Preparation And Properties Of UV-curable Hyperbranched Polyurethane Coatings

Hyperbranched polymers (HBP) is a class of highly branched, a large terminal groups ellipsoidal macromolecules. In recent years, because of its unique structure, physical and chemical properties, the hyperbranched polymer become one of hot research fields. Compared with conventional linear polymers, a hyperbranched polymer has a plurality of terminal functional groups which can be modified, good solubility, low viscosity of solution or melt. Above-mentioned characteristics of hyperbranched polymers meet requirement of the UV-curable coating film formation for high molecular weight oligomers, the high degree of crosslinking, high functionality and low viscosity, etc, so that the hyperbranched polymer became a kind of ideal matrix resin material in UV curable coatings field. And hyperbranched polymers can be prepared by quasi-one-step or one-step synthesis method, which is more convenient to industrial product.In this research, a new BC2type monomer was prepared by ethylene diamine and2,2-bis (hydroxymethyl) propionic acid (DMPA) at ratio of1:1. The waterborne hyperbranched polyurethanes (WHBPU) were synthesized by BC2and the A2monomer toluene-2,4-diisocyanate (TDI), and a hydrophilic group was introduced by DMPA as hydrophilic agent. Then the WHBPU was modified by hydroxyethyl acrylate and TDI, so that its terminal functional group possessed the unsaturated bonds. The UV-curable waterborne hyperbranched polyurethane(UV-WHBPU) emulsion was prepared by neutralizing and water dispersing.According to pseudo one-pot procedure, the novel structure WHBPU be prepared in ice-salt bath (-5℃) reaction2h, and then60℃oil bath for2h and the structure of WHBPU was characterized. UV-WHBPU be obtained in oil bath at40℃. UV-WHBPU emulsion viscosity reached minimum when carboxyl content at1.34mmol/g. Triethylamine as a neutralizing agent and solids content of40%, the emulsion color milky, and it had the moderate viscosity and the best stability UV-WHBPU added20%of2-Hydroxyethyl acrylate as reactive diluent and2%photoinitiator, was dried2h at room temperature (25℃) then50℃for2h, its filming curing rate was relatively faster and the gel content of the film was maximum. When the4th generation UV-WHBPU and possessed80%of terminal double bond used as a film-forming oligomers, the hardness and adhesion of the film was higher, and the performance better.