Study On Modifying UV-cured Coatings And Synthesis Of Hyperbranched Polymers Through Thiol-click Polymerization

UV-curable coatings have developed rapidly in recent years due to their 5E advantages of efficient,environmental friendly,energy saving,economical and enabling.The largest proportion of UV-curable coatings is oligomers,and the most widely used oligomers are epoxy acrylate（EA）and polyurethane acrylate（PUA）.EA has the advantages of fast curing speed,high hardness and excellent chemical resistance.However,the density of rigid benzene rings in the molecular chain of EA is relatively high.And the content of unsaturated double bonds in EA is high,which results in the flexibility and adhesion of UV-curable coatings is poor.PUA has the advantages of good flexibility and chemical resistance,but the content of photosensitive groups in PUA is insufficient,resulting in the hardness of the UV-cured coatings is low.At present,hyperbranched polymers have great potential in the modification of UV-curable resins.The internal cavity of the hyperbranched polymer can improve the toughness of coatings,and the unique three-dimensional structure can effectively reduce the internal stress and the curing shrinkage rate of UV curing system.In addition,the hyperbranched polymer has a large number of active end groups,which can participate in the cross-linking of system and increase the hardness of coatings.In this thesis,a series of sulfur-containing hyperbranched polymers with adjustable backbone and functionally modified end groups were designed and synthesized based on thiol-click polymerization reaction.The relationship between the molecular structure and properties of sulfur-containing hyperbranched polymers was studied.Sulfur-containing hyperbranched polymers were used to modify the UV-curable resin,and the performance of UV-cured coatings were studied.The specific research contents are divided into the following three parts:（1）Trimethylolpropane tris（3-mercaptopropionate）（TMPMP）was used as the B₃monomer,and glycidyl methacrylate（GMA）was used as the AC monomer.The thiol-terminated hyperbranched polythioethers（HBP-SH）were synthesized by the thiol-methacrylate and thiol-epoxy click polymerization reaction.Then,HBP-SH was modified by tetrahydrofurfuryl acrylate（THFA）and furfuryl methacrylate（FMA）,and hyperbranched polythioethers were synthesized by a one-pot method.The main chain of hyperbranched polythioethers is polythioether,and the end groups are thiol,tetrahydrofuran or furan groups.In order to solve the problem of high brittleness and poor adhesion of UV-cured epoxy acrylate coatings,using hyperbranched polymers to modify epoxy acrylate is an effective method.Epoxy acrylate（EA）,reactive diluent,photoinitiator and hyperbranched polythioether were mixed uniformly.The hybrid resin was cured by UV light to prepare hyperbranched polythioether modified epoxy acrylate UV-cured coatings.The effects of end group modification types,end group modification ratio and addition amount of hyperbranched polythioether on the hardness,adhesion,mechanical properties and curing shrinkage of composite UV-cured coatings were systematically studied.The research results showed that when the terminal modification group of hyperbranched polythioether was FMA,modification ratio was 100%,and addition amount was 2 wt%,the performance of coating was the best.The pencil hardness of the best coating was 3H,adhesion was level 1,impact resistance was 51 cm,tensile strength was 34.9 MPa,elongation at break was 7.0%,and curing shrinkage was 4.5%.（2）Tris（3-mercaptopropionic acid）ester compound was used as the B₃monomer,isophorone diisocyanate（IPDI）was used as the AA’monomer.A represents the primary NCO attached to the aliphatic chain in IPDI,and A’represents the secondary NCO attached to the aliphatic ring.A series of hyperbranched polythiourethanes with adjustable backbone and end groups were synthesized by thiol-isocyanate click polymerization.The research results showed that when the molar ratio of B₃and AA’monomer was 1:0.8～1.0,the end groups of hyperbranched polythiourethane were thiol groups.When the molar ratio of B₃and AA’monomer was 1:2.2～2.4,the end groups of hyperbranched polythiourethane were isocyanate groups.The isocyanate-terminated hyperbranched polythiourethane intermediates were further modified with monohydroxy compounds.And a series of hyperbranched polythiourethanes whose end groups were acrylate,methacrylate or epoxy groups were synthesized.When the acrylate-terminated hyperbranched polythiourethane was cured with photoinitiator 1173,the tack-free time was 3 s,the pencil hardness was HB,the adhesion was level 1,the impact resistance was 50 cm,and the gel content was 93.7%.（3）Hydroxyethyl acrylate（HEA）and perfluoroalkyl alcohol were used to modify the above-mentioned isocyanate-terminated hyperbranched polythiourethane intermediates.A series of UV-curable fluorine-containing hyperbranched polythiourethanes were synthesized.In order to improve the hardness of polyurethane acrylate and impart hydrophobicity to the UV-cured coatings,polyurethane acrylate（PUA）,reactive diluent,photoinitiator,solvent and fluorine-containing hyperbranched polythiourethane were mixed uniformly.The hybrid resin was cured by UV light to prepare fluorine-containing hyperbranched polythiourethane modified polyurethane acrylate composite UV-cured coatings.The effects of terminal fluorine modification types,terminal fluorine modification ratio and addition amount of fluorine-containing hyperbranched polythiourethane on the hardness,abrasion resistance and water contact angle of the composite UV-cured coating were systematically studied.The research results showed that when the terminal fluorine modification monomer of the fluorine-containing hyperbranched polythiourethane was 2-perfluorooctylethanol,the terminal fluorine modification ratio was 50%,and the addition amount was 3 wt%,the performance of composite UV-cured coating was the best.The pencil hardness of the best coating was 4H,adhesion was 0 grade,friction resistance was 60 times,and water contact angle was 102.1°.