Silicone gels are prepared by curing elastomers in the presence of silicone oils and then used in a variety of applications, ranging from implantable devices to sealants for HEPA filters. Traditionally, linear silicone oils are used to prepare the gel but, over time, the oils are known to bleed from the gel into the surrounding environment. This can pose several problems including loss of viscoelasticity for sealants and potential implications for bleed from a biomedical device in vivo. Since the viscosity of linear polymers has been shown to increase by adding linear branches to the backbone,1 we are exploring the possibility that more elaborate branches of different architectures can be used to further increase the viscosity and in turn, cause the oil to be better retained within a gel. Linear silicone polymers bearing SiH functional sites of uniform molecular weight were prepared by equilibration with acid. A hydrosilylation reaction was used to functionalize the polymers with three different silicone side chains. The control sidechain, a linear polymer, was prepared using ring-opening polymerization. Two highly branched silicones were prepared using the Piers-Rubinsztajn (PR) reaction and a second generation, dendrimer-like side chain was prepared by alternating PR and hydrosilylation reactions (Scheme).2 The degree of branching with these distinct branched groups along the polymer backbone was varied. Residual SiH groups were capped with vinylpentamethyldisiloxane to prevent undesirable crosslinking into the network and the viscosities of the uncapped and capped materials were compared. Gels were synthesized with the capped oils. We will report on the viscosity properties and trends of the silicone oils as a function of frequency and size of branching, as well as our preliminary studies of their behaviour in gels. 1Charlesby. Polym. Sci. 1955, 17, 379-390. 2Grande et al. Polym. Chem. 2014, 5, 6728-6739.

Using highly branched silicone oils to tailor the properties of gels

251st National Meeting (2016)

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