Macromolecules, Vol.53, No.20, 9086-9096, 2020
Crystallizable Supramolecular Polymers: Binding Motif and Processing Matter
A systematic investigation of the influence of the binding motif and the processing history on the formation, crystallization, and mechanical properties of supramolecular polymers (SMPs) with a crystallizable core is reported. Telechelic, low-molecular-weight poly(butylene adipate) (PBA, 2700 g mol(-1)) was end-functionalized with either quadruple hydrogen-bonding 2-ureido-4[1H]pyrimidinone (UPy) motifs or 2,6-bis(1 '-methylbenzimidazolyl)pyridine (Mebip) ligands. The UPy-based macromonomer spontaneously self-assembles into an SMP, whereas the Mebip-terminated building block was chain-extended by complex formation with a stoichiometric amount of Zn(NTf2)(2). We show that the morphology and the properties of the SMPs are strongly affected by the nature of the supramolecular binding motif and also the processing parameters. In the case of the UPy-functionalized SMP, all processing conditions led to microphase segregation of the supramolecular binding motifs and the PBA cores. When this material was solution-cast or compression-molded, the crystallization of dimerized UPy stacks occurred first and stifled the PBA crystallization. This afforded flexible materials with storage moduli E ' of 72-92 MPa and a tensile strength (sigma(max)) of 3.6 MPa (all at 25 degrees C). When UPy-functionalized PBA was rapidly quenched from the melt, both microphases crystallized readily, and this led to much stiffer materials, with E ' = 673 MPa and sigma(max) = 5 MPa. No phase segregation was observed for the metallosupramolecular polymer. In this case, all processes investigated afforded materials with a crystalline PBA phase, but crystallization from the melt was, at least at ambient temperature, very slow. This material displays an E ' of 645-913 MPa and a sigma(max) of 6.0-7.6 MPa, which represents a significant improvement over a low-molecular-weight PBA reference.