A Thermo-Reversible Silicone Elastomer with Remotely Controlled Self-Healing Poster ID: # SM01.03.18  Contact e-mail: al@kt.dtu.dk Danish Polymer Centre Elisa Ogliani, Liyun Yu, Irakli Javakhishvili, Anne Ladegaard Skov* Danish Polymer Centre, Department of Chemical and Biochemical Engineering, DTU, 2800 Kgs. Lyngby, Denmark Abstract Soft thermoplastic elastomers with increased durability are in high demand for a broad spectrum of applications. Silicone elastomers are soft and durable, but they are not thermoplastic in nature and, under extreme conditions, reliability may also suffer. Thus, as a solution to these shortcomings, we report the synthesis of a thermo-reversible, self-healing and recyclable silicone elastomer, namely P(PDMSMA-co-UPyMA)[1]. Stimuli-responsivity is imparted to the silicone copolymer by incorporating supramolecular 2-ureido-4[1H]-pyrimidone (UPy)[2] self-assembling motifs (Figure 1). Self-healing of the novel elastomer may be triggered by both direct and indirect heating[3], the latter by means of incorporating Fe3O4 particles into the elastomer and subsequent exposure to an alternating magnetic field (AMF). 1 Synthesis and characterisation P(PDMSMA-co-UPyMA) was synthesised via free radical polymerisation of monomethacryloxypropyl terminated polydimethylsiloxane (PDMSMA) and 6-methyl-2-ureido-4[1H]-pyrimidone-bearing methacrylate (UPyMA) monomers (Figure 2), resulting in a random distribution of the hydrogen bonding groups along the backbone. The UPyMA molar fraction in the copolymer was quantified to 11% on the basis of 1H NMR analysis. Figure 1. Schematic representation of UPy dimers, characterised by a self-complementary array of four hydrogen bonds. Figure 2. Chemical structure of P(PDMSMA-co-UPyMA). Recyclability Thermo-responsivity: self-healing by direct heating Figure 4. Small-amplitude oscillatory shear rheology: shear storage moduli G´ and shear loss moduli G´´ of pure P(PDMSMA-co-UPyMA) and the magnetic composite measured at 25˚C, 50˚C and 70˚C. Figure 3. Comparison of tensile stress and tensile strain of P(PDMSMA-co-UPyMA) after repeated recycling by solvent casting. Multiple shapes obtained by consecutively reprocessing the material are displayed in the bottom (copolymer filled with iron oxide particles is used as an example). Figure 5. Tensile stress and tensile strain of pure P(PDMSMA-co-UPyMA), before and after healing for 1h in oven at a pre-set temperature of 55 ˚C and 70˚. Remotely controlled self-healing triggered by exposure to an alternating magnetic field (AMF) (a) Figure 6. (a) Pure P(PDMSMA-co-UPyMA) and (b) P(PDMSMA-co-UPyMA) filled with iron oxide particles. (c) Heating temperature profiles of the composite filled with 0, 10, and 20wt% particles and exposed to an AMF at a frequency of 110.1 kHz. Conclusions Shear rheology measurements prove the dynamic nature and the thermo-responsivity of the bonds within the supramolecular network of the copolymer. P(PDMSMA-co-UPyMA) can be reshaped multiple times, without losing its original properties and, therefore, it is proven recyclable. The pure elastomer is capable of healing completely by means of heat supply in relatively mild conditions. The composite filled with 20wt% Fe3O4 exhibits promising self-healing efficiencies, calculated as ηε= 78% (percentage of restored tensile strain, ε) and ησ= 70% (percentage of restored tensile stress, σ). Figure 7. (a) Tensile stress and tensile strain of P(PDMSMA-co-UPyMA) filled with 20wt% Fe3O4 particles, before and after healing for 2h following exposure to an AMF. (b), (c) SEM images of the magnetic composite after AMF triggered self-healing and (d) elemental mapping of the specimen by EDS (iron distribution is visualised as red dots). References [1] E. Ogliani, L. Yu, I. Javakhishvili, A. L. Skov, RSC Adv. 2018, 8, 8285-8291. [2] F. H. Beijer, R. P. Sijbesma, H. Kooijman, A. L. Spek, E. W. Meijer, J. Am. Chem. Soc. 1998, 120, 6761-6769. [3] C. C. Corten, M. W. Urban, Adv. Mater. 2009, 21, 5011-5015.