The effect of urea on the curing of urea formaldehyde resins

Отверждение карбамидоформальдегидных смол с различным мольным соотношением в системе карбамид : формальдегид протекает по разным механизмам. Так, при мольном соотношении карбамид : формальдегид 1 : 2 процесс отверждения направлен в сторону образования межмолекулярных связей – метиленовых и метиленэфирных, о чем свидетельствует снижение содержания гидроскиметильных групп. Введение в смолу карбамида до мольного соотношения карбамид : формальдегид 1 : 1,65 приводит к деструкции метиленэфирных связей под действием амидных групп карбамида, формированию на их месте метиленовых мостиков, образованию мономерных продуктов, которые включают в себя карбамид и его гидроксиметильные производные. Curing of urea-formaldehyde resins with different molar ratio in the system urea : formaldehyde flows through different mechanisms. Thus, at a molar ratio of urea : formaldehyde 1 : 2, the curing process is directed towards the formation of intermolecular bonds – methylene and methylene-ether, as evidenced by a decrease in the content of hydroksimethyl groups. The introduction of urea into the resin to the molar ratio urea : formaldehyde 1 : 1.65 leads to the destruction of methylene-ether bonds under the action of amide groups of urea, the formation of methylene bridges in their place, the formation of monomer products, which include urea and its hydroskimethyl derivatives.

Preparation and Characterization of Urushiol Methylene Acetal Derivatives with Various Degrees of Unsaturation in Alkyl Side Chain

Preparation of urushiol derivatives was carried out in response to the drug industry’s increasing demand for new synthetic anticancer agents. Urushiol methylene acetal derivatives were synthesized in high yields by reaction of urushiol with methylene chloride under the catalytic action of NaOH. Four kinds of urushiol methylene acetal monomers were separated by silica-gel column and preparative HPLC, and their structures were elucidated by extensive spectroscopic methods, including 1D-NMR and 2D-NMR (1H,13C-NMR,1H-1HCOSY, HSQC, and HMBC) as well as TOF-MS. They were identified as 3-[pentadecyl] benzene methylene ether (compound 1), 3-[8′-pentadecatrienyl] benzene methylene ether (compound 2), 3-[8′,11′-pentadecatrienyl] benzene methylene ether (compound 3), and 3-[8′,11′,14′-pentadecatrienyl] benzene methylene ether (compound 4). This research provides a theoretical reference for exploration of these interesting and potentially bioactive compounds.