Crosslinked internal alkyne-based stereo elastomers: polymers with tunable mechanical properties

New methods to introduce and control polymer network crosslinking and improve mechanical properties of the resulting materials have been investigated extensively. Common methods to enhance the mechanical properties of elastomers include “vulcanization” by which polymer chains are covalently crosslinked. In this work, we outline a new method to crosslink well-defined, synthetic elastomers using “click” reactions. Specifically, 2-butyne-1,4-diyl dipropiolate which possesses both external and internal alkynes, was synthesized as a functional monomer and copolymerized with dithiols to yield a series of elastomeric materials possessing variations in cis stereochemistry. Notably, the glass-transition temperature and mechanical properties of the resulting copolymers can be tuned by changing the stoichiometry between 2-butyne-1,4-diyl dipropiolate and 1,3-propane diyl dipropiolate. The alkyne functionalities within the backbone allow for post-polymerization interchain crosslinking to form polymer networks using a ruthenium-catalyzed azide–alkyne cycloaddition. Hysteresis tests have shown that tensile modulus and recovery can be controlled by the density of the crosslinking within the network.