Polystyrene degradation resistance

Figure 5.126 summarizes the relative radiation resistance of plastics. At higher doses, all plastics are increasingly damaged, whereby the most resistant plastics (epoxy resins, polystyrene, polyimide) resist doses as high as 10 MGy. Excessive crosslinking and degradation result in embrittlement. 

Compared with tar, which has a relatively short lifetime in the marine environment, the residence times of plastic, glass and non-corrodible metallic debris are indefinite. Most plastic articles are fabricated from polyethylene, polystyrene or polyvinyl chloride. With molecular weights ranging to over 500,000, the only chemical reactivity of these polymers is derived from any residual unsaturation and, therefore, they are essentially inert chemically and photochemically. Further, since indigenous microflora lack the enzyme systems necessary to degrade most of these polymers, articles manufactured from them are highly resistant or virtually immune to biodegradation. That is, the properties that render plastics so durable... 

The resistance to gamma radiation is excellent without significant degradation after more than 1000 Mrad, exceeding even the behaviour of polystyrene. With alpha and beta radiations, resistance would be higher than 10 000 Mrad. 

As an alternative, stable high-coverage nonpolar RPC sorbents phases have been prepared by cross-linking hydrophobic polymers at the silica surface, either via free radical 143 or condensation 101 polymerization chemistry. In this case, the underlying silica becomes partly protected from hydrolytic degradation due to the presence of the hydrophobic polymer film coating that effectively shields the support material. Similar procedures have been employed to chemically modify the surface of other support materials, such as porous zirconia, titania, or alumina, to further impart resistance to degradation when alkaline mobile-phase conditions are employed. Porous polystyrene-divinylbenzene sorbents, be-... 

As block copolymers are still rather expensive materials, it may be advantageous to use them as additives to important industrial polymers. In this domain, possibilities are extremely numerous and diverse. They include an improvement of chemical properties such as resistence to degradation agents, or rheological properties such as adhesion of vinylic paints, high impact properties of conventional thermoplastics, or a compatibilization of polyolefins, polystyrene and poly(vinyl chloride) allowing the reuse of polymeric waste products. The above examples illustrate the great intrinsic potential of block copolymers in the quest of new materials with specific properties. 

Initial processing experiments showed however, that under typical O2 RIE conditions (power 0.1 to 0.2 W/cm self-bias — —250 to —350 V, pressure — 5 to 20 mTorr O2), these resists are not very resistant, particularly under prolonged etching. Effective pattern transfer may require etch times of 15 to 30 min (11,12). which are sufficient to cause extensive degradation of the resist. Such behavior is reminiscent of poly (olefin sulfone)s such as the well-known PBS e-beam resist, which is etched 5-7 times faster than polystyrene in an oxygen plasma (5). 

The majority of reversed-phase methods have been developed on covalently modified silica gel and the most popular stationary phase is octade-cylsilyl silica (ODS, Cig). Polymeric supports, such as functionalized polystyrene-divinylbenzene copolymers (MacBlane et al., 1987), are particularly useful when mobile phases of higher pH are required because of their resistance to degradation in alkaline solutions. The main drawback of polymeric supports is their reduced column efficiencies and their lower mechanical resistance to high pressures compared with silica gel. 

Compared with acrylic glass, polystyrene has a lower light stability and resistance to ultraviolet radiation. The slight degradation when exposed to ultraviolet radiation is a disadvantage that occurs with all optical plastics. The higher refractive index of polystyrene permits its use in conjunction with acrylic lenses for the design of colour-... 

Styrenic plastics such as acrylonitrile/butadiene/styrene graft copolymers (ABS) and impact-resistant polystyrenes are very sensitive towards oxidation, mainly because of their butadiene content. Degradation on weathering starts at the surface and results in rapid loss of mechanical properties... 

---