Photoinitiation of polymerizations predicated on the copper(we)-catalyzed azide-alkyne cycloaddition (CuAAC) response

Photoinitiation of polymerizations predicated on the copper(we)-catalyzed azide-alkyne cycloaddition (CuAAC) response enables spatio-temporal control and the forming of mechanically robust highly glassy photopolymers. part reactions in four specific phases: initiation reduced amount of copper cycloaddition and termination. Initiation in the cleavage is involved by this case of photo-responsive substances to create radicals upon UV or visible light irradiation. Subsequently the reduced amount of the copper(ii) varieties into catalytically energetic copper(we) happens45 parallel to additional competing reactions such as for example re-oxidation of copper(we) to copper(ii) further reduced amount of copper(i) to copper(0) and disproportionation of copper(i) to copper(ii) and copper(0).23 The cycloaddition stage itself is a complex multi-step mechanism involving copper diffusion σ- and π-coordination with alkynes six-membered band formation between copper-acetylides and azides and the best release of copper.50 Termination occurs Dynasore when copper(i) loses its catalytic activity by oxidation or disproportionation. Previously additional mechanistic studies coping with either experimental or computational modeling verified that the CuAAC reaction rate had a second order dependence on copper concentration 50 the formation of six-member rings during cycloaddition was a rate determining step 51 and other plausible side reactions such as alkyne coupling hindered the reaction rate by forming inactive species23 52 though all of these conclusions depend at least somewhat on the reaction conditions used. Scheme 1 Proposed reaction diagram of one approach to photo-initiated Dynasore CuAAC-based polymerizations: (a) photoinitiation copper reduction to form Cu(i) and cycloaddition between azides and alkynes. (b) Side reactions that can Mouse Monoclonal to E2 tag. potentially occur during the course … The nature of step-growth polymerizations enables the CuAAC polymerization to form relatively homogeneous polymer networks 53 where the rigid-aromatic triazole adducts formed throughout the network as a product of the CuAAC reactions exhibit excellent thermal and chemical stability while Dynasore also increasing the polymer stiffness and glass transition temperature.1 48 However the azide moieties can be explosive when sufficiently concentrated; therefore designing higher molecular weight azide monomers is essential to enable bulk polymerizations to be performed safely and efficiently.54 In addition the solubility of copper in organic substrates is often insufficient either requiring an addition of chelating ligands to increase solubility or only allowing for minimal concentrations of copper to be incorporated into the resin mixtures.31 Due to the aforementioned challenges previous investigations of the CuAAC polymerization kinetics in bulk are limited. Herein we explore the effects of monomer structure copper and photoinitiator concentrations light exposure conditions temperature solvent light intensity and irradiation times on the rate of bulk CuAAC polymerization to understand this complex polymerization and enable the determination of optimal polymerization conditions for spatially and temporally controlled formation of photopolymerized CuAAC thermosets. Experimental section Materials 1 3 4 4 isocyanate) 1 3 4 4 isocyanate) bis(4-hydroxyphenyl)-methane 6 dibutyltin dilaurate sodium azide 1 1 1 pentaerythritol 1 3 5 phloroglucinol propargyl alcohol sodium Dynasore hydride diethyl azodicarboxylate tetrabutylammonium iodide -pentamethyldiethyl-enetriamine (PMDETA) copper(ii) chloride Dynasore triphenyl-phosphine 2 2 (DMPA) propargyl bromide camphorquinone (CQ) tetrahydrofuran and acetonitrile were used as received from Sigma Aldrich. 2 2 4 4 3 5 hexyl isocyanate 6 1 2 Dynasore (PPD) 2 2 3 sodium hydroxide potassium carbonate potassium hydroxide hydrochloric acid methanol acetone methylene chloride and dimethylformamide were used as received from Fisher Scientific. Diphenyl(2 4 6 oxide (Lucirin-TPO) was used as received from VWR International. Bis(2 4 6 (I819) was used as received from BASF. All azides were synthesized according to the azide safety rules and handled with appropriate care and precaution and generally working with the monomers resins and polymers in small quantities.54 Three facile reaction schemes.