There is a growing demand for UV-photocurable silicones for use as coatings and adhesives. UV-radical cure chemistry also provides a convenient method to form covalently bound silicone-organic networks. These hybrid materials can be used to enhance properties such as adhesion or toughness versus traditional silicone polymers. In this work, we discuss fabrication of PDMS/PMMA hybrid elastomers through two synthetic routes – a one-step method that relies on copolymerization of MMA monomer with MMA-terminated PDMS, and a two-step method where MMA is swollen into a pre-cured PDMS network and subsequently polymerized. These routes both result in dispersed phases of PMMA inside a continuous PDMS matrix, but the two-step method creates a semi-interpenetrating network of PMMA in PDMS and the one-step method results in a random PDMS/PMMA copolymer that is crosslinked through the PDMS. The bulk modulus of both material types scales similarly when the PDMS/PMMA ratio is varied, from ~1 MPa at 100% PDMS to ~50 MPa at 50% PDMS, with significant enhancements in fracture toughness as PMMA content increases. Materials were characterized using SAXS, AFM, DSC, TGA, and GPC to better establish structure-property relationships. Though bulk properties are similar, the different network structures were found to significantly impact the PDMS glass transition temperature, the PDMS melt temperature, and the extent of PDMS crystallinity. The PMMA molecular weight scales with PMMA concentration in the one-step method and is independent of PMMA concentration in the two-step method. At high PMMA concentration, a unique microstructure is also observed in the one-step method wherein the dispersed phase consists of a mixture of PMMA and PDMS nanodomains rather than a continuous PMMA phase. This presentation will focus on characterizing these similar-but-distinct materials, with the ultimate goal of understanding how network structure impacts properties of silicone-organic hybrids.

Synthesis and characterization of two chemically distinct PDMS/PMMA elastomers

ACS Fall 2020 Virtual Meeting

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