Polycarbonate stabilization methods

A cumulative success of artificial ion-channel functions by simple molecules may disclose a wide gate for the design of ion channels and possible applications to ionics devices. Incorporation of these channels into bilayer lipid membrane systems may trigger the developments towards ionics devices. The conventional BLM system, however, is not very stable, one major drawback for the practical applications, and some stabilization methods, such as impregnating the material in micro-porous polycarbonate or polyester filters, are required. On the other hand,... 

Peng S, Dong L, Zhuang Y, Chen C (2001) Method for improving thermal stability of aliphatic polycarbonate using organic silanes, CN 1306022. CAN 137 34001... 

Methods for isolation of the product polycarbonate remain trade secrets. Feasible methods for polymer isolation include antisolvent precipitation, removal of solvent in boiling water, spray drying, and melt devolatization using a wiped film evaporator. Regardless of the technique, the polymer must be isolated dry, to avoid hydrolysis, and essentially be devoid of methylene chloride. Most polycarbonate is extmded, at which point stabilizers and colors may be added, and sold as pellets. 

This process—injection compression moulding—offers other advantages besides lower clamping forces compression of the hot melt gives excellent surface finish and lower pressure at injection reduces orientation in the melt, so improving dimensional stability. The method is used currently to make compact discs of high quality from polycarbonate. 

CEs are known to react with phenols to form iminocarbonates which eventually lead to polycyanurates with the liberation of more acidic phenol moiety. This can be a method to alter the gel point of the resin, Tg, and thermal stability of the network by co-curing diphenol with CE. Thus, copolymerization of dicyanate with diphenols resulted in polycyanurates with altered network structure and diminished crosslink density [237]. However, an earlier report claims poly(imi-nocarbonate) by reaction of these two in equimolar quantities. The thermoplastic so formed was reported to retain the mechanical properties like a polycarbonate. This approach can produce strong, non-toxic, biodegradable films and molded plastics that are degradable at temperatures above 140 °C [169,238]. Except for a few very early reports [239], the reaction of CE with anhydrides to form poly(iminocarbamates) has not been explored much. 

In the oxidation of polyvinyl chloride, for example, a vital role is played by splitting out of HCl molecules and the formation of double bonds. The oxidation of polyamides proceeds without any appreciable induction period and differs sharply in character from the oxidation of hydrocarbons. The thermooxidative destruction of polysiloxanes also proceeds uniquely. Condensation polymers - epoxide resins, polyary-lates, and polycarbonates begin to be oxidized at comparatively high temperatures, and thus far no methods of stabilizing them are known. 

Lundy, C., et al. Methods of Color Stabilization in Gamma-Radiation-Sterilized Polycarbonate. SPE-ANTEC, Apr. 1988. 

Processes were developed in recent years in order to recover raw materials from poly(ethylene terephtalate) (PET) and polycarbonate (PC) by hydrolysis. The main focus was the recovery of terephthalic acid and ethylene glycol besides other products such as benzene, salts of terephthalic acid and oxalic acid. Processes developed for PET are also valid for polyesters such as poly(butylene terephthalate) (PBT) and poly(ethylene 2,6-napthalene dicarboxylate) (PEN). The recovery of bisphenol-A (BPA) from PC requires more sophisticated methods due to the low stability of BPA at high temperatures. Often phenol and isopropenyl phenol are obtained as degradation products of BPA. 

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