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Polymer networks containing transient physical and permanent chemical cross-links exhibit unique mechanical properties due to the intrinsic reassociating ability of supramolecular functional groups. Similar to supramolecular gels, these networks allow the controlled release of stored energy and can extend the life of polymer networks in practical applications. In this study, we investigated the rheology, dielectric spectroscopy, stress–strain behavior, and dynamic mechanical analysis of networks based on long polybutylene oxide (PBO) chains functionalized with randomly placed thymine (Thy) side groups. A transient network was formed by proportionally mixing this matrix with short non-entangled linear 1,3,5-diaminotriazine (DAT) head–tail modified PBO chains, exploiting the hetero-complementarity of the DAT–Thy triple hydrogen bond. This transient polymer network was further cross-linked to a dual network via a thiol-ene click reaction to form static covalent bonds. In PBO, the similar polarity of the PBO matrix and the DAT–Thy functional groups ensures that the molecular chain motion is not affected by segregation, resulting in a homogeneous polymer phase without microphase-separated functional group domains. Dielectric relaxation spectroscopy was combined with rheology to quantify the relaxation processes of the interconnected polymers and the strength of the DAT–Thy bonding interactions in the melt. The results showed two distinct plateaux in the relaxation modulus due to contributions from hydrogen and permanent bonds. In the case of the dual network, the lifetime of the hydrogen bond was prolonged and higher activation energy was observed due to the physical cross-link preventing the movement of the long chain.

Living animal cells are strongly influenced by the mechanical properties of their environment. To model physiological conditions ultrasoft cell culture substrates, in some instances with elasticity (Young's modulus) of only 1 kPa, are mandatory. Due to their long shelf life PDMS-based elastomers are a popular choice. However, uncertainty about additives in commercial formulations and difficulties to reach very soft materials limit their use. Here, we produced silicone elastomers from few, chemically defined and commercially available substances. Elastomers exhibited elasticities in the range from 1 kPa to 55 kPa. In detail, a high molecular weight (155 kg/mol), vinyl-terminated linear silicone was crosslinked with a multifunctional (f = 51) crosslinker (a copolymer of dimethyl siloxane and hydrosilane) by a platinum catalyst. The following different strategies towards ultrasoft materials were explored: sparse crosslinking, swelling with inert silicone polymers, and, finally, deliberate introduction of dangling ends into the network (inhibition). Rheological experiments with very low frequencies led to precise viscoelastic characterizations. All strategies enabled tuning of stiffness with the lowest stiffness of ~1 kPa reached by inhibition. This system was also most practical to use. Biocompatibility of materials was tested using primary cortical neurons from rats. Even after several days of cultivation no adverse effects were found.