Effect of Molecular Weight on the Cross-linking of Siloxanes by High-energy Radiation

Nature ◽  
1954 ◽  
Vol 173 (4406) ◽  
pp. 679-680 ◽  
Author(s):  
A. CHARLESBY
Keyword(s):  
Molecular Weight ◽  
High Energy ◽  
Cross Linking ◽  
High Energy Radiation ◽  
Energy Radiation ◽  
The Cross

Changes in silicone polymeric fluids due to high-energy radiation

1955 ◽  
Vol 230 (1180) ◽  
pp. 120-135 ◽  
Keyword(s):  
Molecular Weight ◽  
Radiation Dose ◽  
High Energy ◽  
Cross Linking ◽  
Polymeric Fluids ◽  
High Energy Radiation ◽  
Energy Radiation ◽  
Hydrocarbon Polymers ◽  
Amorphous Structures ◽  
The Relationship

When subjected to high-energy radiation, polydimethyl siloxanes can be cross-linked to form insoluble amorphous structures which are transparent and have marked rubber-liko properties. Data are given on the relation between molecular weight and bulk viscosity, which is often used to characterize these polymers. The relationship between cross-linking density and radiation dose is deduced from the changes in both solubility and fusibility, and is confirmed by elastic measurements. Unit pile radiation is found to produce cross-linking in about 2*2 % of the monomer units. Details are given of the change in solubility and swelling with radiation dose and of the mechanism of cross-linking. The energy per cross-link is about 32 eV, and is independent of molecular weight. A brief comparison is made with cross-linking in hydrocarbon polymers.

The Cross-Linking of Rubber by Pile Radiation

1955 ◽  
Vol 28 (1) ◽  
pp. 1-11
Author(s):  
Arthur Charlesby
Keyword(s):  
Molecular Weight ◽  
Radiation Dose ◽  
Average Molecular Weight ◽  
High Energy ◽  
Cross Linking ◽  
Gel Formation ◽  
Gel Fraction ◽  
Cross Links ◽  
The Cross ◽  
The Relationship

Abstract The degree of cross-linking produced in a rubber by high-energy radiation is proportional to the radiation dose. Unit radiation, as defined in the text, links 1.1 per cent of the isoprene units. The distribution of molecular weight prior to cross-linking agrees with a Poisson distribution. Gel formation begins for γ=0.5. From the radiation dose required to initiate gel formation, the initial average molecular weight can be deduced. The increase of gel fraction with radiation dose follows the relationship deduced theoretically in the first part of the article. Measurement of gel fraction gives an alternative method of calculating the initial average molecular weight. Where some cross-linking is present in the rubber prior to cross-linking, this may be evaluated. In accordance with the theory presented in the article, the viscosity of the sol fraction rises initially, then decreases as the radiation dose increases. This provides a third method of measuring molecular weight, or of relating viscosity to molecular weight, which can be deduced from measurement of gel fraction. The swelling of very lightly cross-linked gel has been compared with the Flory-Huggins relationship, which is found to hold down to very lightly cross-linked gels for which the cross-linking index is only 0.2. To obtain this agreement, it is necessary to consider the swelling of the dry gel, rather than the whole specimen, and to ignore the cross-links required to form the gel itself.

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