Spectroscopic Signatures of MQ-Resins in Silicone Elastomers

Abstract

Polysiloxane elastomers have a large application space due to their versatile cross-linking chemistry and highly tunable physical and mechanical properties. One approach for improving the mechanical integrity of commercial polysiloxane “silicone” elastomers while maintaining their optical transparency is the addition of small, silicone-resin molecules to the network. However, both the poly­(dimethylsiloxane) (PDMS) network and the silicone-resin particles have an amorphous structure and complex chemistry, which makes the characterization of their structural properties and segmental network dynamics difficult. Here, we report the synthesis and characterization of a series of model silicone networks modified with a specific class of silicone-resin known as MQ-resin using Raman and advanced nuclear magnetic resonance (NMR) spectroscopy methods. Raman spectroscopy was successfully used to quantify the contribution of the MQ-resin to the network, to determine the type of MQ-resin present in the network, and to investigate the completeness of the network cross-linking reaction. Solid-state and 1H double-quantum (DQ) NMR spectroscopies were used not only as a detection method for the MQ-resins but also to quantify changes in the segmental dynamics of the network as a function of MQ-resin concentration. The combination of Raman and NMR spectroscopies describes a series of samples where the MQ-resin particles and PDMS chains maintain their independent segmental dynamics up to high concentrations of MQ-resins (40–50% MQ), where the physical properties of the resin dominate the physical properties of the overall network. The results from our spectroscopic analyses are consistent with the results from macroscopic characterization techniques such as solvent uptake and mechanical testing. The spectroscopic insights into the structure–property relationships of PDMS-MQ composites presented in this study are a valuable tool not only for the synthesis and reverse engineering of future generations of commercial silicone elastomers but also for understanding the mechanisms of aging and degradation over the material lifetime.

Preparation and Properties of PDMS elastomer cross-linked with hydrolyzate of TEOS, HEDS, or OETS oligomers: influence of cross-linker structure

“…No soluble fraction was detected in the swelling test, which validates that all PDMS CLs underwent reaction and crosslinking. The degree of swelling is inversely proportional to the extent of cross-linking; as the cross-linking degree increases, the swelling degree diminishes [11,[39][40][41]. As the content of CL increased, there was a corresponding decrease in the swelling degree.…”

Bio-based epoxy functionalized MQ silicone resins: from synthesis to toughened epoxy composites with good mechanical properties, thermal resistance and transparency

“…MQ silicone resins, as a branch of polysilsesquioxanes, feature a double-layer compact globular molecular structure, comprised of monofunctional silane units (M, R 3 SiO 1/2 ) and tetrafunctional silane units (Q, SiO 4/2 ). 17–19 The typical approach for synthesizing MQ silicone resins involves the hydrolysis and condensation of Si(OEt) 4 (Q unit) and Me 3 SiCl (M unit) under acidic or alkaline conditions. 20 The methyl groups of the M units could also be replaced by hydrogen and functionalities such as vinyl and phenyl.…”

True Molecular Composites: Unusual Structure and Properties of PDMS-MQ Resin Blends

“…An improvement of the cross-linking of the matrix with silica filler particles could be achieved by the use of bioinspired silica [ 35 , 36 ], polyhedral oligomeric silsesquioxane cages with vinyl groups linked to a central siloxane core by hydrosillylation [ 37 ] or MQ copolymers, where M is mono-, Q is tetrafunctional silicon units [ 38 , 39 , 40 ]. It was established [ 41 ] that MQ species have multiple chemical junction points in the silicone network, both covalent bonding and potential noncovalent interactions such as van der Waals, electrostatic or hydrogen bonding. Ultimately, the dynamics of polymer-filler interactions and their influence on mechanical and thermal properties is of utmost importance for understanding and predicting the lifetime and aging of silicone components.…”