Traditionally polydimethylsiloxane (PDMS) elastomers are prepared by chemical crosslinking reactions [1]. As a result, a covalently bonded polymer network is formed, which gives elastomeric properties [2]. However, since the polymer backbones are covalently interconnected, elastomers are relatively difficult to process and recycle [3, 4]. To overcome these drawbacks, different approaches have been applied to form thermoplastic elastomers (TPEs) including self-assemblies through supramolecular interactions [5, 6].However, the non-covalent bonding forces obtained by simple hydrogen bonding (H-bond) result in too weak mechanical properties. Therefore, systems based on stronger physical association, have been prepared from more specific hydrogen bonding species, such as, 2-ureido-4[1H]-pyrimidone (UPy), possessing two H-bond acceptors and donors (Figure 1c). Such quadruple H-bonded units can form dimers, which have been exploited for preparation of tough PDMS TPEs [4]. However, softer PDMS TPEs cannot be prepared by this approach, since they again suffer from too weak associations between chains. Here we show how a combination of UPy and urea as strong and weak H-bond can be combined to prepare the soft PDMS TPE (Figure 1a). The urea bond (figure 1b) acts as a sacrificial bond under deformation whereas UPy plays a role as a strong crosslinker (Figure 1c). Moreover, these two H-bonds can be disassociated at raised temperature (or by organic solvents) (Figure 1d). The obtained polymer melt (or polymer solution) then can be remolded, illustrating the possibility of direct recycling of PDMS elastomers.

Soft thermoplastic silicone elastomer via supramolecular chemistry

ACS Fall 2020 Virtual Meeting

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