Model Transient Networks from Strongly Hydrogen-Bonded Polymers

Random copolymers consisting of n-butyl acrylate backbones with quadruple hydrogenbonding side chains based on 2-ureido-4[1H]-pyrimidinone (UPy) have been synthesized via controlled radical polymerization and postpolymerization functionalization. Through this synthetic strategy highUPymonomer content (15 mol %) can be reached while maintaining low polydispersity and excellent control over molecular weight, providing model reversible networks with well-defined molecular architecture. Despite low Tgs and a lack of entanglements or crystallinity, these materials behave as thermoplastic elastomers through the strong but reversible association of UPy groups. Bulk properties such as the plateau modulus, tensile modulus, and relaxation time scale are primarily determined by the average distance betweenUPy’s along the chain. Starting froma difunctional initiator, triblock copolymers can also be synthesized containing a homopolymermidblock and randomcopolymer end blocks, effectively concentrating the hydrogen-bonding groups near the chain ends. By controlling both the average composition and distribution of UPy’s along the polymer chain, macroscopic material properties such as stiffness and resistance to creep can be independently tuned.