Scission, radiation-induced

Crystallinity has been studied by x-ray irradiation (85). An initial increase caused by chain scission in the amorphous phase was followed (above 3 kGy or 3 X 10 rad) by a gradual decrease associated with a disordering of the crystallites. The amorphous component showed a maximum of radiation-induced broadening in the nmr at 7 kGy (7 x 10 rad). 

Radiation-induced degradation reactions are in direct opposition to cross-linking or curing processes, in that the average molecular weight of the preformed polymer decreases because of chain scission and without any subsequent... 

These processes compete with radiation-induced crosslinking, scission and, for case (c), polymerization. 

The polymer TBSS is known to undergo radiation induced chain scission and provides an improvement in the sensitivity compared to resists formulated with polymers which do not undergo chain scission. The lithographic performance of a resist formulated from this polymer and 2,6-dinitrobenzyl tosylate acid generator is reported. 

Deep-UV resists comprised of matrix polymers and a 2,6-dinitrobenzyl tosylate photoactive acid generator have been described and compared to previously reported onium salt systems. Although these resists exhibited lower sensitivity than onium salt-based materials, the contrast and processibility are superior. The use of a matrix polymer capable of radiation-induced chain scission improves the sensitivity and allows the 2,6-dinitrobenzyl tosylate acid generator to more nearly... 

Figure 27. Mechanism of radiation induced chain scission in PMMA. Homolysis of the mainchain-carbonyl carbon bond is indicated as the initial step. Acylcarbon-oxygen, sigma bond homolysis also occurs but rapid decarbonylation ultimately leads to the same indicated products.

Creep rates of three glassy polymers are much greater during electron irradiation than before or after. Radiation heating is eliminated as a possible cause. Essentially the same concentration of unpaired electrons and ratio of cross-linking to scission were found in polystyrene samples in the presence or absence of stress. The effects of radiation intensity, stress, and temperature on creep during irradiation are examined. The accelerated creep under stress is directly related to a radiation-induced expansion in the absence of stress. This radiation expansion is decreased by increase in temperature or plasticizer content and decrease in sample thickness. It is concluded that gas accumulation within the sample during irradiation causes both the expansion under no stress and the acceleration of creep under stress. 

Table I. Possible Radiation Induced Bond Scissions in Poly (Isobutene Sulfone) and Expected Number of Lines in the ESR Spectra of the Corresponding Radicals...

C are given in Table IV. The relatively greater proportion of 1-butene from ethylene-hexene copolymers indicates that there are two mechanisms for the formation of the butenes, one involving the butyl branches and that this pathway yields a much higher proportion (perhaps 100%) of 1-butene. The C4 hydrocarbons are apparently also formed by fragmentation of chain ends in the polymers. These are probably formed mainly by radiation-induced scission. 

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