retro-DA Reaction Research Articles

Patterned Fluorescence Images Based on a Retro Diels-Alder Reaction

are also shown in Figure S2.It is still unclear how the retro DA reaction occurs during the photoirradiation process. We also carried out the patterning process without employing PAG and obtained patterned images with poorer resolution and lower intensity of the fluorescence emission compared with those prepared in the presence of PAG (data not shown). Although it is hard to understand the detailed mechanism including the role of PAG involved with the photo-induced retro DA reaction, we nevertheless, believe that the strong UV light generated from the UV illuminator causes local heating and promote the retro DA reaction in the exposed area (possibly in the presence of the acid generated from PAG).In summary, we have developed a new strategy for the ge-neration of patterned fluorescence images in polymer film. Fluorescent molecules were produced in the UV exposed area. Although high quality image patterns were obtained by un-expected retro Diels-Alder reaction, it would be very intriguing if patterned images could be fabricated by photochemically generated acid-promoted dehydration of Diels-Alder adducts.

ChemInform Abstract: The Pagodane Route to Dodecahedranes. Unsaturated Dodecahedranes, Protection, and Deprotection.

Abstract Monounsaturated, highly pyramidalized, highly reactive (i.a. dienophilic, dipolarophilic) dodecahedranes ( 2,10 ) are prepared from an adequately functionalized bisseco substrate. Cheletropic (-N 2 O; -SO 2 ) and retro-DA reactions are probed as potential methodologies in the preparation of dodecahedrapolyenes.

Thermally reversible crosslinked polyethylene using Diels–Alder reaction in molten state

Thermally reversible crosslinked polyethylene was prepared by Diels–Alder (DA) and retro Diels–Alder (rDA) reaction. Maleimide/furan adduct was used as crosslinking agent. Dienophile named 11-maleimido-undecanoic acid was first synthesized and between this dienophile and commercial 3-(2-furyl) propanoic acid, the DA reaction was studied to determine DA and rDA reactions temperatures in the solid state. Then, an original modification method was employed to graft the two molecules onto the Lotader® poly(ethylene-co-glycidyl methacrylate) in one step procedure. The DA and rDA reactions between diene and dienophile grafted moieties are followed by FT-IR analysis on a thin film. Readily polymer network is synthesized and the cycle of DA and retro-DA reactions is repeatable with no significant polymer degradation.

Optimization of thermal remendability of epoxy via blending

To prepare epoxy materials with improved thermal remendability, two types of epoxy resins ( N, N-diglycidyl-furfurylamine (DGFA) and furfuryl glycidyl ether (FGE)), which were synthesized in the authors' lab and contained different proportions of furan and epoxide groups, were blended and cured by anhydride and maleimide. Like the cured version of either DGFA or FGE alone, the cured blends of DGFA and FGE have also acquired thermal reversibility due to the Diels–Alder (DA) bonds from the reaction between furan and maleimide groups. The addition of FGE into the blends increased the DA bonds density as a result of the higher furan concentration in FGE. Accordingly, remendability originating from successive retro-DA and DA reactions was obviously improved. On the other hand, the crosslinked epoxy networks generated by the reaction between epoxide and anhydride groups were strong enough to provide the blends with acceptable mechanical performance.

Characterisation of N-vinyl-2-pyrrolidone-based hydrogels prepared by a Diels–Alder click reaction in water

N-vinyl-2-pyrrolidone-based hydrogels were prepared by the Diels–Alder reaction in water for the first time. Copolymers of N-vinyl-2-pyrrolidone(VP) and furfuryl methacrylate(FM) were synthesised by free radical polymerisation in toluene at 70 °C by using 2,2′-azobisisobutyronltrile as an initiator. Polymeric dienophile (PEG–AMI) was prepared from N-alaninyl maleimide (AMI) and poly(ethylene glycol) (PEG) by using N, N′-dicyclohexylcarbodiimide (DCC) as a dehydrating agent. The prepared dienes and dienophile were then dissolved in water and mixed, leading to gelation via Diels–Alder reaction after some time. The gelation times of different copolymers and PEG–AMI in different solvents and at different temperatures were measured by the vial inversion method, and the swelling behaviour of dried hydrogels was studied using a general gravimetric method. The gelation time was shorter in water than in organic solvents, and the gelation time decreased with the increase of temperature and FM content in copolymers. Conversely, the swelling ratios increased with the decrease of temperature and FM content in the copolymers. Disassembly experiments suggested that N, N-dimethylformamide (DMF) could accelerate the retro-DA reaction.

“Click Chemistry” in Tailor-Made Polymethacrylates Bearing Reactive Furfuryl Functionality: A New Class of Self-Healing Polymeric Material

This investigation reports the effective use of the Diels-Alder (DA) reaction, a "click reaction" in the preparation of thermally amendable and self-healing polymeric materials having reactive furfuryl functionality. In this case, the DA and retro-DA (rDA) reactions were carried out between the tailor-made homo- and copolymer of furfuryl methacrylate prepared by atom-transfer radical polymerization and a bismaleimide (BM). The kinetic studies of DA and rDA reactions were carried out using Fourier transform infrared spectroscopy. The DA polymers were insoluble in toluene at room temperature. When the DA polymers were heated at 100 degrees C in toluene, it was soluble. This is because of the cleavage between furfuryl functionality and BM. The chemical cross-link density was determined by the Flory-Rehner equation. The cross-linked polymer showed much greater adhesive strength at room temperature, but the adhesive strength was quite low at higher temperature. The self-healing capability was studied by using scanning electron microscopy analysis. The thermal and dynamic mechanical properties of the thermally amendable cross-linked materials were investigated by thermogravimetric analysis and dynamic mechanical analysis.

A thermally remendable epoxy resin

To provide epoxy resin with crack healing capability, an epoxy containing both furan and epoxide groups, N,N-diglycidyl-furfurylamine (DGFA), was synthesized through a two-step approach. When it reacted with N,N′-(4,4′-diphenylmethane) bismaleimide (DPMBMI) and methylhexahydrophthalic anhydride (MHHPA), respectively, a crosslinked polymer with two types of intermonomer linkage was yielded. That is, thermally reversible Diels–Alder (DA) bonds from the reaction between furan and maleimide groups, and thermally stable bonds from the reaction between epoxide and anhydride groups. In this way, cured DGFA possessed not only similar mechanical properties as commercial epoxy, but also thermal remendability that enabled elimination of cracks. The latter function took effect as a result of successive retro-DA and DA reactions, which led to crack healing in a controlled manner through chain reconnection.

Reversible releasing of arms from star morphology polymers

Reversible thermally induced arm release from a star polymer morphology was prepared which consists of furanic functional core and maleimide functional arm which are attached or detached via Diels–Alder (DA) reversible reactions. This approach allows the reversible bonding and debonding at 35–40°C (DA) and 90–100°C (retro-DA). The covalent reversibility of this process consists of 7 cycles of the DA and retro-DA reactions.

Synthesis of Readily Recyclable Biobased Plastics by Diels‐Alder Reaction

Readily recyclable biobased plastics were designed and synthesized utilizing the thermally reversible DA reaction. Furyl-telechelic poly(butylene succinate) prepolymers (PBSF(2)) were extended with bis- and tris-maleimide linkers (M(2) and M(3)) by the DA reaction in the bulk state to produce linear and network polymers, respectively. The DA reaction was able to proceed at 25-80 degrees C, at which crystalline domains of PBSF(2) were present. In the linear polymer system, the molecular weight in the reaction equilibrium was dependent on the chain length of the prepolymer, but almost independent of the reaction temperature. The cycle of DA and retro-DA reactions was repeatable with no prepolymer deterioration.

Thermally reversible cross-linked polyamides and thermo-responsive gels by means of Diels–Alder reaction

Cross-linked polyamides and polyamide gels were prepared from maleimide-containing polyamides and a tri-functional furan compound and showed thermal reversibility in cross-linking behavior and in gel formation through Diels–Alder (DA) and retro-DA reactions. The rate constant k of the DA cross-linking reaction were 1.25–4.83×10 −5 dm 3 mol −1 s −1 in the temperature range of 20–60 °C with an activation energy of 32.1 kJ mol −1. The cross-linking densities, thermal properties, and thermal reversibility of the polyamides/furan polymers were adjustable with the contents of maleimide groups in polyamides.

Comments on a potentially useful new monomer: 4-vinylbenzylcyclopentadiene

Synthesis of a new vinyl monomer based on cyclopentadiene (CP) has been attempted with the ultimate aim of exploiting the ability of CP to function as both a diene and a dienophile. It was considered that incorporation of the new monomer as a component of a copolymer could, in principle, promote cross-linking by the Diels-Alder (DA) reaction, and breakdown of cross-linking on heating could occur via the retro-DA reaction. This type of reaction is of relevance to the creation of functional polymers such as those needed in flexographic plate development, in the fabrication of novel printable substrates and in the formulation of curable coatings. In this work, a solution of sodium-CP was prepared and treated at 0°C under nitrogen with a solution of 4-vinyl benzyl chloride. After removal of the precipitated sodium chloride, the isolated liquid product was analysed by several techniques to disclose the presence of the new monomer 4-vinylbenzylcyclopentadiene (VBCP), its dimer and divinylbenzene-substituted CP. The content of VBCP plus its isomers was approximately 41%. Attempts to effect complete purification were not successful.

The pagodane route to dodecahedranes-unsaturated dodecahedranes, protection and deprotection

Monounsaturated, highly pyramidalized, highly reactive (i.a. dienophilic, dipolarophilic) dodecahedranes (2,10) are prepared from an adequately functionalized bisseco substrate. Cheletropic (-N2O; -SO2) and retro-DA reactions are probed as potential methodologies in the preparation of dodecahedrapolyenes.