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.
Highlights
Condensation curing silicone elastomers are commonly used as protective coatings and sealants [1,2,3,4,5]
The condensation reaction allows efficient curing in ambient environment, which represents a significant advantage over silicone elastomers prepared by addition, radical, or UV
In our previous study [10], we showed that an inappropriate choice of the network formulation significantly compromises long-term elastomer stability such that the elastomer’s properties change continuously over time
Summary
Condensation curing silicone elastomers are commonly used as protective coatings and sealants [1,2,3,4,5]. In our previous study [10], we showed that an inappropriate choice of the network formulation significantly compromises long-term elastomer stability such that the elastomer’s properties change continuously over time (the study was terminated after 6 months, at Molecules 2021, 26, 82 at which time changes were still being observed) Several factors, such as cross-linker volwhich time changes were still being observed). Constitute the largest obstacle towards developing stable silicone elastomers with reproThis is material because of their volatility, causesofthe curing to become highly dependent on ducible performance. Thiswhich is because their volatility, which causes the curing both sample dimensions and the surrounding environment.
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