Poly ionizing radiation

Polyimide. Polyimide is a biaxiaHy oriented high performance film that is tough, flexible, and temperature- and combustion-resistant. Its room temperature properties compare to poly(ethylene terephthalate), but it retains these good characteristics at temperatures above 400°C. Its electrical resistance is good and it is dimensionally stable. The principal detriment is fairly high moisture absorbance. The main uses are for electrical insulation, particularly where high temperatures are prevalent or ionizing radiation is a problem. The films may be coated to reduce water absorption and enhance... 

Acrylamide readily undergoes polymerization by conventional free radical methods, ionizing radiation, ultrasonic waves, and ultraviolet radiation. The base-cata-lized hydrogen transfer polymerization of acrylamide yields poly-/3-alanine (Nylon 3) a water insoluble polymer that is soluble in certain hot organics. All current industrial production is believed to be by free radical polymerization. 

The theory of radiation-induced grafting has received extensive treatment. The direct effect of ionizing radiation in material is to produce active radical sites. A material s sensitivity to radiation ionization is reflected in its G value, which represents the number of radicals in a specific type (e.g., peroxy or allyl) produced in the material per 100 eV of energy absorbed. For example, the G value of poly(vinyl chloride) is 10-15, of PE is 6-8, and of polystyrene is 1.5-3. Regarding monomers, the G value of methyl methacrylate is 11.5, of acrylonitrile is 5.6, and of styrene is >0.69. 

Polymer radicals can also be produced by the irradiation of a polymer-monomer mixture with ionizing radiation. Thus, the interaction of ionizing radiation with polyethylene-styrene produces radical centers on polyethylene, and these initiate graft polymerization of styrene to produce poly(ethylene-gra/i-styrene) [Rabie and Odian, 1977]. 

Fluorosilicone elastomers generally respond to ionizing radiation in a fashion similar to fhaf of silicone elastomers (polydimethylsiloxanes). One interesting application is a process of preparing blends of fluoroplastics, such as poly(vinylidene fluoride), with fluorosilicone elastomers to obtain materials having a unique combination of flexibility at low temperatures and high mechanical stiength. ... 

Ionizing radiation on poly(alkyl acrylates) results in cross-linking efficiencies, which are sensitive to the structure of the alkyl ester group."... 

In earlier work preformed polymer was cross-linked, e.g. by ionizing radiation (39, 103, 104) with suitable assumptions as to randomness of the reaction, the molecular statistics of product can be calculated as a function of the degree of cross-linking. An alternative method is to co-polymerize with small amounts of tetra-functional monomer, e.g. divinyl benzene (36, 105, 107). Both these methods produce highly poly-disperse products, having tetra-functional branch-points. 

Primary processes induced by ionizing radiation in the solution are excitation and ionization of the solvent molecules. Subsequent electron attachment to solute polymers leads to the formation of polymer anions. So far the radical anions of poly(methyl methacrylate) (PMMA) [46, 47], substituted PMMA [46, 47], poly(4-vinylbiphenyl) (PVB) [47-50], poly(l-vinylpyrene) (PVP) [50], organopolysilane [51] and substituted polyacetylene [52] have been studied. 

In carbon tetrachloride poly(a-methylstyrene) were degraded, even without oxygen, by the irradiation of ionizing radiation [58], The decay of the charge transfer radical complex, observed in this solvent, may be due to the reaction of a chlorine atom with p-site H of poly(a-methylstyrene) the reaction leads to the formation of P-position radicals of poly(a-methylstyrene). The produced polymer radicals were unstable and dissociated into neutral and radical species. 

Conditions selected so that the copolymer contained about the same amount of cellulose, 77-82% AN = acrylonitrile DMF = N,N-dimethylformamide. b Initial molecular weight of cellulose 7.1 X 105 for ionizing radiation molecular weight of cellulose was determined at dosage indicated no determination was made on possible oxidative depolymerization of cellulose by chemical redox systems. c Based on poly (acrylonitrile) recovered from acid hydrolysis of copolymer and on intrinsic viscosity method. 

Very little work has been reported on the effects of irradiation of PCTFE. One source claims that the resistance of PCTFE to ionizing radiation is superior to that of other fluoropolymers [42], Another work reports that poly(chlorotrifluoroethylene) degrades when exposed to ionizing radiation in a similar fashion as PTFE at ambient... 

To study the structural sensitivity of poly silanes to ionizing radiation, a number of samples were irradiated with a calibrated Co source, and the degraded materials were analyzed by GPC in a manner similar to that described for the determination of photochemical quantum yields (59). In radiation processes, the slopes of the plots of molecular weight versus absorbed dose yield the G values for scissioning, G(s), and cross-linking, G(x), rather than the respective quantum yields. These values, which represent the number of chain breaks or cross-links per 100 eV of absorbed dose, are indicative of the relative radiation sensitivity of the material. The data for a number of polysilanes are given in Table IV. Also included in Table IV for comparison is the value for a commercial sample of poly(methyl methacrylate) run under the same conditions. The G(s) value of this sample compares favorably with that reported in the literature (83). 

Sisman and Bopp, Charlesby, Turner and Petrov and Karpov studied the yield of total gas evolution from natural mbber, poly butadiene and various GR-S type copolymers subjected to ionizing radiation (reactor, Co or electron accelerator). Most of the gas is H2 + CH4 (100% in the case of polybutadiene), however for some rubbers a small amount of CO2 + C3H6 was found also. Turner found that under bombardment with accelerated electrons, the evolution of hydrogen from purified natural mbber was linear with dose, up to ISO megarads, and corresponded to G(H2) = 0.64. This radiolytic yield is noticeably smaller than those found in low-molecular-weight olefins. 

One of the most interesting problems was evaluation of quantum yield for light induced crosslinking of poly(vinyl butyral) in the presence of diphenyl sulphoxide. Mathematical treatment of the molecular changes produced in polymers by light is based on that by ionizing radiation. In our case, as the changes above the gel point were examined, the only suitable approach... 

---