Study On Photoinitiated Frontal Radical Polymerization Of Unsaturated Polyester

UV curing technology is suited to cure thin surface such coatings and binders due to the limited penetration of ultraviolet?UV?light.As a kind of general method,heat polymerization always used in the thick system,however,it has the disadvantage of long reaction time-comsuming,large energy consumption and uneven heat dissipation,etc.Frontal polymerization is a new reaction mode with fast and energy saving,and the polymerization can proceed using its own exothermic effect.Here the autocatalysis unsaturated polyester resin system was designed,and the unsaturated polyester was polymerized without thickness restrictions at room temperature by UV-ignited frontal polymerization method.The autocatalysis vinyl ester resin?VE?reaction system was designed in the present of the compound initiator constitute of benzyl dimethyl ketal?BDK?photoinitiator and dibenzoyl peroxide?BPO?thermal initiator.The unsaturated polyester was polymerized quickly at room temperature when undergoing self-propagating UV-ignited frontal polymerization.The influences of reactive diluent,photoinitiator and thermal initiator on the frontal velocity and the frontal maximum temperature of were researched,respectively.The results show that,the frontal advance rate and the frontal maximum temperature raised with increasing the contents of reactive diluent and thermal initiator,and it is independent of the contents of photoinitiator.The front velocity is 1.25 cm/min and the front maximum temperature is 113.2?at the optimal ratio.Comparing with the heat polymerization product of VE resin composition,the frontal polymerization product exhibits better thermal stability and the higher glass transition temperature,and the surface hardness is increased from 76 HD to 82 HD.The VE resin cured product obtained by frontal polymerization has a continuous and dense structure by scanning electron microscope?SEM?.The thermal oxidation decomposition kinetics of the VE resin cured product by frontal polymerization was studied.The results show that the thermal oxidation decomposition process is divided into three stages,and the average activation energies???₁,???₂,and ???₃ of each stage are 113.34 k J/mol,243.65 k J/mol and 138.19 k J/mol,respectively,which calculated by the Kissinger equation and the Flynn-Wall-Ozawa equation.It shows that the material has good thermal oxidative stability and can undergo the higher thermal oxidation decomposition energy.The autocatalysis polyester acrylate?PEA?reaction system was designed,and the self-propagating rapid deep curing of the system was realized at room temperature using UV-ignited frontal polymerization method.The influences of reactive diluent,photoinitiator and thermal initiator on the frontal velocity and the frontal maximum temperature of were researched,respectively.The results show that the frontal velocity and the frontal maximum temperature increase with the content of reactive diluent and thermal initiator,and with the increase of the content of photoinitiator,the frontal velocity and the frontal maximum temperature did not show a significant upward and downward trend.At the optimal ratio,the front velocity is 1.4 cm/min,and the front maximum temperature is 113.3?.The thermal properties were analyzed by TGA and DSC.Compared with traditional thermal curing method,the thermal stability and the T_gtemperature of the PEA resin cured by the frontal photopolymerization method are higher.and the T_gof the frontal photopolymerization product and the traditional heat polymerization product are respectively 86?and 78?.The surface hardness of PEA resin cured product obtained by UV-ignited frontal polymerization method is 66HD,which is 6.45%higher than that of traditional heat polymerization product.The morphology of PEA resin cured product were observed by SEM and the results shown that no material defects such as cracks and pores were found even magnify 3000 times.The thermal oxidation decomposition kinetics of the PEA resin cured product obtained by frontal photopolymerization were studied,and the results showed that the material undergoes thermal oxidation decomposition in two stages.Combining the Kissinger equation and Flynn-Wall-Ozawa equation,the average activation energies???₁ and ???₂of the two thermal oxidation decomposition stages are calculated as 114.11 k J/mol,125.87 k J/mol,indicating that the polymer material only decomposes at a higher energy,i.e.,its thermal oxidative stability is better.