Polycarbonates—continued

Electrical, electronic, and technical appHcations use polycarbonates for a variety of purposes. The woddwide market is about 156,000 t aimuaHy. Because of exceHent electrical properties (dielectric strength, volume resistivity), and resistance to heat and humidity, polycarbonate is used for electrical connectors (qv), telephone network devices, oudet boxes, etc. Polycarbonate had been popular for use in computer and business machine housings, but the use of neat resin has been largely supplanted by blends of polycarbonate with ABS. OveraH, however, the total use of polycarbonate continues to increase. 

Polypropylene sheet has been used most extensively however, thermoplastic polyester, polycarbonate, and nylon versions are available (see Elastomers, synthetic Polycarbonates). Continuous strand glass fiber mat is the typical reinforcement. The limited number of sheet suppHers reduces potential for competitive pricing. 

Polycarbonates (continued) Poly [2,2-pentane bis(4-phenyl)carbonate] 282.3 >1.13 ... 

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. 

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. 

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. 

The most desirable property of polycarbonates is their high ductility on impact, relative to other engineering polymers in the unmodified state. There is no consensus on the mechanism of ductility researchers continue to explore this behavior through molecular dynamics studies of chain segment motion during the formation of crazes and propagation of the failure. 

We previously reported that brominated aromatic phosphate esters are highly effective flame retardants for polymers containing oxygen such as polycarbonates and polyesters (9). Data were reported for use of this phosphate ester in polycarbonates, polyesters and blends. In some polymer systems, antimony oxide or sodium antimonate could be deleted. This paper is a continuation of that work and expands into polycarbonate alloys with polybutylene terephthalate (PBT), polyethylene terephthalate (PET) and acrylonitrile-butadiene-styrene (ABS). 

Figure 3. NBS Smoke Chamber results (non-flaming) for two grades of polycarbonate structural foam. Continued on next page.

The continuous use temperatures in an unstressed state are generally estimated from 90°C up to 125°C for general-purpose grades and up to 140°C for heat-resistant polycarbonates if the softening or melting temperatures are higher. 

Injection molding is employed to stamp out copies of the master discs from polycarbonate. The molded polycarbonate discs are cooled and hardened quickly, within about 4—6 sec, and evenly. The dye layer is then applied. The applied dyes are often proprietary and continually modified in an attempt to get a better dye. The dye must be compatible with the system and adhere to the polycarbonate base. It is applied by spin coating i.e., the disc is spun and the dye is sprayed onto the surface. The dye is then dried and cured. 

World War II helped shape the future of polymers. Wartime demands and shortages encouraged scientists to seek substitutes and materials that even excelled those currently available. Polycarbonate (Kevlar), which could stop a speeding bullet, was developed, as was polytetrafluoroethylene (Teflon), which was super slick. New materials were developed spurred on by the needs of the military, electronics industry, food industry, etc. The creation of new materials continues at an accelerated pace brought on by the need for materials with specific properties and the growing ability to tailor-make giant molecules macromolecules—polymers. 

Figure 18 Stability test carried out with two sealed DSSCs over 7000 hr of continuous illumination with visible light (polycarbonate 395-nm cutoff filter) at 1000 W/m2 light intensity. The photocurrent and voltage drop measured across an external load resistor of 10 ft are plotted as a function of irradiation time. Cell 1 (solid line) was continuously illuminated at 35°C the same for cell 2 (broken line) except that it was operated for a 700-hr period at 75°C and for 1000 hr at an open circuit. (From Ref. 153.)...

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