Norbornyl benzocyclobutene ladder polymers: Conformation and microporosity

Abstract

Shape-persistent contorted ladder polymers are an intriguing and unusual class of polymers. Using catalytic arene-norbornene annulation (CANAL) polymerization and with norbornadiene and dibromoarenes as monomers, we synthesized a series of ladder polymers with fused norbornyl benzocyclobutene backbones and varied conformations. A diaryl spiro-orthocarbonate monomer was used to reorient the ladder backbone perpendicularly to induce three-dimensional kinks, and a p-dibromo-xylene comonomer was used to statistically vary the distance between the spirocyclic kinks in the ladder backbone. Norbornyl benzocyclobutene ladder polymers with no spirocyclic backbone twists possess much more compact conformations than ladder polymers with frequent spirocyclic backbone twists in solution. While spirocyclic twists in the polymer backbone had minor effects on the surface area and microporosity, incorporation of rotatable single bonds in the repeat unit significantly decreased both the surface area and pore volume. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3075–3081.