Absorption polymer trapping

Absorption (Polymer Trapping, Solid-Phase Microextraction,... 

The haze can be attributed to several factors, such as particles dispersion, particles sizes embedded in film surface or polymer matrix, surface roughness due to large crystallite size, and wide variation in crystallite, presence of voids or pinholes, absorption or trapping of moisture, and so on [14]. There are a large number of defects involved in the structure and surface of materials, for this reason it is sometimes diflEcult to find the exact cause of haze. 

The excellent agreement between the TSC and P1A results has two implications. First, since the TSC method probes the product of mobility and carrier density, while the P1A probes only the carrier density, there seems to be no dominant influence of temperature on the carrier mobility. This was also found in other conjugated polymers like /ra/ry-polyacetylene [19, 36]. Second, photoconductivity (observed via the thermal release of photoexcited and trapped earners) and photo-induced absorption probe the same charged entity [36, 37J. 

The effect of antioxidants such as hindered phenohcs, secondary amine, and thioester on the radiation cross-linking efficiency of LDPE has been reported [260]. Amount of cross-linking at a given dose decreases with aU the antioxidants, the thioester being the most effective. IR absorption spectroscopy has been used to demonstrate dose-rate dependence of trani -vinylene unsaturation in irradiated Marlex 50 PE [261]. When the irradiated polymer is stored in vacuum a decrease is observed in trani-vinylene absorbance over a period of several weeks. After high dose-rate irradiation the decay is preceded by an initial increase. These phenomena have been ascribed to the reaction of trapped radicals. 

A second probable mode of free radical formation stems from the formation of C02 and CO—e.g., by Reaction 4. Even though G values for C02 and CO are relatively high (Table I), it is known from ESR studies that radicals such as those shown in Reaction 4 do not remain trapped in the polymer at room temperature. Presumably such radicals, being formed at a separation of only one or two atomic diameters, react readily in pairs. For example, the absorption band at 12.9 microns might be caused by the group formed by combination of the radicals formed by Reaction 4 (4). Possibly, a proportion of such radicals abstract... 

The es reacts with PVB to give a polymer anion with a high efficiency [47]. The rate constant was evaluated as 4.7 x 109 mol -1 dm3 s-1 in hexamethylphos-phorictriamide. The absorption specra of the radical anions of PVB [47] and PVP [48] are similar to those of biphenyl anion and pyrene anion, respectively, to mean that the excess electrons trapped by the polymers are essentially localized on the side groups. 

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