L. N. Pankratova

Radiation-chemical processes in polyorganosiloxanes

Radiation-induced changes in polymethylphenylsilsesquioxane block copolymers were studied. It was found that a pregel was formed at doses of 30–50 kGy and gel formation mainly occurred in polydimethylsiloxane (PDMS) blocks. The UV spectrophotometry of samples in a cyclohexane solution demonstrated that, at doses of 10–50 kGy, a noticeable broadening of absorption bands due to phenyl groups was observed only in oligophenylsilsesquioxane and not in the block copolymers. Hydrogen atoms formed in the radiolysis of PDMS did not reach polyphenylsilsesquioxane blocks.

Effect of Aromatic Protectors on the Radiolysis of Polyorganosiloxanes

The influence of phenyl and other aromatic groups on radiation crosslinking of polydimethylsiloxane and its mechanical blends and copolymers with polydiphenylsiloxane and polyphenylsilsesquioxane, radiation-induced gas evolution, and radical generation in these systems were considered. It was shown that radiation-chemical yields of crosslinking and gas evolution follow a simple exponential law over a wide concentration range of phenyl groups (at their content above 1 mol %). A similar dependence was observed for the radiation-chemical yield of hydrogen in ethylene copolymers with styrene. For the crosslinking processes, it was proved that the effect of phenyl groups is identical in the mechanical blends and copolymers of polyorganosiloxanes. The effect of retardation of radiation-chemical processes by phenyl groups was shown to be independent of whether one or two groups is linked to a silicon atom, it is their total amount that matters.

Effect of Radiation on the Supermolecular Structure of Siloxane Block Copolymers with Different Compositions and Block Sizes

Abstractγ-Radiation-induced changes in the supermolecular structure of dimethylphenylsilsesquioxane block copolymers were studied with the use of electron microscopy. It was found that the supermolecular structure of the block copolymers was altered by irradiation. The character of changes depends on the size of a soft, dimethylsiloxane block, as well as on the total amount of the blocks in the copolymer molecule. A variation in the properties of block copolymers upon γ-irradiation was also detected by the technique of differential scanning calorimetry.

Effect of irradiation on siloxane block copolymers at doses below 100 kGy

A study of radiation-induced changes in polydimethylphenylsilsesquioxane block copolymers demonstrated that the impurities of dimethylcyclosiloxanes (Dx) that are formed in the synthesis of block copolymers disappeared at doses of 10–50 kGy. An increase in the dynamic viscosity (by a factor of 2–3) of 20: 5 and 20: 10 block copolymers irradiated at 50 kGy suggests that the formation of ≡Si-CH-CH2-Si≡ bridges was not solely responsible for a structural rearrangement in the block copolymers. The rheological characteristics of the block copolymers changed under irradiation because of the transformations and interactions of Dx with the matrix.

SPECTRAL MANIFESTATIONS OF PARTIAL SILICON-OXYGEN DOUBLE BOND CHARACTER IN OLIGOPHENYLSILOXANES

Conclusions1.We have considered the UV and IR spectra of a number of oligophenylsiloxanes with different structures.2.The data obtained have been discussed in light of the concept of partial double bond character for Si and O atoms in the siloxane chain.