Radiation polysulfones

Radiation Resistance. Polysulfones exhibit resistance to many electromagnetic frequencies of practical significance, including microwave, visible, and infrared. Especially notable is the excellent resistance to microwave radiation, which has contributed to the excellent fit of polysulfones in cookware appHcations. Polysulfone also shows good resistance to x-rays, electron beam (24), and gamma (25,26) radiation under many practical appHcation conditions. 

Polysulfones also offer desirable properties for cookware appHcations, eg, microwave transparency and environmental resistance to most common detergents. Resistance to various sterilizing media (eg, steam, disinfectants, and gamma radiation) makes polysulfones the resin family of choice for many medical devices. Uses in the electrical and electronic industry include printed circuit boards, circuit breaker components, connectors, sockets, and business machine parts, to mention a few. The good clarity of PSF makes it attractive for food service and food processing uses. Examples of appHcations in this area include coffee decanters and automated dairy processing components. 

Sulfur dioxide was the major volatile product and was used as a probe to correlate the radiation resistance with polymer structure. The use of biphenol in the polymer reduced G(SO ) by 60% compared with bisphenol A based systems (Bis-A PSF). Surprisingly, the isopro-pylidene group was shown to be remarkably radiation resistant. The ultimate tensile strain decreased with dose for all polysulfones investigated and the rate of decrease correlated well with the order of radiation resistance determined from volatile product measurements. The fracture toughness (K ) of Bis-A PSF also decreased with irradiation dose, but the biphenol based system maintained its original ductility. 

Figure 12. Variation of the yield of radicals determined by ESR with radiation dose for bisphenol-A aromatic polysulfone showing (D) dose saturation and ( ) effect of photobleaching.

The presence of aromatic groups in polymers greatly reduces their radiation sensitivity. Aromatic polysulfones are commercially important engineering plastics with high temperature resistance and also show good radiation resistance (16). Development of polymers with improved radiation resistance should be possible by copolymerization of other aromatic structures into the chain. 

The GPC technique was used to determine gel formation. Figure 13 shows the soluble fraction of aromatic polysulfone I measured with this technique after irradiation at 30 and 150°C. The relative radiation resistance of different polymers can be obtained by comparison of the gel doses (the highest dose for complete solubility of the polymer) provided that the initial molar masses of the of the polymers are known, or from G(S) and G (X) values these can be derived from the dose dependence of the soluble fractions beyond the gel dose, using a Charlesby-Pinner, or Saito-type plot with allowance for the molar mass distribution. 

In recent years, remarkable progress has been made in the syntheses of aromatic and heterocyclic polymers to search a new type of radiation resistant polymers. Sasuga and his coworkers extensively investigated the radiation deterioration of various aromatic polymers at ambient temperature [55-57] and reported the order of radiation resistivity evaluated from the changes in tensile properties as follows polyimide > polyether ether ketone > polyamide > polyetherimide > polyarylate > polysulfone. 

The preliminary electron beam experiments on all aromatic polyfarylene ether sulfone)s were performed by Hedrick et al. [58] and the detailed investigation on radiation effects of these polymers were recently carried out by Lewis et al. [59]. They found that an aromatic polysulfone based on 4,4 -biphenol and 4,4 -dichlorodiphenyl sulfone exhibited the highest radiation tolerant in a systematic series of polyfarylene ether sulfone)s with "/-irradiation up to 4 x 106 Gy. 

Poly(butene-l sulfone) (PBS), a sensitive, positive, electron beam resist, is highly sensitive to 185-nm radiation (Table 3.4) (9). However, PBS does not absorb above 200 nm, and the sensitization has not been successful. Incorporation of pendant aromatic rings into the polysulfone structure extends the photosensitivity to the DUV and mid-UV regions (72). Himics and Ross (73) reported that carbonyl-containing poly(olefin sulfones) such as poly(5-hexen-2-one sulfone) are sensitive to UV-induced degradation and... 

Membrane filtration application to biopharmaceutical product development is extremely important since sterile protein-peptide products can only be prepared via sterile filtration and gamma radiation steam cannot be used under pressure. There are several excellent works in the field of sterile membrane filtration.34-36 The filter media most often tested for protein formulations with minimum adsorption and maximum compatibility are mixed esters of cellulose acetate, cellulose nitrate, polysulfone, and nylon 66. Membrane filters must be tested for compatibility with the active drug substance and selected for formulations if they have the lowest adsorption and maximum compatibility with the product. 

Improvement of surface hardness of some polymers by radiation processing at high temperatures — Gamma-ray or electron beam irradiation at high temperature and at a small dose improved the Rockwell hardness and resistance to wear for polycarbonate and polysulfone. The effective temperature during irradiation was the glass transition temperature of respective polymer, and the dose at maximum hardness was only 3-5 kGy [3], The improvement in hardness and wear resistance was supposed to be dense... 

Polysulfones have found use as resists in the area of mierolithography since the polysulfones are unstable toward radiation and heat below their melting points and the SO2 and olefin degradation products are volatile. It is interesting to note that some olefins undergo isomerization during the radiation induced degradation step [9c]. 

PSF is resistant to repeated sterilization by several techniques including steam autoclave, dry heat, ethylene oxide, certain chemicals, and radiation. It will stand exposure to soap, detergent solutions, and hydrocarbon oils even at elevated temperatures and imder moderate stress levels. Polysulfone is unaffected by hydrolysis and has a very high resistance to mineral acids, alkali, and salt solutions. PSF is not resistant to polar organic solvents such as ketones, chlorinated hydrocarbons, and aromatic hydrocarbons. 

Polysulfone has good weatherability, and it is not degraded by UV radiation. Refer to Table 2.34 for the compatibility of PSF with selected corrodents. Reference [1] provides a more comprehensive listing. 

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