Study Of UV-Curable Systerm Based On Dipentaerythritol And Derivatives

As an environmental friendly technique in material preparing and processing,UV curing has been widely used in leather,wood,metal surface coatings,glass surface coatings and many other fields.Different application fields require unique coating composition and UV curing conditions.The properties of cured coating mainly depend on the composition and structure of UV curing materials.Therefore,the researches on the relationship between properties of UV-cured film and structure of oligomer,the proportion of soft and hard segments,the density and distribution of photoactive groups and so on are very important and significant.From the perspective of molecular design,a series of star-shaped acrylates and urethane acrylates were synthesized from dipentaerythritol,acrylic acid,hydroxyethyl methacrylate?HEMA?,polyethylene glycol,ethylene carbonate and isophorone diisocyanate?IPDI?as raw materials in this paper.While the effects of functionality,density and distribution of double bonds on UV-curing reaction were investigated,and the details contents and results are as follows:Syntheses of class A acrylates:Under promotion of K₂CO₃ at 140?,6 and 12-ethoxylated dipentaerythritol,containing 4.2 mol%and 10.0 mol%carbonate unit,were synthesized from the reaction of dipentaerythritol and ethylene carbonate at the molar ratio of 1:6 and 1:12,respectively.The dipentaerythritol acrylates mixtures 1 or 2 with molar ratio of DPPA to DPHA being 52%,48%and 29%,71%were synthesized from dipentaerythritol and acrylic acid catalyzed by CH3SO3H at the molar ratio of dipentaerythritol and acrylic acid being 1:5.5 and 1:6.2,respectively.Then,the ethoxylated dipentaerythritol hexa-acrylates was synthesized by the reaction of ethoxylated dipentaerythritol with acrylic acid at the molar ratio of 1:6.2.Synthesis of class B acrylates:Multifunctional acrylate carbamate derivatives such as TFA1,TFA2,TFA3,were prepared from the hydroxy of dipentaerythritol penta-acrylate in mixture 1 with IPDI or polyurethane prepolymer obtained by the reaction of PEG-400,EPO-3000 with IPDI,respectively.Synthesis of class C acrylates:Isocyanate terminated acrylates,synthesized from the reaction of HEMA with IPDI or polyurethane prepolymer,reacted with 6-ethoxylated dipentaerythritol to form star-shaped urethane penta-acrylate and hexa-acrylate.The urethane penta-acrylate reacted further with polyurethane prepolymer to produce a series of multifunctional urethane acrylate with specific structure and different distribution of acrylates.The structures of so prepared products were characterized by ¹H NMR and FT-IR.The kinetics of UV-curing process was monitored by Fourier transform infrared?FT-IR?.The relationships between the structure of the multifunctional acrylates and UV-curing properties such as dry time,hardness,gel content,flexibility,and adhesion were further investigated.The results show that:proper introduction of ethoxy soft segment,which reduce double bond density of multifunctional acrylates,will significantly improve the flexibility of the cured film without decrease the film hardness.Compared with class A acrylates,at the same content double bond density,the flexibility of cured film coming from class B acrylates with longer soft segment is better.Further,the distance between the acrylate groups increases,the UV-curing rate of class C acrylate declines.By adjusting the content of diluent and the proportion of soft segments and carbamate unit,the hardness and flexibility of photo-curing film can be tuned to meet general requirement.