Preparation Of Functional Polyurea Materials From Diisocyanate Monomers

As a high impact engineering material,polyureas?PU?have been widely used in protective coatings for different structural materials,because of their good thermal shock,abrasion resistance,flexibility and fast curing.Nowadays,PU materials are also used in many emerging fields.Precipitation polymerization became one of the most widely used methods in PU preparation and attracted wide attention because of the simple operation and easy product separation of the process.In this work,PU microspheres were prepared via precipitation polymerization of isophorone diisocyanate?IPDI?with melamine?MLE?as monomers in dimethyl sulfoxide?DMSO?.The microspheres were separated from the reaction system by simply filtering.In addition,the influences of different solvents,the amount of monomers and the reaction temperature on the formation of the microspheres were discussed.The size and morphology of the microspheres were characterized by scanning electron microscope?SEM?,and the chemical structure of microspheres was characterized by Fourier transform infrared spectra?FTIR?.The SEM photographs show that,with the mass ratio of DMSO/acetone at 1/1,1.5 wt%of the monomers relative to the solvent,PU microspheres,prepared by polymerization at 50oC,were of lower polydispersity?PDI,1.0263;Sphere diameter,2.01?m?.C=N stretching vibration peak?attributed to triazine ring of MLE?at 1554 cm^-1 and CH₂ asymmetric stretching vibration peak?attributed to those of IPDI?at 2924 cm^-1 were observed,a urea carbonyl absorption peak at 1656 cm^-1 was also detected,indicating that this sample was consisted of MLE and IPDI monomer units.Moreover,porous PU materials were prepared by precipitation polymerization of4,4'-diphenylmethane diisocyanate?MDI?with MLE.The effects of temperature on the morphology and chemical structure of the porous PU materials were discussed.The results showed that the specific surface area of the porous PU material was 14.758 m²/g with the pore volume of 0.0463 cm³/g.By comparing the FTIR spectra of PU samples prepared at different polymerization temperature,it was found that biuret might be generated in PU prepared at180oC.However,the low resolution of FTIR makes it difficult to have an accurate analysis of PU structure.Nitrogen-containing carbon materials were prepared at high temperature with PU material as precursor and N₂ protected.BET results showed that the specific surface area of the carbon material was 84.16 m²/g,with a pore volume of 0.076 m³/g.EDS results showed that,in the carbon material,the carbon content was 69.13%,and the nitrogen content was30.87%.Lithium ion battery was assembled with the carbon material as electrode.The capacitance per unit mass of the battery for the initial charge was 921.77 mA?h/g,and the charge-discharge efficiency was 44.1%.This study provides a new method for the preparation of nitrogen-containing carbon materials.Specially designed biuret-containing PU oligomers?BPU?were also prepared at 130oC with excessive isocyanate and characterized by NMR spectra(¹H,¹³C and ¹⁵N).By comparing the NMR spectra of these BPU samples with the PU samples prepared by polymerization of the diisocyanate in water,the results clearly confirm the existence of biuret group in BPU samples and the absence of biuret in PU samples prepared at 30oC.It was concluded that the poor solubility of PU in common organic solvents must be caused by the presence of abundant hydrogen bonding rather than by biuret crosslinking.This study provides a reliable method for the analysis of PU chemical structure.