“<i>All-in-One</i>” Thixotropic Polysiloxane Pastes for UV-Activated Room Temperature Hydrosilylation Cross-Linking in Additive Manufacturing
James V. Beach, Shane C. Mann, Charles Ault, Dragana Radojčić, Xianmei Wan, Alisa Zlatanić, Steven Patterson, Jamie M. Messman, Petar R. Dvornić
Abstract
In search of “inks” for additive manufacturing of silicone rubber parts, three different types of “all-in-one” pastes with suitable rheological flow properties, ultraviolet (UV)-activated fast cross-linking by hydrosilylation in air at room temperature (as quick as 20–30 s), and shelf lives of over six months in the dark and 6–9 days in laboratory daylight, depending on paste composition, have been developed. The pastes are based on vinylsiloxy-functionalized, completely amorphous, linear terpolysiloxanes containing predominantly dimethylsiloxy-, DiMeS, repeat units with small amounts (typically less than 5 mol %), of diphenylsiloxy-, DiPhS, methylphenylsiloxy-, MePhS, or diethylsiloxy-, DiEtS, crystallization disruptors. The base polymers were compounded with trimethylsilylated hydrophobic silica fillers, thixotropic flow agents, hydrosilyl-functionalized oligomeric cross-linkers, and catalytic systems containing either platinum(II) acetylacetonate, Pt(AcAc)2, or trimethyl(methylcyclopentadienyl)-platinum(IV), MeCpPtMe3, and diethyl azodicarboxylate, DEAD, catalyst inhibitors. Paste preparation, steady and oscillatory shear rheology, and UV-activated cross-linking and shelf-life stabilities are described.