Acid sensitive polycarbonates

Ultramarine blues, reds and violets are acid sensitive. As such, their thermal and weathering properties are adversely affected in acidic media. Silica-encapsulated versions offer marked improvement in thermal stability and some improvement in weathering properties. The treated versions allow broad polymer usage, even in engineering plastics such as polycarbonate, and provide sufficient durability for automotive interior applications. Weatherability is highly dependent upon the degree of exposure to acid or alkaline conditions. 

Sodium antimonate must be used with halogen containing compounds for it to act as effective fire retardant. The source of chlorine may come from polymer (e.g., PVC, chlorinated rubber, etc.) or other chlorinated or brominated material. The benefits of using sodium antimonate over antimony oxide include its low tinting strength and the acid scavenging capability. For these reasons, it is used in semi-opaque or dark colored materials and in polymers such as polyesters and polycarbonates which are acid sensitive. 

Acid Catalyzed Hydrolysis. When photosensitive onium salts are incorporated into a film of a hydrolytically sensitive polycarbonate and exposed to ultraviolet irradiation, the acid which is produced catalyzes chain scission at random sites along the backbone (Equation 25). 

All of the eommereial alkyl eyanoaerylate monomers are low-viseosity liquids, and for some applications this can be an advantage. However, there are instances where a viseous liquid or a gel adhesive would be preferred, sueh as for application to a vertical surface or on porous substrates. A variety of viscosity control agents, depending upon the desired properties, have been added to increase the viscosity of instant adhesives [21]. The materials, which have been utilized, include polymethyl methacrylate, hydrophobic silica, hydrophobic alumina, treated quartz, polyethyl cyanoacrylate, cellulose esters, polycarbonates, and carbon black. For example, the addition of 5-10% of amorphous, non-crystalline, fumed silica to ethyl cyanoacrylate changes the monomer viscosity from a 2-cps liquid to a gelled material [22]. Because of the sensitivity of cyanoacrylate esters to basic materials, some additives require treatment with an acid to prevent premature gelation of the product. 

Polycarbonates and polysuipbones These are tough materials with heat resistance better than most thermoplastics. They are resistant to attack by acids and alcohols but the polycarbonates are sensitive to alkalis. 

Polystyrene-PDMS block copolymers4l2), and poly(n-butyl methacrylate-acrylic acid)-PDMS graft copolymers 308) have been used as pressure sensitive adhesives. Hot melt adhesives based on polycarbonate-PDMS segmented copolymers 413) showed very good adhesion to substrates with low surface energies without the need for surface preparation, such as etching. 

The acid and base sensitivity of condensation polymers whether or not under stress, e.g. polycarbonate, polyesters, polyamides and polysilanes under influence of acid or base the condensation bonds are hydrolysed under the cooperative action of mechanical stresses and the environment. A striking example is shown in Fig. 26.11, where the strength retention of PpPTA fibres is plotted versus pH after an exposure of 3 months at room temperature (Van den Heuvel and Klop). The hydrolysis of the polyamide is acid or alkali catalysed, in particular below pH = 3 and above pH = 9. 

Another example is thermally depolymerizable polycarbonates that are sensitized with onium salt cationic photoinitiators (139). As discussed previously (Section 3.2.3), one of the positive-negative resists based on polystyrene with pendant tertiary butyl carbonate protecting groups undergoes acid-catalyzed thermolysis to generate poly( p-vinylphenol), carbon dioxide, and isobutene. Therefore, if the tertiary butyl carbonate moiety is incorporated in the polymer backbone as a repeating unit, such polymers will... 

Polycarbonates are processed at very elevated temperatures (>300 °C) so that hydrolysis of the carbonate linkage to yield carbon dioxide and a phenol end group can occur if the polymer is not rigorously dried (residual water <0.02 wt.%). Complex chemistry can follow (Scheirs, 2000), resulting in the formation of low-molar-mass species and darkening of the polymer in addition to chain scission. The degradation is very sensitive to trace acidic or basic impurities, and it has been noted that in blends (e.g. PC/ABS) there may be initiation of the degradation by impurities in the ABS (Cook et al, 1996). 

In this discussion we deal with the resistance of polymers to various chemicals, (mainly water, acids, bases or organic solvents) as well as with their endurance after being exposed to climatic conditions or to fire. Most polymers show very low water absorbency, except for Nylon and cellulose derivatives that are sensitive to humidity. Most polymers also withstand mild inorganic chemicals at ambient temperatures. Excelling at this are the fluoro compoimds, Noryl, polyimide and polysulfone while polypropylene, PVC and epoxy are considered fair. Polyester and polycarbonate are sensitive to bases, while Nylon is affected by acids. Detailed tables of data exist, describing the resistance of plastics to many chemicals at specific temperatures. Most thermoplastics have a tendency to dissolve in specific organic solvents. 

Polyurethanes are sensitive to strong acids, strong alkalis, aromatics, alcohols, hot water, hot moist air and saturated steam. The hydrolytic stability of polyurethanes in applications must be considered carefully. However, polyurethanes are resistant to weak acids, weak alkalis, ozone, oxygen, mineral grease, oils and petroleum. There are doubts for the oxidation stability of polytetramethylene ether glycol based polyurethanes. Polycarbonate urethane is a promising substitute with good oxidation stability. 

Polymers resistant to hydrolysis in all media include polyolefins, hydrocarbon rubbers, polystyrene, polytetrafluoroethylene, and implasticized poly(vinyl chloride). Polymers sensitive to hydrolysis in both alkaline and acidic media are, eg, cellulose esters, plasticized poly(vinyl chloride), polyCmethyl methacrylate), polyacrylonitrile, polyoxymethylene, polyamides, polyesters, polycarbonates, and polysulfones. Polymers sensitive to alkalis but not acids are imsaturated polyester resins and phenol-formaldehyde resins. 

These polymers are sensitive to thermolysis and decomposes rapidly and smoothly to bisphenol A, carbon dioxide, and volatile dienes when heated near 200 . For example polymer 8 affords only benzene, carbon dioxide, and bisphenol A upon heating. As in the case with t-butyl esters and carbonates, this thermolysis reaction is susceptible to acid catalysis and this property forms the basis of our resist design. The tertiary polycarbonate resist is formulated by casting a polymer film from a solution containing a few percent of substances which will produce strong acid upon photolysis. 

Freitag and Reinking reported on the property profile of Bayer s commercial polyarylate [31], They observed that polyarylate was less sensitive to specimen thickness than polycarbonate in the notched izod impact test. They stated that polyarylate is quite similar to polycarbonate in hydrolytic degradation by alkalis, dilute acids, and hot water. The injection moldability... 

Amorphous polyamides, preferably copolyamides from iso- and terephthalic acid with hexamethylene diamine have gained importance as components in polymer blends with polycarbonate, polyphenylene ether and/or functionalized elastomers, and also with the semi-crystalline polyamides 6 and 66. These copolyamides increase the chemical resistance of polycarbonate or polyphenylene ether and reduce stress-cracking sensitivity to concentrated zinc chloride solution in polyamide 6 and 66. Moreover, these copolyamides provide for improved compatibility. 

Table 1.20 shows the influence of acid rain on various materials. Under strictly artificial weathering conditions, only polycarbonate and unstabilized polyamide 6 clearly exhibit graying. The other specimens show no visible changes. Acid rain (in the ADF test) leads to obvious changes in all materials. There are recognizable differences in the order resulting from acid concentration, especially between ABS and PBT specimens. ABS appears to react particularly sensitively to acid concentration, whereas PBT reacts to extended UV radiation. 

---