Application Of Lossen Rearrangement In Self-crosslinking Acrylate Coatings

Isocyanate(-NCO)group is a highly reactive group.With the development of polyurethane,polyurea and other materials,isocyanate has also been studied intensively.Lossen rearrangement is a method to prepare isocyanate using N-acetoxy amide group,which has the advantages of environmental friendliness and mild reaction conditions.Acrylic coatings have the advantages of good transparency,good weather resistance,but there are also shortcomings such as being brittle at low temperature and sticky at high temperature.If the groups of N-acetoxy amide and the groups containing active hydrogen are constructed into the molecular structure of acrylate resin,after resin molding,using Lossen rearrangement reaction under specific conditions,in-situ production of-NCO group,and the reaction with groups containing active hydrogen,can form carbamate-containing three-dimensional cross-networking structures,so as to improve the performance of acrylate resin.Based on this,the main research content of this paper is as follows:(1)N-acetoxymethyl acrylamide(AMAA)monomer was prepared using methyl methacrylate(MMA)as starting material.Lossen rearrangement of AMAA could occur under heating condition and isocyanate group was generated in situ.The monomer AMAA and hydroxyethyl methacrylate(HEMA)were introduced into acrylate copolymer.At a certain temperature,the AMAA structural unit in the copolymer will undergo Lossen rearrangement reaction to generate isocyanate groups in situ,and cross-link with the hydroxyl group in HEMA structural unit.Self-crosslinked acrylate copolymer has been prepared.(2)Self-crosslinking acrylate copolymer was applied to modified acrylate coatings.Solvent acrylate coatings were prepared by solution polymerization,and two environment-friendly acrylate coatings with low VOC content were prepared by emulsion polymerization and phase transformation.The structures of the polymers were analyzed by Fourier transform infrared spectroscopy(FT-IR),~1H NMR and gel permeation chromatography(GPC).In solvent-based acrylic coatings.The effects of temperature and catalyst DBTDL on the rearrangement crosslinking reaction,the content of crosslinking monomer on the properties of the paint film and the change of the properties of the paint film before and after crosslinking were studied.The results show that the degree of crosslinking reaction increases with the increase of temperature,and the reaction of the crosslinking monomer is basically complete at140℃for 12 h without catalyst.DBTDL can promote the crosslinking reaction and reduce the reaction temperature,but affect the paint film adhesion.The properties of the film after crosslinking were significantly improved compared with those before crosslinking.When AMMA content of crosslinking monomer is 15 wt%,the performance of crosslinking film is excellent.The effect of crosslinking reaction and the content of crosslinking monomer on the properties of environment-friendly acrylic coatings was studied.The paint film obtained by phase transformation method,when AMMA content of crosslinked monomer was 15 wt%,the adhesion after crosslinking was grade 1,2H pencil hardness,excellent water resistance,water contact Angle of 92.0°,the overall performance of paint film is the best.(3)The water resistance and alcohol resistance of the isocyanate group produced by rearrangement in the polymer were studied at different temperatures and times.The results show that the-NCO in the polymer has a certain water and alcohol resistance at room temperature,and can be used in some scenes in contact with water and alcohol;At 40℃and above,the-NCO in the polymer is unstable in water,but has some stability in commonly used alcohols.