| Prepolymers commonly used in cationic UV curing systems are cycloaliphatic epoxy compounds and oxetane derivatives.Compared with cycloaliphatic epoxy compounds,oxetane derivatives are characterized by low toxicity,low viscosity,low volatility and low cost.However,they also have the disadvantage of poor photosensitivity,which limits further development and application.In this paper,after the hydrosilylation reaction between 3-ethyl-3-allylmethoxy oxetane(Allyl EHO)and1,3,5,7-tetramethylcyclotetrasiloxane(D4H),a novel kind of cationic prepolymer named 1,3,5,7-tetramethyl-2,4,6,8-tetra[(3-ethyl-3-methoxyoxetane)propyl]cyclo-tetrasiloxane(TMTEMPCS)was systhesised.UV-curing properties and stereolithography 3D printing experiments of the prepolymer were studied.The content of this article was roughly as follows:(1)Precursor 3-ethyl-3-hydroxymethyl oxetane(EHO)was prepared from diethyl carbonate and trihydroxypropane.After that,the EHO was reacted with allyl bromide,and the obtained product was characterized by FT-IR and ~1H-NMR.The results proved that the obtained product was Allyl EHO.In the experiment,if the molar ratio of EHO to allyl bromide was 1:1.2,and the reaction time was 24 h,then the yield of the product was the highest.(2)After the hydrosilylation reaction between Allyl EHO and D4H,the obtained product was characterized by FT-IR and ~1H-NMR.The results affirmed that the product was TMTEMPCS.The best reaction conditions were also studied in experiments.The molar ratio of Allyl EHO to D4H was 4.2:1.0,and the mass of Karstedt catalyst added was 0.25%of the mass of the two reactants.When the temperature of the mixed solution in the three-necked flask reached 85℃,dropwise of the mixed solution of D4H and toluene was added into flask to react for 3 h.After the dripping was over,the reaction was continued at 90℃-95℃for 6 h to obtain the product with a higher conversion.(3)Photosensitive resin was prepared by mixing the TMTEMPCS and cationic photoinitiator triarylsulfonium hexafluoroantimonate(UVI-6976).The cured films were prepared after photosensitive resin was cured.Afterwards,TG analysis and light transmittance test were performed on the cured films.The results revealed that the cured films reached the thermal decomposition peak at about 425℃,indicating good thermal stability.When the light wavelength was 350 nm to 800 nm,the light transmittance of the cured films was above 80%.UVI-6976 was added to E-51 epoxy resin and 2021p cycloaliphatic epoxy resin respectively,and the same proportion of photosensitive resin were prepared.After photo-DSC test,the results revealed that the photosensitive properties of the TMTEMPCS were better.A photosensitive resin of radical-cationic hybrid system was prepared by mixing the TMTEMPCS and the free radical reactive monomer epoxy acrylate JZ-101Q in the mass ratio of 1:1.Then the mechanical properties of the cured films were tested,giving 48.4 kg·cm of impact strength,1 mm of flexibility,50.38%of damping hardness,26.36 MPa of tensile strength,7.7%of elongation at break,2337.07 MPa of elastic modulus and 23.69MPa of flexural strength.At the same time,the TMTEMPCS and E-51 epoxy resin were mixed in the mass ratio of 1:1 to prepare cationic photosensitive resin.Then the mechanical properties of the cured films were also tested,giving 44.2 kg·cm of impact strength,1.5 mm of flexibility,56.57%of damping hardness,30.34 MPa of tensile strength,4.6%of elongation at break,3134.34 MPa of elastic modulus and27.81 MPa of flexural strength.(4)The synthetic TMTEMPCS,UVI-6976,polyether polyol and CYD-128epoxy resin were added together to prepare the photosensitive resin required for 3D printing.Using HRPL-150A Stereolithography Rapid Prototyping as the printing equipment,the printing temperature,laser power,layer thickness,scan spacing,foothold scan speed and parts scan speed were respectively set to be 32℃,150 mw,0.10 mm,0.08 mm,1000 mm/s and 1250 mm/s.According to the above conditions,printing parts had good mechanical properties. |
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