Photoplasticity is a phenomenon wherein the shape of crosslinked polymers, under stress, can be induced to change by irradiation with light. Photoplasticity in crosslinked polymer systems via stress relaxation has been reported in polyether-acrylate thiol-ene polymer systems by incorporating allyl thioether functionality by ring-opening copolymerization with 6-methyl-3- methylene-1,5-dithiacyclooctane (MDTO). The object of the present work is to adapt the photoplastic stress relaxation approach to demonstrate shape change in silicone elastomers. The apparent way to achieve this is end is to replace the polyether-acrylate thiol-ene monomers, employed in the published literature, with multi-functional silicone-thiols and alkenyl endfunctional siloxanes chain extended with MDTO. While homogeneous amorphous elastomeric siloxane-based thiol-enes are well known, it was found that copolymerization of MDTO with the thiol-ene siloxane monomers leads to formation of stable heterogeneous polymer emulsions. Such behavior of thiol-ene siloxanes in the presence of MDTO was found to be a result of the tendency of MDTO to homopolymerize and incipient immiscibility in solutions of MDTO and functionalized siloxane oligomers. The nature of the emulsion formed and extent of crosslinking can depend on factors such as the reactivity of the alkene, the nature of the thiol component and the type of initiation process used. Given that the ring-opening of MDTO was initiated from the multifunctional siloxane thiol, the degree to which chemically different dialkenyl siloxanes were incorporated in the reaction was investigated. Irrespective of the reactivity of the alkene, homopolymerization of MDTO and formation of heterogeneous emulsions and gels always resulted when either the thiol, the ene or both were derived from siloxane oligomers.
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School of Chemistry and Materials Science (COS)
Pawar, Siddhesh, "Synthesis and characterization of photoplastic siloxane based thiol-ene polymer systems" (2008). Thesis. Rochester Institute of Technology. Accessed from
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