【Objective】Temperature and solid content significantly influence the molecular weight and chemical structure of pre-curing urea formaldehyde resins, playing an important role in regulating pre-curing behavior.【Method】Gel chromatography(GPC)and 13C-NMR were used to investigate the effects of temperature and solid content on the molecular weight distribution and main functional groups of pre-curing urea-formaldehyde resins, as well as the relative amounts of methylol, dimethylene and dimethylene ether groups. 【Result】At constant pre-curing time, Mn and Mw increased with increasing curing temperature, with the content of dimethylene ethers initially increasing and then decreasing, whereas the content of terminal and linear methylol groups decreased and that of linear and network dimethylene groups increased. The molecular weight of higher-solid-content resins was higher than that of lower-solid-content ones, with insignificant differences observed between the former resins. Although the content of linear methylol, dimethylene and dimethylene ether groups slightly increased with increasing solid content, the total number of terminal methylol groups was unchanged. 【Conclusion】Temperature had a much more significant effect on the pre-curing of urea-formaldehyde resins than their solid content, as determined by comparing the contents of methylol, dimethylene, and ether functional groups.
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