Chain scissioning test

What will radiation during a test do to the stress relaxation of an elastomeric material if the radiation brings about chain scission Compare a cross-linked polymer with a high-molecular-weight uncross-linked one. 

Thus, radiation causes degradation, chain scission and further crosslinking. To distinguish between chain scission, crosslinking and degradation products, sorption/desorption studies were conducted. Selected specimens of 73/27 and 80/20 TGDDM/DDS were allowed to absorb acetonitrile to equilibrium. The acetonitrile was desorbed, and the samples were tested. 

Oxidation during processing of polypropylene is principally accompanied by chain scission made evident by a reduction in melt viscosity. The oxidation during processing of polyethylene on the other hand is accompanied mainly by crosslinking. The following two tests are, therefore, used ... 

Finally, the effect of ordering processes must be considered in the interpretation of results from accelerated aging tests. The activation energies for the chain-scission reaction and for molecular ordering are likely to be quite different. Furthermore, enhancement of the ordering process through the reduction in DP caused by chain scission is likely to manifest itself as an autocatalytic effect wherein the rate of decay of... 

As one might expect, a different picture emerges for the thermooxidative stability as reflected in the results of TO and ITG tests performed in air. The participation of oxygen in the overall degradation process leads to the intermediacy of imidazole free radicals and oxygenated free radicals with concomitant chain scission and the net result is a rather catastrophic weight loss observed as the test temperature approaches the 450-500 C level. The representative TG thermograms of Hg. 7, obtained in air, Dlustrate this trend... 

The ultimate test of usefulness is, of course, the lithographic performance of a resist. The often-quoted sensitivity of PMMA of 50 pC/cm2 assumes conventional developing conditions and is measured by competitive dissolution rates of exposed and unexposed films. A secondary measure of sensitivity for positive-working resists is the G(s) value, the yield of chain scissions per 100 e.v. of absorbed energy. In this case, mea-... 

Mechanical tests, molecular weight, and solubility measurements on irradiated PMMA/SAN blends showed that phenyl substitution in one of the polymers can offer partial radiation protection to the other component. Protective effects of the phenyl group are short range and occur only in miscible blends where mixing at the molecular level exists. However, the protection is not complete since some 15% of the yield for main chain scission in PMMA could not be suppressed, even at high styrene (in SAN) concentrations. 

---