Imide-yne click polymerization: A new and versatile tool for the toolbox of X-yne click polymerization

Abstract

The Michael reaction, also known as 1,4-conjugate addition, is a cornerstone in both organic and polymer chemistry, have influence upon the field through its versatility in forming carbon-carbon and carbon-heteroatom bonds leads the way for groundbreaking advancements in complex molecule and macromolecule construction. Click chemistry comprises a collection of modular, minimum by-product, stereospecific, and atom-economical, reactions that proceed under mild conditions with easily accessible monomers. Michael additions of heteronucleophiles to activated alkynes are faster and proceed under milder conditions than traditional Michael addition reactions. Thus, Michael reactions of activated alkynes meet the conditions that outlined by click chemistry. On the scale of macromolecular/polymeric entities, these reactions generally referred as 'X-yne click polymerization' in which "X" stands for a heteronucleophile such as thiol, amino, hydroxyl or phosphite. Poly(imide)s are appealing polymers to produce high-performance materials with many outstanding features, including high solvent resistance, superior mechanical properties, thermooxidative and thermal stability. These properties make poly(imide)s suitable for use in industrial fields such as aerospace, automotive, electronics, pharmacology and agriculture. To the best of our knowledge, there is a lack of research on the synthesis of poly(imide)s via X-yne click polymerization method. In this study, linear poly(imide ester)s were synthesized with bisimides and dipropiolates through imide-yne click reaction in the presence of a mild base 1,4-diazabicyclo[2.2.2] octane (DABCO) at room temperature, proceeding in an anti-Markovnikov fashion and yielding the E-isomer as the major product. Bisimide compounds were obtained through two different synthetic routes: heating commercially available dianhydrides with urea or Michael reaction between maleimide and different thiols or piperazine. Dipropiolates were achieved via an esterification reaction between various diols and propiolic acid. Following the click polymerization, we further modified the reactive vinyl groups on the main chain with 1-propanethiol, using a stronger base 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as the catalyst. Utilizing the mono-addition nature of the imide-yne click reaction, imide-yne monomers were also developed, and poly(imide thioether)s were synthesized through thiol-ene reaction with 1,6-hexanedithiol (HDT) using TBD as catalyst in 5 minutes at room temperature. Collectively, in this study, with imide-yne reaction we demonstrated a facile strategy for polyimide synthesis in a time- and energy-saving approach. We believe that imide-yne with thiol-ene reactions can also be a useful tool for organic chemists in the synthesis of optically active compounds which can have potential applications in agriculture and medicine as intermediates.