Study On Improving The Toughness Of Photothiol-ene/Siloxane Hybrid System

The photopolymerization technology has attracted the attention of the majority of scientific researchers because of its advantages such as environmental friendliness,speed,and controllability in time and space,but it has the problems of oxygen polymerization inhibition and large volume shrinkage.The thiol-ene photopolymerization system has the advantages of antioxidant polymerization,small volume shrinkage,and delayed gelation,but also because of the existence of thio-ether bonds,the physical properties of the thiol-ene system,such as mechanical properties and the glass transition temperature is not satisfactory,the organic-inorganic hybrid system is considered as a possible solution,but there are fatal defects of very poor toughness.In this paper,the research work is carried out with the goal of understanding the influence of various factors on the toughness of the thiol-ene curing system,and then to design and study methods which can increase the toughness of the photo-thiol-ene/siloxane organic/inorganic hybrid system.This thesis proposes two methods.The first method is:one-step method of interpenetrating and superimposing the organic network formed by photopolymerization thiol-ene click chemistry and the inorganic network formed by hydrolysis of siloxane groups to form a thiol-ene/siloxane interpenetrating network to improve the toughness of the system and the glass transition temperature.The second method is to modify the polysiloxane containing a large amount of mercapto groups and inactivate the mercapto groups on it to reduce or even eliminate the crosslinking of the mercapto polysiloxane with the organic network.The modified mercapto polysiloxane is added to the photothiol-olefin species to form an organic network by ultraviolet light,and interpenetrate with the inorganic network to prepare a thiol-ene/siloxane interpenetrating network to improve the resilience of system.Research indicates:1.The results of multi-system and multi-variable studies show that the modulus of the mercaptan-ene photocuring system is affected by the functionality and structure of the mercaptan and ethylenic monomers used.Low functionality can reduce the crosslink density of the system,which in turn reduces the Young’s modulus of the system.And high flexibility can improve the deformation capacity of the system,thereby increasing the elongation at break.The Young’s modulus and elongation at break affect toughness.On this basis,a divalent mercaptan and a difunctional olefin are used as main components,and a small amount of a tetrafunctional mercaptan is used as a cross-linking point.A curing system with an elongation at break of up to 320%is obtained by photo click chemistry.But the toughness is still not good.2.Through photo-click chemical reaction of thiol and double bond,two new methoxysilane compounds with different functionalities with organic segment spacers were designed and prepared,hoping to reduce and improve the crosslink density of the inorganic network to enhances the toughness of the thiol-ene/siloxane organic/inorganic hybrid system.The results show that the addition of siloxane monomers with organic spacer segments in a high modulus organic system can effectively increase the elongation at break of the system by about 7 times,but the Young’s modulus of the system is greatly reduced.Adding a siloxane monomer with organic spacer segments to an organic system with a high elongation at break can greatly increase the modulus of the system,which can be increased by about 16 times,but the elongation at break is greatly reduced.Compared with the corresponding organic system,the overall toughness of the two hybrid systems is not improved.However,compared with the system using methoxysilane,the obtained curing system has a huge improvement in appearance morphology,Young’s modulus and elongation at break.3.Designed and prepared polysiloxanes with different pendant thiol content,hoping to be a species with very low thiol functionality,which can effectively adjust the curing system crosslink density in the photo-click chemical reaction,and can also strengthen the toughness through the internal plasticization of the polymer.The results show that the thiol retention rate is the best at 5%.Although the high modulus system can increase the elongation at break of the system by a maximum of about 11 times,it also reduces the modulus of the system,resulting in the toughness of the system decreases.But for the system with high elongation at break,it has the effect of improving toughness,the maximum increase is 58.9%,and the effect is remarkable.