Chain‐End and Chain‐Internal Crosslinking in “Latent Reactive” Silicon Elastomers

Abstract

Summary: Latent reactivity has been employed to create processable elastomers constructed of carbosilane and either carbosiloxane or polyether segments. Two types of latent modes have been introduced: “chain‐internal” and “chain‐end” sites through the use of labile silicon methoxy and trifunctional olefinic functionalities. These latent reactive sites remain inert during formation of the linear copolymer; subsequent exposure to moisture triggers hydrolysis of the methoxy group and formation of a chemically crosslinked thermoset. These “chain‐end” sites limit the formation of dangling chains improving the overall mechanical properties of the material. The thermoset's mechanical response can be potentially varied from plastic to elastic behavior, depending on the ratio of hard and soft monomers employed. The concentration of “chain‐internal” and “chain‐end” crosslink sites enhances strength; modification to the run length and structure of the soft phase enhances elasticity, generating samples having moduli of 6 MPa, tensile strengths of 0.6 MPa and elongations of 400%.“Latent reactive” silicon elastomer.magnified image“Latent reactive” silicon elastomer.

Thermally crosslinked carbosiloxane and oligo(oxyethylene) polymers

“…The use of monofunctionalized chain end-capping monomer 2 (synthesized by a Grignard reaction of 10-undecenylmagnesium chloride 1-chloro-1-methylsilacyclobutane) facilitates further processing by limiting molecular weight, and decreases the number of dangling chains in the final thermoset polymer. 13 The resulting silacyclobutane endcapped oligomers 4a-b and 5a-b were characterized by IR, 1 H-NMR, and 13 C-NMR. Molecular weights were determined by GPC, and thermal behavior was measured by DSC and TGA.…”

“…The reaction flask was then placed in a 50 C oil bath and high vacuum (\0.01 mmHg) was applied over 72 h. The reactions were quenched by exposure to the air. Full characterization ( 1 H-NMR, 13 C-NMR, GPC results versus PS, and TGA) details are given in the Supporting Information for the unhydrogenated polymers.…”

“…Full characterization ( 1 H-NMR, 13 C-NMR, GPC results versus PS, and TGA) details are given in the Supporting Information for the hydrogenated polymers.…”

“…This led to an improvement in the mechanical properties, reflected in a modulus of 6 MPa, and a percent elongation of 400, both comparable to properties of commercial elastomers. 13,14 While the improvements were encouraging, it was clear that hydrolytically driven crosslinking has disadvantages in intrinsically hydrophobic materials. Consequently, we turned to other types of latent crosslink reactions, specifically those driven by exposure to high temperature.…”

Novel polymethoxylsiloxane‐based crosslinking reagent and its in‐situ improvement for thermal and mechanical properties of siloxane elastomer

“…The alkoxy groups could react with atmospheric moisture. 23 This may help to produce polysiloxane with rich pendant reactive groups as room temperature crosslinking sites.…”