of polycarbonates here, the first step yields low-molecular-weight polymer from phosgene and the aqueous alkaline solution of the aromatic diol, then an accelerator salt and more alkali and phosgene are added in the second step. Polycarbonates prepared in the melt and in solution show the expected essentially statistical distribution of molecular weights [40]. Polycarbonates have also been prepared from bisphenols and bisphenol bischloroformates studies of this reaction in nitrobenzene solution have shown it to be second order [79]. 

Sobiczewski, Z. Wielgosz, Z. Stability of polycarbonates prepared from chlorinated bisphenols. Plaste Kautschuk 1968, 15, 176-179. 

TCBF copolycarbonates (1/8 inch thickness) showed stress cracking resistance to ceurbon tetrachloride under moderate stress the mixed TCBF copolycarbonate did not crack even under strong stress. Molded pieces of all the other polycarbonates prepared cracked immediately upon exposure to ceurbon tetrachloride. Acetone and xylene were found to indiscriminately attack both stressed films euid molded pieces of all the polycarbonates tested. 

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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