Metal-Free Polymerizations of Microencapsulated Activated Alkynes for Autonomous Damage Visualization of Polymers

The development of autonomous materials with desired performance and built-in visualizable sensing units is of great academic and industrial significance. Although a wide range of damage indication methods have been reported, the “turn-on” sensing mechanism by damaging events based on microcapsule systems, especially those relying on chemical reactions to elicit a chromogenic response, are still very limited. Herein, a facile and metal-free polymerization route with an interesting reaction-induced coloration effect is demonstrated. Under the catalysis of 1,4-diazabicyclo[2.2.2]octane (DABCO), the polymerizations of difunctional or trifunctional activated alkynes proceed very quickly at 0 oC in air. A series of polymers composed of stereoregular enyne structure (major unit) and divinyl ether structure (minor unit) are obtained. Both the catalyst and monomers are colorless while the polymerized products are deep-colored. This process can be applied for the damage visualization of polymers using the microencapsulation technique. Microcapsules containing the reactive alkyne monomer are prepared and mixed in a DABCO-dispersed polymer film. The mechanical damage of this composite film can be readily visualized once the reaction is initiated from the ruptured microcapsules. Moreover, the newly formed polymer automatically sealed the cracks with an additional protection function.

Synthesis and Toxicity Evaluation of New Pyrroles Obtained by the Reaction of Activated Alkynes with 1-Methyl-3-(cyanomethyl)benzimidazolium Bromide

A series of new pyrrole derivatives were designed as chemical analogs of the 1,4-dihydropyridines drugs in order to develop future new calcium channel blockers. The new tri- and tetra-substituted N-arylpyrroles were synthesized by the one-pot reaction of 1-methyl-3-cyanomethyl benzimidazolium bromide with substituted alkynes having at least one electron-withdrawing substituent, in 1,2-epoxybutane, acting both as the solvent and reagent to generate the corresponding benzimidazolium N3-ylide. The structural characterization of the new substituted pyrroles was based on IR, NMR spectroscopy as well as on single crystal X-ray analysis. The toxicity of the new compounds was assessed on the plant cell using Triticum aestivum L. species and on the animal cell using Artemia franciscana Kellogg and Daphnia magna Straus crustaceans. The compounds showed minimal phytotoxicity on Triticum rootlets and virtually no acute toxicity on Artemia nauplii, while on Daphnia magna, it induced moderate to high toxicity, similar to nifedipine. Our research indicates that the newly synthetized pyrrole derivatives are promising molecules with biological activity and low acute toxicity.

Multicomponent Cyclopolymerization of Alkynes, Isocyanides and Isocyanates Toward Heterocyclic Polymers

<p>Multicomponent cyclopolymerization (MCCP) based on isocyanides, among the tremendous synthetic methodologies, is a powerful tool for the preparation of functional heterocyclic polymers like poly(maleimide)s (PMDs), which should be further developed. In this work, an atom-economic and catalyst-free MCCP of activated alkynes, diisocyanides and diisocyanates was fully explored. The PMDs with high weight-average molecular weights (<i>M</i>_w up to 29 000) were facilely produced in satisfactory yields (up to 85%). The resultant polymers showed excellent solubility, high thermal stability, and good film-forming ability, and their thin films possessed high refraction indices (RI) in a range of 1.613 to 1.708 at 632.8 nm. Therefore, this work not only supplements the isocyanide-based multicomponent cyclopolymerizations but also enriches the family of polymerization reactions based on triple-bond building blocks. </p>

Multicomponent Cyclopolymerization of Alkynes, Isocyanides and Isocyanates Toward Heterocyclic Polymers

<p>Multicomponent cyclopolymerization (MCCP) based on isocyanides, among the tremendous synthetic methodologies, is a powerful tool for the preparation of functional heterocyclic polymers like poly(maleimide)s (PMDs), which should be further developed. In this work, an atom-economic and catalyst-free MCCP of activated alkynes, diisocyanides and diisocyanates was fully explored. The PMDs with high weight-average molecular weights (<i>M</i>_w up to 29 000) were facilely produced in satisfactory yields (up to 85%). The resultant polymers showed excellent solubility, high thermal stability, and good film-forming ability, and their thin films possessed high refraction indices (RI) in a range of 1.613 to 1.708 at 632.8 nm. Therefore, this work not only supplements the isocyanide-based multicomponent cyclopolymerizations but also enriches the family of polymerization reactions based on triple-bond building blocks. </p>

Unexpected ring opening of pyrazolines with activated alkynes: Synthesis of 1H-pyrazole-4,5-dicarboxylates and chromenopyrazolecarboxylates

1H-Pyrazole-4,5-dicarboxylates and chromenopyrazole carboxylates were prepared by reacting pyrazolines with activated alkynes under neat conditions without catalyst. The products were formed via unexpected ring opening of pyrazolines with the elimination...