Reliable Condensation Curing Silicone Elastomers with Tailorable Properties

Abstract

The long-term stability of condensation curing silicone elastomers can be affected by many factors such as curing environment, cross-linker type and concentration, and catalyst concentration. Mechanically unstable silicone elastomers may lead to undesirable application failure or reduced lifetime. This study investigates the stability of different condensation curing silicone elastomer compositions. Elastomers are prepared via the reaction of telechelic silanol-terminated polydimethylsiloxane (HO-PDMS-OH) with trimethoxysilane-terminated polysiloxane ((MeO)3Si-PDMS-Si(OMe)3) and ethoxy-terminated octakis(dimethylsiloxy)-T8-silsesquioxane ((QMOEt)8), respectively. Two post-curing reactions are found to significantly affect both the stability of mechanical properties over time and final properties of the resulting elastomers: Namely, the condensation of dangling and/or unreacted polymer chains, and the reaction between cross-linker molecules. Findings from the stability study are then used to prepare reliable silicone elastomer coatings. Coating properties are tailored by varying the cross-linker molecular weight, type, and concentration. Finally, it is shown that, by proper choice of all three parameters, a coating with excellent scratch resistance and electrical breakdown strength can be produced even without an addition of fillers.

Reactivity of Polysilazanes Allows Catalyst‐Free Curing of Silicones

“…As is common for condensation curing silicone systems, there is a long-term post curing effect, where any residual hydrides or hydroxyls will condensate and increase the density of the network. [36] An interesting behavior in the storage Scheme 3. Cross-linking reaction of PSz and carbinol silicones forming silicone networks by activated condensation.…”

“…As is common for condensation curing silicone systems, there is a long‐term post curing effect, where any residual hydrides or hydroxyls will condensate and increase the density of the network. [ 36 ] An interesting behavior in the storage modulus ( G ′) was observed for 5 and 7 wt% PSz, which showed a two‐stage curing process irrespective of curing temperature. This behavior is not seen in conventional curing of silicone and we suggest that this could be explained by the curing mechanism itself.…”

Silicone‐based polymer blends: Enhancing properties through compatibilization

“…In principle, many functionalization reactions are available to prepare polysiloxanes with an array of architectures and well‐defined chain ends, including hydrosilylation, thiol–ene, halogen substitution, and esterification 7 . Additionally, recent developments based on the Piers‐Rubinsztajn, aza‐Michael, condensation and azide‐alkyne click reactions provide a wide scope of orthogonal chemistries to create precise siloxane small molecules, polymers and networks 66–72 . Although a variety of methods to modify polysiloxanes exist, 57,62,63,65–73 the hydrosilylation of Si–H‐containing PDMS is by far the most versatile, allowing for efficient coupling to olefins, carbonyl groups, and other functionalities 73 .…”

“…Additionally, recent developments based on the Piers‐Rubinsztajn, aza‐Michael, condensation and azide‐alkyne click reactions provide a wide scope of orthogonal chemistries to create precise siloxane small molecules, polymers and networks 66–72 . Although a variety of methods to modify polysiloxanes exist, 57,62,63,65–73 the hydrosilylation of Si–H‐containing PDMS is by far the most versatile, allowing for efficient coupling to olefins, carbonyl groups, and other functionalities 73 . Indeed, this highly effective toolbox has enabled the development of various vulcanization strategies for the industrial production of silicone networks 58 .…”

A Silicon‐Stereogenic Silanol ‐18O‐Isotope Labeling and Stereogenic Probe Reveals Hidden Stereospecific Water Exchange Reaction

“…In addition, especially Si-chiral silanols could serve as an efficient chiral probe, providing new insights into downstream processes such as silanol condensation, which would be useful for silicone and siloxane material chemistry to optimize and synthesize improved products. [14] In the past, the concept of using chiral silanes as mechanistic probes has been demonstrated successful regarding other systems. [15][16][17] However, the preparation of Si-chiral compounds has proven challenging in the past due to limited access to suitable prochiral or chiral precursors.…”