No abstract

Polymers that depolymerize back to monomers can be repeatedly chemically recycled, thereby reducing their environmental impact. Polyphthalaldehyde is a metastable polymer that is rapidly and quantitatively depolymerized due to its low ceiling temperature. However, the effect of substitution on the physical and chemical properties of polyphthalaldehyde derivatives has not been systematically studied. Herein, we investigate the cationic polymerization of seven o-phthalaldehyde derivatives and demonstrate that judicious choice of substituents results in materials with a wide range of ceiling temperatures (<-60 to 106 °C) and decomposition temperatures (109-196 °C). We anticipate that these new polymers and their derivatives will enable researchers to access degradable materials with tunable thermal, physical, and chemical properties.

Poly(p-phenylene vinylene)s (PPVs) and poly(arylene vinylene)s are key materials for a variety of applications ranging from organic light emitting diodes to fluorescent optical probes. Their syntheses, however, have been hampered by non-living or step-growth polymerization techniques. The development of functional-group tolerant olefin metathesis catalysts has enabled the use of living ring-opening metathesis polymerization (ROMP) of cyclophane monomers yielding PPVs and poly(p-phenylene-co-arylene vinylene)s in a living manner. Low dispersity and soluble PPVs are afforded with control over the number of repeat units with easy incorporation of different end-groups at their heads or tails. In this review, a comprehensive overview of tetrasubstituted and disubstituted alkyl and alkoxy containing [2.2]paracyclophane-1,9-diene, [2.2]metaparacyclophane-1,9-diene, [2.2.2]paracyclophane-1,9,17-triene, and benzothiadiazole-[2.2]paracyclophane-1,9-diene is provided. The high ring strain of these monomers enables efficient polymerizations with ruthenium initiators. A particular emphasis is on [2.2]paracyclophane-1,9-dienes as it is the most investigated class of polymerized cyclophanediene since initially reported 30 years ago. Additionally, applications for soft materials synthesized by ROMP are examined, highlighting easily accessed PPV copolymers and PPV block copolymers that can be phototriggered, as well as PPVs featuring supramolecular recognition units installed at their termini to afford orthogonally self-assembled architectures.

<div><p>Polymers that depolymerize back to monomers can be repeatedly chemically recycled, thereby reducing their environmental impact. Polyphthalaldehyde is a metastable polymer that is rapidly and quantitatively depolymerized due to its low ceiling temperature. However, the effect of substitution on the physical and chemical properties of polyphthalaldehyde derivatives has not been systematically studied. In this work, we investigate the cationic polymerization of seven distinct <i>o</i>‑phthalaldehyde derivatives and demonstrate that judicious choice of substituents results in materials with a wide range of ceiling temperatures (from < –60 to 106 °C) and decomposition temperatures (109–196 °C). We anticipate that these new polymers and their derivatives will enable researchers to access degradable materials with tunable thermal, physical, and chemical properties.</p></div>

Identifying intermediates of Ni-containing reactions can be challenging due to the high reactivity of Ni complexes and their sensitivity toward air and moisture. Many Ni bidentate phosphine complexes are diamagnetic and can be analyzed in situ via 31P NMR spectroscopy, but the oxidation state of Ni is difficult to determine using 31P chemical shift analysis alone. The J-coupling between P atoms, J PP, has been proposed to correlate with oxidation state, but few investigations have looked at how J PP is affected by parameters such as length of the linker or identity of the phosphine or other ligands. The present investigation into the J PP values of Ni bidentate phosphine complexes with two-carbon and three-carbon linkers shows that the J PP values observed in 31P NMR spectra, |J PP|, are competent indicators of the oxidation state at Ni. For complexes with two-carbon linkers, |J PP| > 40 Hz is typical of Ni0 while |J PP| < 30 Hz is typical of NiII; this trend is reversed for complexes with three-carbon linkers. Additionally, the Lewis acidity of the Ni and Lewis basicity of the phosphine ligand affect J PP predictably. For example, increased P-to-Ni donation arising from more-donating phosphines or more-withdrawing ligands trans to the P atoms causes a more negative J PP. These results should enable the oxidation state of Ni and properties of ligands in Ni bidentate phosphine complexes to be determined in situ during reactions containing these species.