Study On The Photoinitiated Process Of Thiol-Ene Without Initiator And The Properties Of Photoreaction System

The thiol-ene photopolymerization system has the advantages of fast reaction speed,low oxygen inhibition and low volume shrinkage.What’s more,thiols and alkenes can photopolymerize without adding photoinitiators,which can effectively avoid the odor and toxicity problems caused by photoinitiator fragments in traditional photopolymerization.Thiols can absorb light around254 nm to break the S-H bond and generate sulfur radical,which can initiate thiol-ene photopolymerization.In addition,the light source with the main emission wavelength of 365 nm had also been found to initiate efficient thiol-ene photopolymerization.However,due to the mismatch between this band and the absorption spectrum of thiols,it is controversial that whether 365 nm light plays a key role in thiol-ene photopolymerization.The purpose of this thesis is to explore the role of 365 nm light in the process of S-H bond cleavage in thiols,and to evaluate the feasibility of using thiols to replace traditional photoinitiators to initiate the chain polymerization of acrylate systems for the purpose of reducing the adverse effects of traditional photoinitiator residues on the material.The main works are showed as follows:Firstly,two types of thiol-ene photopolymerization systems were designed:pentaerythritol tetrakis(3-mercaptopropionate)(PETMP)was mixed with alkene monomers as system I;1-dodecanethiol(NDM)was mixed with alkene monomers as system II.The photopolymerization kinetics behavior of these different thiol-ene systems without adding photoinitiator were studied under the irradiation of five light sources(254 nm LED light source,full-band high pressure mercury lamp,high pressure mercury lamp with 320-500 nm filter,365 nm LED light source and365 nm LED light source with 366 nm filter)to explore the effect of 365 nm light on the cleavage of S-H bonds in thiols.Secondly,pentaerythritol tetrakis(3-mercaptopropionate)(PETMP),1-dodecanethiol(NDM),pentaerythritol tetramercaptoacetate(PT)and benzylthiol(BMP)are used as thiol initiators,the traditional commercial photoinitiator 651 is used as a control group.Two light sources(254 nm LED light source and full-band high-pressure mercury lamp)were chosen to investigate the photopolymerization performance of acrylate monomers(such as the rate and conversion of polymerization,the molecular weight and the mechanical properties of materials)while the thiol is added as the amount of initiators.The main conclusions are showed as following:1.The results of the polymerization kinetics of the initiator-free thiol-ene system under five light sources show that it is difficult for the thiol-ene system studied to directly use 365 nm light to cleave the S-H bond to generate a sufficient amount of sulfur radicals to initiate the polymerization.Even though365 nm light can initiate thiol-ene photopolymerization,the light that actually plays a key role in the polymerization is a small amount(or even a very small amount)of 254 nm light radiated by the light source,while 365 nm light is very important for initiating thiol-ene system.The response did not play a significant role.2.Exploring the kinetics of photopolymerization of acrylates initiated by thiols as initiators found that a 254 nm light source can effectively narrow the gap between thiols and commercial initiator 651 in terms of the rate of initiating polymerization,even at very low light intensity(1 m W/cm~2),only 1 mol%of thiol can rapidly increase the polymerization rate of acrylate,and the higher the content of thiol,the higher the photopolymerization rate and conversion rate of acrylate,and the initiation effect is comparable to that of commercial photoinitiator 651,with commercial application value.3.The polymerization products initiated with thiols as photoinitiator have greater controllability in molecular weight and other properties,and can achieve thermal stability and glass transition temperature essentially the same as traditional photoinitiators.4.The acrylate system initiated by thiols can prepare polymer materials,which effectively avoids the phenomenon of low light transmittance and high yellowing caused by cracking fragments of traditional initiators.The field of yellowing has application advantages.