Abstract. The curing of bisphenol A-aniline based benzoxazine was studied applying different accelerators (4,4"-thiodiphenol, o-dianisidine, 2-mercaptobenzimidazole and 4-mercaptophenol) to initiate the catalytic ring-opening of benzoxazine. Possible pathways of benzoxazine ring-opening, polymerization and cross-linking without and with the addition of different accelerators are presented. The curing kinetics was investigated by model-free kinetic analysis of experimental data obtained by differential scanning calorimetry (DSC). The addition of different accelerators significantly reduced the onset temperature of curing in dynamic experiments. The effects of accelerators on the results of isothermal conversion prediction were studied and discussed in detail. Among the used accelerators, thiodiphenol showed the best accelerating efficiency and was consequently used in further studies, where its amount was varied. By low heating rate DSC analysis the catalytic ring-opening, thermally accelerated ring-opening and the diffusion-controlled steps were identified. The amount of added accelerator affected particularly the ring-opening and diffusion-controlled steps.
Abstract. The Diels-Alder reaction between N-phenylmaleimide and benzoxazine bearing furan group was investigated for the purpose of successful appliance of self-healing in benzoxazine polymer networks. The reaction as a function of temperature/time was performed in molten state and in a solution, where also the kinetic study was performed. The Diels-Alder reaction leads to a mixture of two diastereomers: endo presented at lower cyclo-reversion temperature and exo at higher. Therefore, the conversion rates and exo/endo ratio were studied in detail for both systems. For instance, in molten state the Diels-Alder reaction was triggered by the temperature of the melting point at 60°C with exo/endo ratio preferable to the endo adduct. The study of the kinetics in a solution revealed that the Diels-Alder reaction followed typical bimolecular reversible second-order reaction. The activation energies were close to the previous literature data; 48.4 and 51.9 kJ·mol -1 for Diels-Alder reaction, and 91.0 and 102.3 kJ·mol -1 for retro-Diels-Alder reaction, in acetonitrile and chloroform, respectively. The reaction equilibrium in a solution is much more affected by the retro-Diels-Alder reaction than in a molten state. This study shows detailed investigation of DA reaction and provides beneficial knowledge for further use in self-healing polymer networks.
A process for providing intermediate compounds as building blocks for effectively producing statins is described. The presented process is based on acetoxyacetaldehyde and acetaldehyde as substrates, which are presented in an aldol reaction catalyzed by a crude deoxyribose-5-phosphate aldolase (DERA) expressing culture lysate. Different addition regimes of both reactants into a reaction mixture were applied. For the highest concentration of product ((2S,4R)-4,6-dihydroxytetrahydro-2Hpyran-2-yl)methyl acetate, in the presented crude DERA expressing culture lysate-catalyzed reaction used further in the production of statins, the best addition time of reactants is described. Improved process conditions and reactants' feeding regime were achieved by converting a batch reaction to a fed-batch process, reaching the highest concentration of product ((2S,4R)-4,6dihydroxytetrahydro-2H-pyran-2-yl)methyl acetate near 77 g/L. The complete process was designed in a practical and economical manner and could be used further on an industrial scale.
The role of bacteriophage therapy in medicine has recently regained an important place. Oral phage delivery for gastrointestinal treatment, transport through the stomach, and fast release in the duodenum is one of such applications. In this work, an efficient polyHIPE/hydrogel system for targeted delivery of bacteriophages with rapid release at the target site is presented. T7 bacteriophages were encapsulated in low crosslinked anionic nanocellulose-based hydrogels, which successfully protected phages at pH < 3.9 (stomach) and completely lost the hydrogel network at a pH above 3.9 (duodenum), allowing their release. Hydrogels with entrapped phages were crosslinked within highly porous spherical polyHIPE particles with an average diameter of 24 μm. PolyHIPE scaffold protects the hydrogels from mechanical stimuli during transport, preventing the collapse of the hydrogel structure and the unwanted phage release. On the other hand, small particle size, due to the large surface-to-volume ratio, enables rapid release at the target site. As a consequence, a fast zero-order release was achieved, providing improved patient compliance and reduced frequency of drug administration. The proposed system therefore exhibits significant potential for a targeted drug delivery in medicine and pharmacy.
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