Silicon Nanoparticles as Solid-State Inhibitors for Methacrylic Autopolymerization

Polymerization inhibitors are added to methacrylic monomers to extend their shelf life and often need to be removed prior to use by means of tedious procedures. We report that hydrogen terminated silicon nanoparticles (H-SiNPs) inhibit thermal polymerization of methyl methacrylate (MMA) and allyl methacrylate (AMA) at temperatures as high as 100 °C [1]. As <i>solid-state </i>inhibitors, H-SiNPs are advantageous because they can be readily separated from the monomer by centrifugation and/or filtration. The reaction MMA and AMA in the presence and absence of H-SiNPs at various temperatures were explored using NMR and FTIR spectroscopy. In the presence of Si-H surface groups, methacrylic dimers form as a by-product of inhibition. Additionally, monomers attach to the surface of SiNPs through hydrosilylation of the methacrylic group, forming robust Si-C linkages that are resistant to hydrolysis. In the case of AMA, thermal hydrosilylation enables facile synthesis of free-standing vinyl terminated SiNPs. Catalytic hydrosilylation of H-SiNPs with AMA is being investigated using Kardsted’s catalyst (KC). Whereas KC has been extensively utilized for cross-linking of polysiloxanes [2], its effectiveness in facilitating hydrosilylation of olefins with H-SiNPs has not been methodically studied. Preliminary data show that MMA and AMA undergo hydrosilylation through the methacrylic group when high loadings of KC are used, in neat monomer or with toluene as solvent. The effect of solvent is being explored as a means to bias hydrosilylation selectively towards the vinyl group of AMA. This would enable methacrylate-capped free-standing SiNPs with potential applications in photocrosslinkable silicon formulations.<br/><br/>1. Golvari, P., K. Alkameh, and S.M. Kuebler, <i>Si–H Surface Groups Inhibit Methacrylic Polymerization: Thermal Hydrosilylation of Allyl Methacrylate with Silicon Nanoparticles.</i> Langmuir, 2022, in press.<br/>2. Hofmann, R.J., M. Vlatković, and F. Wiesbrock, <i>Fifty years of hydrosilylation in polymer science: a review of current trends of low-cost transition-metal and metal-free catalysts, non-thermally triggered hydrosilylation reactions, and industrial applications.</i> Polymers, 2017. <b>9</b>(10): p. 534.