Abstract
The comparison between physical properties and chemical structures of several polysiloxanes was studied at initial state and upon ageings. Techniques such as densimetry, gel permeation chromatography, FTIR spectroscopy, thermogravim- etric analysis coupled with IR spectroscopy and the new tool photo-DSC were used to give assessments of average mo- lecular weight, chemical evolution, cristallinity and thermal stability. Different types of ageing such as thermal ageing (60?C and 100?C), photo-ageing and acid vapour ageing were performed. After ageing we observed an evolution of chemical structures and physical properties for all samples. The main pathway of degradation is given for each sample. It results in oxidation, chain scission or cross-linking. Cross-linking levels are dependant on the type of ageing, the chemical structure and the initial rate of cristallinity. Cross-linking reactions are favoured after photo-ageing. Oxidation is higher for polysiloxane with aliphatic carbon chain.
Highlights
Polysiloxanes are often used as protective coatings for a variety of specialized applications
Techniques such as densimetry, gel permeation chromatography, FTIR spectroscopy, thermogravimetric analysis coupled with IR spectroscopy and the new tool photo-DSC were used to give assessments of average molecular weight, chemical evolution, cristallinity and thermal stability
Cross-linking levels are dependant on the type of ageing, the chemical structure and the initial rate of cristallinity
Summary
Polysiloxanes are often used as protective coatings for a variety of specialized applications. In the case of SiH-silicone, hydroperoxides are primarily formed and result from radical attack on the Si-H bonds. These unstable hydroperoxides are transformed essentially into silanols. When SiH groups are located at the end of the chain, the oxidation rate is fairly high probably because of good accessibility of the reactive groups [1]. PDMS formed by hydrosilylation reactions containing dimethylene and methine groups [2] have similar oxidation rates of vinylPDMS. The stability towards oxidation was confirmed and unexpected facility to cross-link upon ageing was detected
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