Poly irradiation, degradation

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... 

Heat stabilizers protect polymers from the chemical degrading effects of heat or uv irradiation. These additives include a wide variety of chemical substances, ranging from purely organic chemicals to metallic soaps to complex organometaUic compounds. By far the most common polymer requiring the use of heat stabilizers is poly(vinyl chloride) (PVC). However, copolymers of PVC, chlorinated poly(vinyl chloride) (CPVC), poly(vinyhdene chloride) (PVDC), and chlorinated polyethylene (CPE), also benefit from this technology. Without the use of heat stabilizers, PVC could not be the widely used polymer that it is, with worldwide production of nearly 16 million metric tons in 1991 alone (see Vinyl polymers). 

However, Pacansky and his coworkers77 studied the degradation of poly(2-methyl-l-pentene sulfone) by electron beams and from infrared studies of the products suggest another mechanism. They claim that S02 was exclusively produced at low doses with no concomitant formation of the olefin. The residual polymer was considered to be essentially pure poly(2-methyl-l-pentene) and this polyolefin underwent depolymerization after further irradiation. However, the high yield of S02 requires the assumption of a chain reaction and it is difficult to think of a chain reaction which will form S02 and no olefin. 

Temperature dependence (related to the temperature dependence of the conformational structure and the morphology of polymers) of the radiation effect on various fluoropolymers e.g., poly (tetrafluoroethylene-co-hexafluoropropylene), poly(tetrafluoroethylene-co-perfluoroalkylvinylether), and poly(tetrafluoroethylene-co-ethylene) copolymers has been reported by Tabata [419]. Hill et al. [420] have investigated the effect of environment and temperature on the radiolysis of FEP. While the irradiation is carried out at temperatures above the glass transition temperature of FEP, cross-linking reactions predominate over chain scission or degradation. Forsythe et al. [421]... 

Cheng et al. [116] reported that the structure of primaquine phosphate irradiated with 0.7—10 Mrad remained unchanged. The energy transfer action of the quinolyl group was considerable due to its resonance stabilization. Radiation-induced degradation of polyl(vinyl alcohol) decreased in the presence of primaquine phosphate but the degradation mechanism was unaffected. The content of primaquine phosphate showed linear relationship with degradation parameters of poly(vinyl alcohol). 

Qln YS, Ma QW, Wang XH, Sun JZ, Zhao XJ, Wang FS (2007) Electron-beam irradiation on poly (propylene carbonate) in the presence of polyfunctional monomers. Polym Degrad Stab 92 1942-1947... 

Pearson and Johns.81,138 Irradiated poly U was degraded by treatment with the enzyme pancreatic RNase. Three major photoproducts were isolated from the hydrolysis products and identified as Up, DpUp,... 

It is evident that most future work with irradiated polynucleotides will have to employ techniques such as these. Many pertinent observations were made about the effect of irradiation of the poly U upon enzyme specificity and rate. Irradiation of the polynucleotide drastically reduced the rate of hydrolysis of poly U by RNase. It was observed that RNase could not split the phosphodiester bond on the 3 -OH end of uridylic acid dimer. It was also shown that dehydration of irradiated poly U was accompanied by marked phosphodiester bond breakage and degradation of the polynucleotide. 

The yield of cross-links depends on the microstructure and purity of the polymer as well as whether it was irradiated in air or in vacuo2 The rate of degradation was found to be essentially zero when polybutadiene or poly(butadiene-styrene) was irradiated in vacuo, but increased somewhat when irradiated in air. 

Further evidence for specificity of C-S scission as the primary degradation reaction is provided by ESR. For example, Table I shows possible bond cleavages (A-E) in poly (isobutene sulfone) and the expected number of hyperfine lines in the ESR spectrum of the resultant radicals. The ESR spectrum observed after irradiation of poly (isobutene sulfone) at 77° is shown... 

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