Cyclobutane-1,3-Diacid (CBDA): A Semi-Rigid Building Block Prepared by [2+2] Photocyclization for Polymeric Materials

Abstract

A previously overlooked building block, cyclobutane-1,3-diacid (CBDA), is introduced to materials synthesis due to its great potentials. As an example of CBDA, α-truxillic acid or 2,4-diphenylcyclobutane-1,3-dicarboxylic acid, was readily synthesized from commercially available trans-cinnamic acid. This CBDA showed outstanding stability both in sunlight and upon heating. While its two carboxylic acid groups can be readily utilized in connecting with other molecules to form new materials, the cyclobutane ring was able to tolerate acid and base treatments showing good chemical stability. A series of cyclobutane-containing polymers (CBPs), namely poly-α-truxillates, were obtained by condensation between α-truxillic acid and diols including ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-petanediol, and 1,6-hexanediol. The structures of these poly-α-truxillates were analyzed by NMR, FT-IR, and HRMS. Powder X-ray diffraction results of the poly-α-truxillates indicated that they are semi-crystalline materials. Preliminary thermal, chemical, and photochemical tests showed that the poly-α-truxillates exhibited comparable stabilities to PET.

A Review on the Potential and Limitations of Recyclable Thermosets for Structural Applications

“…[142][143][144] Alternatively, dissociative disulfides can be reversible under UV, 122 shear, and/or heat triggers. 145,146 Alternatively to the thermally induced [4 þ 2] cycloaddition in DA reactions, photoinduced [2 þ 2] and [4 þ 4] cycloadditions are used for the synthesis of linear polymers 147 and reversible cross-linked networks. 148 The main advantage of photo-induced cycloaddition, compared to DA, can be found in the high rate of dimerization.…”

Synthesis of esters of diaminotruxillic bis-amino acids by Pd-mediated photocycloaddition of analogs of the Kaede protein chromophore

“…Moreover, alternative mechanisms to explain the antinociception of truxillic compounds have also been reported [11,12] and have generated intense debate. In addition, truxillic derivatives have shown remarkable activity as hepato-protective agents [13] and they also have applications as internal donors in Ziegler-Natta catalysts for polymerization [14] or as building blocks in polymer chemistry [15].…”

Preparation of the flexible soybean oil‐based material via [2 + 2] cycloaddition photo‐polymerization

“…Trans‐cinnamic acid (CA) is plant derived and can undergo [2 + 2] cycloaddition reaction after UV irradiation at 365 nm. Not only it can form dicarboxylic acid monomer through [2 + 2] cycloaddition reaction first and then be applied for polyester synthesis (thermoplastic material), 17,18 but also it can be connected to the polymer side chain first and then through [2 + 2] cycloaddition reaction to form cross‐linked network structure (thermosetting material) 19,20 . Chung et al achieved crack healing in polymeric materials by photochemical [2 + 2] cycloaddition reaction of a cinnamate monomer, and the photochemical healing process was very fast without any catalyst or severe heat treatment 21 .…”