Thymine-Modified Silicones: A Bioinspired Approach to Cross-Linked, Recyclable Silicone Polymers

In DNA, thymine typically forms hydrogen bonds with adenine to hold two complementary strands together and to preserve the genetic code. While thymine is typically absent in RNA, a thymine-thymine hydrogen bonding structure is reminiscent of the wobble region in tRNA recognition, where noncanonical base pairing can occur. This noncanonical base pairing can be applied to synthetic polymer systems, where thymine is free to hydrogen bond with itself. In this work, the natural hydrogen bonding capacity of thymine was used to produce silicone polymer systems designed to be cross-linked by hydrogen bonds. Backbone and end-group-modified silicones were synthesized with differing concentrations of thymine, which facilitated the cross-linking of the polymeric strands. Removing the hydrogen on N3─which is typically involved in hydrogen bonding─resulted in systems with similar viscosities to the starting material and that were devoid of any apparent cross-links. Differential scanning calorimetry (DSC) studies of the thymine-modified polymers displayed thermal absorptions and releases, indicative of bond breaking and reformation, around 100 and 60 °C, respectively. The cycle of bond breaking and formation could be repeated without any noticeable degradation of the chemical structure of the polymers. These polymeric materials could be readily recycled and remolded by heating them at 110 °C for 5 min, followed by cooling to room temperature, confirming their thermoplastic nature.