Preirradiation dose

Figure 1. Influence of preirradiation dose of poly (vinyl chloride) films in vacuo on the extent of grafting observed after heating in methyl methacrylate at 50°C. for 1 hr, (Curve 1) and 2 hrs. (Curve 2) (5)...

Figure 2. Influence of preirradiation dose of polyethylene films in air on the rate of grafting observed on heating at 135°C. in acrylonitrile (2)...

For low radiation doses, peroxides accumulate almost linearly with dose. However, after a certain dose has been reached, their concentration tends to level off. This conclusion can be derived from the observed change in the rate of graft copolymerization initiated by polymers subjected to increasing doses of preirradiation in air. Figure 2 illustrates this effect in the case of grafting acrylonitrile onto polyethylene (2). The drop in the yield of peroxide production presumably results from the efficient radiation-induced decomposition of these peroxides. Peroxides are known to decompose under free radical attack, and selective destruction of peroxides under irradiation has been established experimentally (8). This decomposition can become autocatalytic, and sometimes the concentration of peroxides may reach a maximum at a certain dose and decrease on further irradiation. Such an effect was observed in the case of poly (vinyl chloride). Figure 3 shows the influence of preirradiation dose on the grafting ratio obtained with poly (vinyl chlo-... 

Figure 8. T emporal and spatial display of typical temperature profiles of a BC + Cl 2 reaction wave at (A) 77 K and (B) 4.2 K. Preirradiation dose 27 kGy.

Analogous results have been obtained with thin films of equimolar SOz solution in isoprene. When the surface of such a film immersed in liquid nitrogen was damaged with a thin needle, a copolymerization wave occurred which spread over the sample. The preirradiation dose required to excite the autowave process in this system was 200 kGy, which is also well above the critical values for cylindrical samples. 

Finally, difference of ion induced degradation between PMMA and PET is also seen from die different evolution of the overall secondary ion yield with the preirradiation dose. Chain scission has been reported to be induced for PMMA (12) when crosslinking proceeds during the ion irradiation of PET (13). Moreover, reference to crosslinking has already been used to explain the decrease of secondary ion yield after ion bombardment (7) this may explain the greater decrease of the secondary ions intensity observed for PET, compared to PMMA. 

T. Momose, H. Yoshioka, I. Ishigaki and J. Okamoto, Radiation drafting of a,a,(3-trifluorostyrene onto poly(ethylene-tetrafluoroethylene)film by preirradiation method. I. Effects of preirradiation dose, monomer concentration, reaction temperature, and film thickness, J. Appl. Polym. Sci., 1989, 37, 2817-2826 II. Properties of cation exchange membrane obtained by sulfonation and hydrolysis of the grafted film, 1989, 38, 2091-2101 III. Properties of anion exchange membrane obtained by chloro-methylation and quatemization of the grafted film, 1990, 39, 1221-1230. 

Preirradiation Dose and Reaction Time Used to Synthesize the Films with Various Grafting Percentages, Degree of Swelling of the Grafted Films at 25°C for 1 h in Water and Friction Coefficient Values of Swollen Grafted Films... 

Fig. 4 Grafting kinetics as a function of preirradiation dose (grafting conditions FEP 25 Jim, 50% monomer concentration in isopropanol, 10% DVB, 60 °C) [76]...

The order of dependence, determined as 0.64 for styrene grafting into EEP [72], 0.58 for grafting of acrylic acid into FEP [82], and 0.53 for styrene-acrylic acid [83], is in agreement with the theoretical value of 0.5 for free radical polymerization. Momose et aL [70] reported that for the grafting of a,P,fl-trifluorostyrene (TFS) into ETFE, the grafting rate and final percent grafting increase with increasing preirradiation dose, with the dose exponent... 

Fig. 8 Variation of DG with reaction time for styrene grafting into the PTFE films crosslinked with gamma rays at different doses (15 kGy preirradiation dose for the grafting reaction) [128]...

Fig. 13 a Stress-strain curves for pristine FEP and grafted films with different DG. b Elongation at break of grafted films as a function of DG, preirradiation dose, and type of solvent FEP 25 xm, 10% DVB in solvents toluene, isopropanol ( PrOH), isoprop anol/water mixture ( PrOH/water), and sodiumdodecyl sulfate/water (SDS/water) [76]... 

PTeOX prepared at various preirradiation doses in the range between 0.1 and 30 kGy shows double endothermic profiles, though T, and Tj2 decrease rather significantly with increasing dose, indicating a comparatively larger area of the endotherm at a lower temperature side. 

The effects of atmosphoe during polymoization and of prdrradiation dose are rather clear in the melting behavicr, but not clear in the X-ray difffacticm behavior mentioned in Secticm 2. The orientation of the polymer chains is not affected by atmosphere nor preirradiation dose only the polymer chain loigth is affected. 

In the case of preirradiation with Co y-rays, the effects of reaction time, dose and temperature in preirradiation grafting of styrene onto PHB have been investigated in detail. The degree of grafting X increased with the preirradiation doses of up to 15kGy and temperatures up to 80°C (Fig. 6.3) [61]. 

FIGURE 6.3 Effect of temperature in the graft reaction of styrene onto PHB surface with a preirradiation dose of 5kGy ( ) 30°C, (O) 50°C, (A) 70°C, ( ) 80°C. Reproduced with permission from Ref. [61]. Wiley-VCH Verlag GmbH Co. KGaA. 

MetaHoelement complexes may be useful for the post-irradiation treatment of radiation injury, based on the observation that several of these compounds accelerate recovery of, among other things, lympho/hemopoiesis. Preirradiation Mn2(0)(DIPS)g increases the survival of y-irradiated mice (103). Treatment of mice that have been exposed to an LD q q dose of y-rays plus Mn2(0)(DIPS)g either 1 or 3 h after irradiation also increases survival, which supports the hypothesis that this compound is an effective radiorecovery agent (105). Again, this increase in survival may result from the resynthesis of radiation-depleted Mn-dependent enzymes that facHitate the recovery of immunocompetence and tissue repair, as reported for Cu(II)2(DIPS)4. 

Bunte salts have bacterial, insecticidal, and fungicidal properties, and are also used as chelating agents (qv) or surfactants (qv) (97,98). Bunte salts have been tested for preirradiation protection for mammals exposed to lethal radiation doses (99,100) (see Radioprotectiveagents). 

Experiments were therefore performed in which crystalline acrylonitrile was preirradiated to a certain dose at -196 and... 

Figure 8. Creep in poly (vinyl chloiide) under a stress of 1442 p.s.i.g. at 57°-60°C. Stress applied after different times of preirradiation 1-2, 10, 15, and 50 minutes for Curves 1, 2, 3, and 4, respectively. Total dose to Curve 7 exceeds all doses delivered in Curves 1-4 (11)...

Table III. Effect of Dose Rate on Grafting of Preirradiated...

The microphotographs of Fig. 1 la and b demonstrate the brittle fracture of a film occurring in response to an impact at the point A (the initial state— frame a) with a needle, developing a pressure of 108 Pa for the time 0.1 s. Frame b shows that the impact produces a network of cracks in the grain affected. An analogous effect on a film preirradiated with a supercritical dose of y-rays initiates a traveling wave of chemical conversion (Fig. 17e) similar to those described in Section VIII. 

Irradiation. Irradiation was conducted in a Co source at a dose rate of about 4 X 10 rep per hour. Preirradiated starch was prepared by irradiation of starch under vacuum in a tube fitted with a break-off tip. The monomer was added to the tube after irradiation and freed from air, using the freeze-thaw technique. Then the tube was sealed and the tip broken, thus allowing the monomer to saturate the starch. For starch irradiated in the presence of monomer, the materials were thoroughly mixed, charged to a tube, evacuated using the freeze-thaw method, and immediately irradiated. 

Figure 4 shows results of grafting acrylonitrile to preirradiated as is starch. Increasing the total dose from 8 to 16 Mrep slightly increases the amount of grafting, and increasing the reaction temperature from 25° to 60° C. approxi-... 

It seems unlikely that the presence of S alone might create any particular effect. Moreover, the authors have experimentally shown that the disintegration products of the and the total amount of beta radiation received by the catalyst did not exert any influence. The latter point has also been confirmed in the above mentioned American study (46) where it is shown that preirradiation of the catalyst with a 10 e.v. g. gamma dose does not modify the catalytic activity. 

Thermal decompositions of barium and strontium azides, preirradiated with 1 MeV gamma rays, were conducted by Prout and Moore [78,79]. With dehydrated barium azide a total gamma dose of 20 Mrad (2.24 X 10 R) eliminated the induction period and increased the acceleration of the decomposition. A somewhat greater effect was evidenced with strontium azide. Avrami et al. [80] subjected barium azide to Co gamma radiation to exposure levels up to 1 XIO R (Table XIII). Differential thermal analyses (Figure 16) showed a steady decomposition of the sample, and after 1 X 10 R exposure (W hr at room temperature), infrared analysis indicated that the residue was in the form of barium carbonate. 

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