Polycarbonate resins

Phosgene (for toluene diisocyanate, dipbenylmetbane diisocyanate, and polycarbonate resin manufacture), cbloroisocyanuric acid, cyanuric cbloride. 

Chemical Manufacturing. Chemical manufacturing accounts for over 50% of all U.S. caustic soda demand. It is used primarily for pH control, neutralization, off-gas scmbbing, and as a catalyst. About 50% of the total demand in this category, or approximately 25% of overall U.S. consumption, is used in the manufacture of organic intermediates, polymers, and end products. The majority of caustic soda required here is for the production of propylene oxide, polycarbonate resin, epoxies, synthetic fibers, and surface-active agents (6). 

In general, polycarbonate resins have fair chemical resistance to aqueous solutions of acids or bases, as well as to fats and oils. Chemical attack by amines or ammonium hydroxide occurs, however, and aUphatic and aromatic hydrocarbons promote crazing of stressed molded samples. Eor these reasons, care must be exercised in the choice of solvents for painting and coating operations. Eor sheet appHcations, polycarbonate is commonly coated with a sihcone—sihcate hardcoat which provides abrasion resistance as well as increased solvent resistance. Coated films are also available. 

Fig. 2. Stress—strain curve for standard polycarbonate resin at 23°C where the points A, B, and C correspond to the proportional limit (27.6 MPa), the yield point (62 MPa), and the ultimate strength (65.5 MPa), respectively. To convert MPa to psi, multiply by 145.

ABS can be blended with bisphenol A polycarbonate resins to make a material having excellent low temperature toughness. The most important apphcation of this blend is for automotive body panels. 

Bisphenol A Polycarbonate Resins. These resins are manufactured by interfacial polymerization (84,85). A small amount of resin is produced by melt-polymerization of bisphenol with diphenyl carbonate in Russia and the People s RepubHc of China. Melt technology continues to be developmental in Japan and the West, but no commercial activities have started-up to date, although some were active in the late 1960s. No reports of solvent-based PC manufacture have been received. 

Unless great care is taken in control of phenol/acetone ratios, reaction conditions and the use of catalysts, a number of undesirable by-products may be obtained such as the o-,p- and o-,o- isomers of bis-phenol A and certain chroman-type structures. Although tolerable when the bis-phenol A is used in epoxy resins, these have adverse effects on both physical properties and the colour of polycarbonate resins. 

Residual traces of these impurities must thus be removed by some technique such as recrystallisation from chlorobenzene or acqueous alcohol. The melting point is a useful measure of purity and for polycarbonate resins the melting point should be in the range 154-157°C compared with values of 140-150°C for epoxy resin grade bis-phenol A. 

Polymerisation then proceeds by splitting out of diphenyl carbonate to give the polycarbonate resin (Figure 20.4 (b)). 

Unless the hydroxyl groups have such proximity that cyclisation takes place, polycarbonates will normally be produced whenever phosgene or a carbonate ester is reacted with a polyhydroxy compound. This means that a very large range of polycarbonate resins are possible and in fact many hundreds have been prepared. 

Christopher and Fox have given examples of the way in which polycarbonate resins may be tailor-made to suit specific requirements. Whereas the bis-phenol from o-cresol and acetone (bis-phenol C) yields a polymer of high hydrolytic stability and low transition temperature, the polymer from phenol and cyclohexanone has average hydrolytic stability but a high heat distortion temperature. By using a condensate of o-cresol and cyclohexanone a polymer may be obtained with both hydrolytic stability and a high heat distortion temperature. 

A variety of synthetic polymers, including polycarbonate resins, substituted olefins, and polyelectrolyte complexes, are employed as ultrafiltration membranes. Many of these membranes can be handled dry, have superior organic solvent resistance, and are less sensitive to temperature and pH than cellulose acetate, which is widely used in RO systems. 

They are also important chemical intermediates. For example, acetone is used to make methyl methacrylate (the starting material for Plexiglas and Lucite plastics), methyl isobutyl ketone, and Bisphenol A (used in epoxy and polycarbonate resins). 

Diphenylcarbonate (DPC) is a key monomer for producing LEXAN polycarbonate resin by melt polymerization reaction of DPC with Bisphenol A. Currently, DPC is produced by General Electric Company (GE) in Cartagena, Spain, using a two-step process (Eq. 1) The stoichiometric carbonylation of... 

Polycarbonates are manufactured via interfacial polymerization or through a melt esterification process. The properties of polycarbonate can differ greatly based on the method of polymerization. Specifically, the molecular weight distributions created by the two methods differ because of kinetic effects. Polycarbonates manufactured via interfacial polymerization tend to be less stable at high temperatures and less stiff than those produced via melt esterification, unless proper manufacturing precautions are taken. Therefore, when choosing a polycarbonate resin grade for a specific application, it is important to know the method by which it was produced. Either polymerization method can be performed as a continuous or batch process. 

Why are polycarbonate resins easy to process via injection molding ... 

Blends of flame retardant additives have been advocated as an approach to an optimum balance of properties in the finished products. For example, blends of tetrabromophthalate esters with de-cabromodiphenyl oxide or other flame retardants are reported to yield a V-0 rating in modified PPO and in polycarbonate resins without compromising melt processability or performance properties (23a-b). 

An example of a direct comparison of performance properties with and without added flame retardants for "New ignition resistant polycarbonate resins" is provided in a paper by workers at the Dow Chemical Company (32). The technology of the flame retardant additives is de scribed as including... 

The brominated phosphate is an efficient flame retardant for polycarbonate resin. UL-94 ratings of V-0 with oxygen index values of greater than 40 are obtained. Polycarbonate resin containing brominated phosphate processes with greater ease than resin containing brominated polycarbonate as measured by injection molding spiral flow measurements. The heat distortion temperature is reduced... 

Flame retardant sulfonate salt polycarbonate resin gives a UL-94 rating of V-0 at 1/16 inch thickness. At 1/32 inch thickness, however, the product drips to give a V-2 rating. The addition of 3% brominated phosphate renders the product V-0 at 1/32 inch thick (Table III). 

A 50/50 blend of polycarbonate resin and PBT polyester containing 13.5% brominated phosphate and no antimony oxide results in a product with a V-0 rating and an oxygen index of 33. An equivalent product containing brominated polycarbonate has a low oxygen index and burns in the UL-94 test (Table VIII). 

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