Radiation-induced cross-linking

The rate of 7-radiation-induced cross-linking in the crystalline and amorphous regions of a crystallizable polychloroprene has been measured by Makhlis et al. [75] who have found a considerably lower cross-link density and less degradation in the crystalline portion of the rubber. The cross-links have been posmlated to be mainly intramolecular in crystalline regions and intermolecular in the amorphous phases. 

Radiation-induced cross-linking of chlorinated and chlorosulfonated high-density PE has been reported by Korolev et al. [262]. It has been observed that the extent of cross-linking is strongly dependent on the chlorine content in the sample, chlorosulfonated PE is cross-linked more readily than the chlorinated sample in air and inert atmosphere. 

Acceleration of Radiation-Induced Cross-Linking of Polyethylene by Chlorotrifluoroethylene... 

In the previous papers, we reported that the radiation-induced cross-linking of polyethylene was accelerated by acetylene (4) and by the mixtures of acetylene and some fluorine-containing monomers (5). 

Procedure. The radiation-induced cross-linking was carried out as follows. About 0.1 g of polyethylene film was placed in a glass ampoule of 30 mm diameter and 200 mm long. Gaseous CTFE and the mixture of CTFE/butadiene was introduced into the ampoule under the gas pressure of 1 atm. after evacuation of the ampoule. The ampoule was irradiated by Y-ray with a cobalt-60 at the dose rate of 0.05Mrad/hr at room temperature. 

Role of Unsaturated Group in the Cross-Linking in the Presence of CTFE. In order to make clear the role of unsaturated group contained in polyethylene, the radiation-induced cross-linkings of the polyethylenes containing various concentrations of the unsaturated groups were carried out in the presence of CTFE. 

Radiation-induced cross-linking of LDPE in the presence of various fluorine-containing monomers at a dose of 2.5 Mrad... 

Radiation-Induced Cross-Linking in the Presence of CTFE/Butadiene Mixture. On the basis of the results mentioned in the previous section, it is concluded that in the irradiation of polyethylenes in the presence of CTFE the polyethylenes are mainly cross-linked through the addition reaction of the unsaturated groups contained in the main and the side chains of the polymers to the propagating graft chain radical of CTFE. Therefore, the radiation-induced cross-linking of polyethylene is expected to be accelerated by the presence of the mixture of CTFE and a diene monomer effectively than the presence of pure CTFE. 

The radiation-induced cross-linking of polyethylenes in the presence of CTFE/butadiene mixture with various compositions are shown in Figure 6. The overall degree of co-grafting decreased gradually with the increase in the mole fraction of butadiene in the mixture, while the gel fraction of the polymer was increased rapidly by the addition of a small amount of butadiene to CTFE and then decreased with the increase in butadiene mole fraction in the mixture. The maximum of the gel fraction was found at about 0.1-0.2 of butadiene mole fraction in the mixture. 

If the number of radiation-induced cross-links exceeds the number of chain fractures, there is a net molecular weight increase if the degree of cross-linking is sufficiently high, an insoluble network is formed. Charlesby (6) gives a detailed treatment of these processes. 

Simic M, Dizdaroglu M (1985) Formation of radiation-induced cross-links between thymine and tyrosine Possible model for cross-linking of DNA and proteins by ionizing radiation. Biochemistry 24 234-236... 

Balabanovich AI, Zevaco TA, Schnabel W. Fire retardance in polyfbutylene terephthalate). The effects of red phosphorus and radiation-induced cross-links. Macromol. Mater. Eng. 2004 289 181-190. 

The formation of a polymer networks starts with an increase in molecular weight and formation of branched structures. At a typical extent of reaction, the gelation point is that point at which a network is first formed. The extent of reaction as well as the cross-linking density in radiation-induced cross-linking processes is determined by the radiation dose. The term dose means the quantity of radiation applied to or absorbed accidentally by a given volume or mass of sample. The absorbed dose is measured in Gray (Gy), 1 Gy = 1J kg-1. Therefore, the formation of a polymeric network needs a certain dose, the gelation dose Dg, which can be determined by sol-gel analysis. ... 

Henke A, Kadlubowski S, Ulanski P, Rosiak JM, Arndt KF (2005) Radiation-induced cross-linking of polyvinylpyrrolidone-poly(acrylic acid) complexes. Nucl Instrum Methods Phys Res B 236 391-398... 

Ulanski P, Pawlowska W, Kadlubowski S, Henke A, Gottlieb R, Arndt KF, Bromberg L, Hatton TA, Rosiak JM (2006) Synthesis of hydrogels by radiation-induced cross-linking of Pluronic F127 in NjO-saturated aqueous solution. Polym Adv Technol 17(9—10) 804—813... 

Scheme 5. Radiation-induced cross-linking polymerization of monofunctional (O) and multifunctional (U) monomer blends.

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