Although Staudinger realized makromoleküles had enormous potential, he likely did not anticipate the consequences of their universal adoption. With 6.3 billion metric tons of plastic waste now contaminating our land, water, and air, we are facing an environmental and public health crisis. Synthetic polymer chemists can help create a more sustainable future, but are we on the right path to do so? Herein, a comprehensive literature survey reveals that there has been an increased focus on “sustainable polymers” in recent years, but most papers focus on biomass-derived feedstocks. In contrast, there is less focus on polymer end-of-life fates. Moving forward, we suggest an increased emphasis on chemical recycling, which sees value in plastic waste and promotes a closed-loop plastic economy. To help keep us on the path to sustainability, the synthetic polymer community should routinely seek the systems perspective offered by life cycle assessment.

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[2.2]paracyclophane (pCp), unlike many π-building blocks, has been virtually unexplored in supramolecular constructs. Reported here is the synthesis and characterization of the first pCp derivatives capable of programmed self-assembly into extended cofacial π-stacks in solution and the solid state. The design employs transannular (intramolecular) hydrogen bonds (H-bonds), hitherto unstudied in pCps, between pseudo-ortho-positioned amides of a pCp-4,7,12,15-tetracarboxamide (pCpTA) to preorganize the molecules for intermolecular H-bonding with π-stacked neighbors. X-ray crystallography confirms the formation of homochiral, one-dimensional pCpTA stacks helically laced with two H-bond strands. The chiral sense is dictated by the planar chirality (Rp or Sp ) of the pCpTA monomers. A combination of NMR, IR, and UV/Vis studies confirms the formation of the first supramolecular pCp polymers in solution.

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Reported here is the synthesis, characterization, and isodesmic supramolecular polymerization of [3.3]­paracyclophane-5,8,14,17-tetracarboxamide ([3.3]­pCpTA). The self-assembling monomer, a bridge-expanded homolog of [2.2]­paracyclophane-4,7,12,15-tetracarboxamide ([2.2]­pCpTA), forms homochiral assemblies in nonpolar solution and the solid state through double-helical intermolecular and transannular hydrogen bonding. The additional methylene unit in the [3.3]­paracyclophane bridge results in a weakened supramolecular assembly for [3.3]­pCpTA compared to [2.2]­pCpTA in solution. Likely origins of the change in assembly strength, revealed through X-ray crystallography, computational analysis, and solution-phase spectroscopy, are an increase in (a) the intramolecular and intermolecular deck-to-deck spacing compared to [2.2]­paracyclophane resulting from larger amide dihedral angles accompanying transannular hydrogen bonding in the [3.3]­paracyclophane and (b) monomer entropy associated with the scissoring motion of the [3.3]­paracyclophane bridge.