Study On The Composition,Curing Process And Properties Of A Room Temperature-Curable Styrene-Free Unsaturated Polyester Resin

Traditional unsaturated polyester resin?UPR?products or matertials are usually prepared using about 30 wt%styrene?St?as a crosslinking component and methyl ethyl ketone peroxide/cobalt iso-octanoate as a room-temperature initiating system.Therefore,in the process of their processing and curing,there inevitably exist the harm to human health and the environment caused by styrene and the potential carcinogenic risk of cobalt-containing compounds.Undoubtedly,an effective strategy for solving this issue is to prepare styrene-free UPR products or materials by using a new initiating system in which a cobalt-free compound is used as an accelerator.Therefore,a low-volatility and low-toxicity macromolecular active monomer urethane acrylate?HEA-IPDI?was designed and synthesized;and the as-synthesized HEA-IPDI and commercially available acrylate monomer 1,6-Hexanediol diacrylate?HDDA?were used as a crosslinking component for UPR instead of St,thereby obtaining a mixed resin composed of UPR and non-styrene crosslinking components,UPR/HEA-IPDI/HDDA.The styrene-free cured UPR materials were prepared via the room-temperature curing reaction of the mixed resin UPR/HEA-IPDI/HDDA using pentaerythritol tetra-3-mercaptopropionate?PETMP?and Fe Cl₃as accelerators;and their preparation characteristics,physicomechanical properties,thermal properties and micromorphology were characterized and analyzed.The results of this study will lay a solid theoretical and experimental foundation for designing and preparing environmentally friendly styrene-free UPR products or materials,so as to fundamentally solve the problems inherent in a traditional UPR/St resin.The main content and results of this work are as follows.?1?The urethane acrylate with two terminal carbon-carbon double bonds,HEA-IPDI,was synthesized through the reaction of hydroxyethyl acrylate?HEA?and iso-phorone diisocyanate?IPDI?;HEA-IPDI and 1,6-hexanediol diacrylate?HDDA?were used as a crosslinking component for UPR and then a series of mixed resin systems with different compositions,UPR/HEA-IPDI/HDDA,were prepared.The curing of these mixed resins was initiated at room temperature by the methyl ethyl ketone peroxide/cobalt iso-octoate initiating system,thus preparing styrene-free cured UPR materials.The studies on the preparation and properties of these cured UPR materials indicate that the mixed resin UPR/HEA-IPDI/HDDA has low volatility and its viscosity can meet the requirements of the processing technology by adjusting its ratio reasonably.In the case of the same UPR content in the mixed resin UPR/HEA-IPDI/HDDA,as the HEA-IPDI content increases,the viscosity of the resin system will increase;accordingly,the physicomechanical properties,glass transition temperature?T_g?and heat distortion temperature?HDT?of the cured UPR material will also increase to a certain extent.For the mixed resin UPR/HEA-IPDI/HDDA with a mass ratio of 45:15:40,its viscosity is 1350m Pa·s,its volatile amount at room temperature is only 5.36%of the traditional UPR/St mixed resin;and the tensile strength,elongation at break,bending strength and impact strength of the corresponding cured UPR material are 41.7 MPa,3.4%,50.8 MPa and 7.0 KJ/m²,respectively,and its T_g and HDT are 85.0?C and 61.5?C,respectively.Compared with the cured resin UPR/St,the styrene-free cured UPR material exhibits relatively lower tensile strength and bending strength,better toughness and higher thermal stability.?2?In order to achieve the room-temperature curing of the mixed resin UPR/HEA-IPDI/HDDA without any cobalt compound as an accelerator,Fe Cl₃ and pentaerythritol tetra-3-mercaptopropionate?PETMP?were used to form the composite accelerator for UPR curing,and two new room-temperature initiating systems were designed by using methyl ethyl ketone peroxide?MEKP?and t-butyl peroxybenzoate?TBPB?as an initiator for UPR curing,namely the initiating system MEKP/PETMP/Fe Cl₃ containing a single initiator and the composite initiating system MEKP/TBPB/PETMP/Fe Cl₃ containing double initiators.Taking the mixed resin UPR/HEA-IPDI/HDDA with a mass ratio of 45:15:40 as the research object,the effects of different new room-temperature initiating systems were studied on the curing characteristics of the mixed resin,and the physicomechanical properties,thermal stability and micro-morphology of the cured UPR material.The results indicate that the designed new room-temperature initiating systems can make the curing of the mixed resin UPR/HEA-IPDI/HDDA proceed at room temperature;and the colorless and transparent cured UPR resin can be prepared by adjusting the compositions of each initiating system.In addition,the mechanical properties of the cured UPR material prepared by the composite initiating system MEKP/TBPB/PETMP/Fe Cl₃ are superior to those of the corresponding cured UPR material prepared by the initiating system MEKP/PETMP/Fe Cl₃.When using the composite initiating system MEKP/TBPB/PETMP/Fe Cl₃ where the dosage of MEKP,TBPB,PETMP and Fe Cl₃ are1.25 wt%,0.2 wt%,0.6 wt%and 0.3 wt%relative to the total mass of the mixed resin,respectively,the gel time of the mixed resin is 15.5 min,and the prepared cured UPR material is colorless and transparent and possesses relatively good mechanical properties.Its tensile strength,elongation at break,bending strength and impact strength are 38.1 MPa,6.3%,49.7MPa and 8.9 KJ/m²,respectively;and its T_g is 84.5?C.Its mass loss at 264.3?C is only 5%,exhibiting high thermal stability.