Polycarbonate resin, thermal degradation

Illustrative performance properties for a "general purpose polycarbonate," and for the same resin modified with the additive formulations "700" (without PTFE) and "800" (with PTFE) are summarized in Table IV (adapted from reference 32). It is clear that the objective of minimal effect on performance properties has been attained for this system. It is evident that flame retardant effectiveness attained with minimal levels of additive can provide optimum solutions to the problem of decreasing flammability without sacrifice in performance properties. Work documented to date suggests that in depth studies of thermal degradation such as reported for aromatic sulfonates in polycarbonates (28) would be rewarding for other systems. 

A comprehensive study of the thermal degradation of epoxy resins has been reported by Lee [239]. Their stability was found to be lower than that of polycarbonate, polyphenylene sulphide and teflon (Fig. 64). 

In both the Nylon 6,6 and polycarbonate tested, the resins typically degrade at the weakest link. For Nylon, the amide structure is the weakest link and thermal oxidative degradation of Nylon 6,6 occurs primarily by formation of a carbonyl with chain scission resulting in water loss. For polycarbonate, the... 

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. 

From TGA traces (see Figure 3.4) it can be readily seen that the cnred resins are much less thermally stable than Teflon or polycarbonate (PC). There is also an indication of a two-stage degradation for the cured DER 331 resin. From DTA traces for cured and uncured resins, it is shown that the characteristic exothermic peak between 300-380 °C is at least partially caused by some reaction of the epoxy group. 

FTIR techniques in combination with or as complement to other measurement techniques have been used in a wide range of photochemistry studies on polymers. These include bisphenol-A polycarbonate [173], polycarbonate coatings on mirrors [174], PMMA [175], poly( -butyl acrylate) [176] and polypropylene [177]. DSC and FTIR studies have been used in conjunction to investigate the nature of y-radiation-induced degradation and its effect on the 19°C and 30°C phase transitions in PTFE [178]. IR studies of the hydrolysis of melamine-formaldehyde crosslinked acrylic copolymer films have shown that copolymer-melamine formaldehyde crosslinks are broken and that crosslinks between melamine molecules are formed [179]. The thermal and photo-degradation mechanisms in an IR study of cured epoxy resins were found to be related to the autoxidative degradation processes for aliphatic hydrocarbons [180]. 

---