Molecular Heterostructures of Covalent Triazine Frameworks for Enhanced Photocatalytic Hydrogen Production

Conjugated polymers have emerged as promising candidates for photocatalytic H₂ production owing to their structural designability and functional diversity. However, the fast recombination of photoexcited electrons and holes limits their H₂ production rates. We have now designed molecular heterostructures of covalent triazine frameworks to facilitate charge‐carrier separation and promote photocatalytic H₂ production. Benzothiadiazole and thiophene moieties were selectively incorporated into the covalent triazine frameworks as electron‐withdrawing and electron‐donating units, respectively, by a sequential polymerization strategy. The resulting hybrids exhibited much improved charge‐carrier‐separation efficiency as evidenced by photophysical and electrochemical characterization. An H₂ evolution rate of 6.6 mmol g^?1 h^?1 was measured for the optimal sample under visible‐light irradiation (λ>420 nm), which is far superior to that of most reported conjugated‐polymer photocatalysts.     

Visible‐Light‐Induced Passerini Multicomponent Polymerization

Herein, we introduce an additive‐free visible‐light‐induced Passerini multicomponent polymerization (MCP) for the generation of high molar mass chains. In place of classical aldehydes (or ketones), highly reactive, in situ photogenerated thioaldehydes are exploited along with isocyanides and carboxylic acids. Prone to side reactions, the thioaldehyde moieties create a complex reaction environment which can be tamed by optimizing the synthetic conditions utilizing stochastic reaction path analysis, highlighting the potential of semi‐batch procedures. Once the complex MCP environment is understood, step‐growth polymers can be synthesized under mild reaction conditions which—after a Mumm rearrangement—result in the incorporation of thioester moieties directly into the polymer backbone, leading to soft matter materials that can be degraded by straightforward aminolysis or chain expanded by thiirane insertion.     

An Alkenyl Boronate as a Monomer for Radical Polymerizations: Boron as a Guide for Chain Growth and as a Replaceable Side Chain for Post‐Polymerization Transformation

The ability of isopropenyl boronate pinacol ester to serve as a monomer in radical polymerizations was established and exploited for the synthesis of polymers that are difficult to access using other polymerization techniques. Although the monomer exhibits an α‐methyl‐substituted unconjugated structure, which is usually unfavorable for radical propagation, both free and controlled radical polymerizations smoothly afford the corresponding polymers. A density‐functional‐theory‐based investigation revealed that the boron atom moderately stabilizes the radical species, which leads to the suppression of the degradative chain transfer to the α‐methyl groups, and thus guides the reaction towards the radical polymerization. The boronyl pendants, which are directly attached to the polymer backbone, can be replaced with ‐OH or ‐NH₂ to yield poly(α‐methyl vinyl amine) or poly(α‐methyl vinyl alcohol), which has been inaccessible by conventional synthetic methods.     

Pigment encapsulation by emulsion polymerisation,redespersible in water

Emulsion Polymerization was carried out in the presence of inorganic pigments such as TiO2, black FexOy, yellow FexOy, and red FexOy, and NP 30 as surfactants, and water soluble AZO compounds or KPS as initiator. Monomers with specific hydrogen bonding interaction must be used in the initial steps of polymerisation, methylmethacrylate and vinylacetate being the most convenient. Then a semi continuous feed of a mixture of monomers was carried out in starved conditions. In order to make the covered pigments water-redispersible a mixture of hydrophobic and hydrophilic monomers should be chosen with proper pH conditions. The amount of surfactant has to be chosen so that no agglomeration of the covered pigments take place. The covered pigments were dried upon lyophylisation, then formulation of powder paints was carried out using commercial powder binders and other additives. Good properties of the paints, such as brightness were obtained in that way.     

Crosslinked plastic scintillators: A new detection system for radioactivity measurement in organic and aggressive media

The measurement of radioactive solutions containing organic or aggressive media may cause stability problems in liquid and plastic scintillation (PS) techniques. In the case of PS, this can be overcome by adding a crosslinker to the polymer structure. The objectives of this study are to synthesise a suitable crosslinked plastic scintillator (C-PS) for radioactivity determination in organic and aggressive media. The results indicated that an increase in the crosslinker content reduces the detection efficiency and a more flexible crosslinker yields higher detection efficiency. For the polymer composition studied, 2,5-diphenyloxazole (PPO) is the most adequate fluorescent solute and an increase in its concentration causes little change in the detection efficiency. The inclusion of a secondary fluorescent solute 1,4-bis-2-(5-phenyloxazolyl) benzene (POPOP) improves the C-PS radiometrical characteristics. For the final composition chosen, the synthesis of the C-PS exhibits good reproducibility with elevated yield. The obtained C-PS also displays high stability in different organic (toluene, hydrotreated vegetable oil (HVO) and methanol) and aggressive media (hydrochloric acid, nitric acid and hydrogen peroxide). Finally, the C-PS exhibits high detection efficiency both in water and in aggressive media and can also be applied in organic media showing similar or even higher detection efficiency values.     

Synthesis, polymerisation and degradation of poly(lactide-co-propylene glycol) dimethacrylate adhesives

Fluid ABA triblock poly(lactide-co-propylene glycol-co-lactide)s with 7, 17 or 34 propylene glycol and 2, 4, or 8 lactic acid units in each B and A block, respectively, end capped with methacrylate groups were prepared and polymerisation rates upon blue light exposure for 60, 120 or 240 s using 0.5, 1 or 2 wt.% initiators determined. The shortest monomer formulation, with 0.5 wt.% initiators, was most promising as an injectable degradable adhesive for biomedical applications, achieving 96% polymerisation by 120 s after the start of 60 s illumination, forming then a semi-rigid polymer that in water released linearly with time poly(methacrylic-co-lactic) acid degradation products. Over 14 weeks, 2 mm thick specimens largely maintained their dimensions as water sorption balanced the 19 wt.% material loss. Raising initiator concentration or monomer length reduced polymerisation rate on the lower surface of samples. Increasing the number of lactic acid units in each A block from 2 to 8 also enhanced photocrosslinked polymer water sorption and increased average total mass loss to 60 wt.% over 14 weeks but acid product release rate decreased with time. Monomers produced with longer polypropylene glycol B blocks required longer periods of light exposure for full cure and the final polymers exhibited slower non-linear hydrolytic degradation.