Acetoacetate based thermosets prepared by dual-Michael addition reactions

A novel set of dual-curable multiacetoacetate-multiacrylate-divinyl sulfone ternary materials with versatile and manipulable properties are presented. In contrast to common dual-curing systems, the first stage polymer herein consists of a densely crosslinked, high Tg network as a result of base-catalyzed multiacetoacetate-divinyl sulfone Michael addition. A more flexible secondary network forms after base-catalyzed Michael addition of remaining multiacetoacetate to multiacrylate. Curing is truly sequential as the rates of the two Michael additions are significantly different. Curing kinetics were analyzed using differential scanning calorimetry (DSC) and Fourier-transform infrared (FTIR). The materials at each curing stage were characterized using dynamic mechanical analysis (DMA) and SEM. Although some phase separation was observed in certain formulations, the incompatibilities were minimized when the molar percentage of the acetoacetate-divinyl sulfone polymer network was above 75%. Furthermore, the environmental scanning electron microscopy (ESEM) images of these materials show that the more flexible acetoacetate-acrylate phase is dispersed in the form of polymeric spheres within the rigid acetoacetate-divinyl sulfone matrix. This unique dual microstructure can potentially render these materials highly resilient in applications requiring densely crosslinked polymer architectures with enhanced toughnesPostprint (published version

Sequential curing of thiol-acetoacetate-acrylate thermosets by latent Michael addition reactions

Thiol-acetoacetate-acrylate ternary dual-curing thermosets were prepared by a sequential process consisting of thiol-Michael addition to acrylates at room temperature followed by Michael addition of acetoacetates to acrylates at moderately elevated temperature. The curing sequence can be controlled with the help of the different acidities of the protons on thiol and acetoacetate groups, the favorable pKa of the base used as catalyst and the self-limiting character of Michael additions. The latency of the curing steps can be regulated by selection of the right catalysts, temperature and curing conditions. The properties of the intermediate and final materials can be tuned by changing the structure of the monomers and the contribution of both Michael addition reactions.Postprint (author's final draft

Synthesis of novel β-aminocyclobutanecarboxylic acid derivatives by a solvent-free aza-Michael addition and subsequent ring closure

Novel beta-aminocyclobutanecarboxylic acid derivatives were prepared via a sequential solvent-free aza-Michael addition of benzophenone imine across 3-halopropylidenemalonates and base-induced ring closure. These highly substituted cyclobutanedicarboxylic acid derivatives were subjected to a reactivity study which demonstrated the tendency of these donor-acceptor substituted four-membered rings to be converted into their corresponding ring-opened products

Stability conditions and Kleinian singularities

We describe the spaces of stability conditions on certain triangulated categories associated to Dynkin diagrams. These categories can be defined either algebraically via module categories of preprojective algebras, or geometrically via coherent sheaves on resolutions of Kleinian singularities. The resulting spaces are related to regular subsets of the corresponding complexified Cartan algebras.Comment: This version fills a gap in the proof of the main results pointed out by Michael Wemyss. The only changes are footnotes on pages 3,5 and the addition of Remark 3.

Stereochemical Studies on a New Ciramadol Analogue by NMR-Spectroscopy

The absol. configuration of a Ciramadol analogue obtained from (-)-menthone is established by 'H-NMR-. simulated NMR-, COSY-90-, and NOEmeasurements. The final compound 2-(a-1 -pyrrolidino)benzy 1-4-isopropyl- 1 -methyl-cyclohexan-3-one (4b), e.g.. has 1R.2S,4S.l IS-configuration due to stereoselective Michael-type addition of pyrrolidine to the pertinent benzylidene intermediate 3. Die absol. Konfiguration einer Ciramadol-analogen Verbindung aus (-)- Menthon wurde durch 'H-NMR-. simulierte NMR-. COSY-90- und NOEUntersuchungen geklärt. Danach hat die als Beispiel untersuchte Verbindung 2-(a-1 -Pyrrolidino)benzyl-4-isopropyl-1 -methyl-cyclohexan-3-on (4b) 1R,2S.4S.l IS-Konfiguration, die durch eine stereoselektive Michael-analoge Addition des Pyrrolidins an die entspr. Benzyliden-Verbindung 3 entsteht

Explanation = Unification? A New Criticism of Friedman’s Theory and a Reply to an Old One

According to Michael Friedman’s theory of explanation, a law X explains laws Y1, Y2, …, Yn precisely when X unifies the Y’s, where unification is understood in terms of reducing the number of independently acceptable laws. Philip Kitcher criticized Friedman’s theory but did not analyze the concept of independent acceptability. Here we show that Kitcher’s objection can be met by modifying an element in Friedman’s account. In addition, we argue that there are serious objections to the use that Friedman makes of the concept of independent acceptability

Sequential curing of amine-acrylate-methacrylate mixtures based on selective aza-Michael addition followed by radical photopolymerization

Dual curing systems find various uses in industry with the process flexibility they provide which allows tailoring properties at different curing stages in accordance with application requirements. A safe and efficient dual curing scheme is proposed here for a set of mixtures containing different proportions of acrylates and methacrylates. The first curing stage is a stoichiometric aza-Michael addition between acrylates and an amine, followed by photo-initiated radical homopolymerization of methacrylates and remaining acrylates. An analysis of aza-Michael reaction kinetics confirmed that amines react selectively with acrylates, leaving methacrylates unreacted after the first curing stage. It was found that acrylate-rich mixtures achieve complete global conversion at the end of the scheme. However, the highest crosslinking density and thermal resistance was observed in a methacrylate-rich formulation. The resulting materials show a wide range of viscoelastic properties at both curing stages that can be tailored to a variety of industrial application needs.Postprint (author's final draft

Superelastic and pH-Responsive Degradable Dendrimer Cryogels Prepared by Cryo-aza-Michael Addition Reaction

Dendrimers exhibit super atomistic features by virtue of their well-defined discrete quantized nanoscale structures. Here, we show that hyperbranched amine-terminated polyamidoamine (PAMAM) dendrimer G4.0 reacts with linear polyethylene glycol (PEG) diacrylate (575 g/mol) via the aza-Michael addition reaction at a subzero temperature (−20 °C), namely cryo-aza-Michael addition, to form a macroporous superelastic network, i.e., dendrimer cryogel. Dendrimer cryogels exhibit biologically relevant Young’s modulus, high compression elasticity and super resilience at ambient temperature. Furthermore, the dendrimer cryogels exhibit excellent rebound performance and do not show significant stress relaxation under cyclic deformation over a wide temperature range (−80 to 100 °C). The obtained dendrimer cryogels are stable at acidic pH but degrade quickly at physiological pH through self-triggered degradation. Taken together, dendrimer cryogels represent a new class of scaffolds with properties suitable for biomedical applications