Study On The Synthesis Of Photopolymrizable Disulfide Monomers And Its Reducing Volumetric Shrinkange And Regulating Polymer Properties

Photopolymerization technology is a green technology with high efficiency and simplicity and energy saving.However,free-radical photopolymerization system as the most widely used system in photopolymerization technology has been suffering from the high volumetric shrinkage.The volumetric shrinkage has great adverse effects on properties of materials,thereby severely limiting the application of the photopolymerization technology,especially for the applications that require materials with high precision and performances.Therefore,the reduction of volumetric shrinkage to improve the properties of photocured materials and to realize the regulation of structures and performances of polymers is of great significance.We have established a new strategy for reducing volumetric shrinkage during photopolymerization based on the nature of "cleavage and recombination"reversible nature of disulfide-bonds under UV light irradiation.We have designed and synthesized a series of photopolymerizable disulfide monomers that have capability of reducing volumetric shrinkage and regulating polymers structures and properties.The influences of the monomers structures on their photochemical properties and photopolymerization behaviors,and the volumetric shrinkage and properties of the polymer were systematically investigated to obtain the intrinsic relation between structure and performance,which provides a theoretical basis for the application of disulfide monomers in the photopolymerization field.This research has great theoretical significance and practical application value for photopolymerization and organic sulfide.The main research work and the conclusions:1.An aliphatic photopolymerizable disulfide monomer(2,2'-dithiodiethanol diacrylate,DSEA)was synthesized based on ?-mercaptoethanol and acryloyl chloride using H2O2/Nal oxidation coupling reaction.The photochemical properties,photo-degradation mechanism and initiating photopolymerization behaviors of DSEA were explored in detail by ultraviolet absorption spectroscopy,real-time infrared spectroscopy(RTIR),electron-spin resonance(ESR)and confocal micro-Raman spectroscopy.The results confirm that DSDA has two maximum absorption peaks at 246 and 325 nm,and can photocleave to produce thiyl radicals with the capability of initiating polymerization under UV light irradiation.And the number of thiyl radicals gradually increases with the increase of irradiation time.Moreover,some thiyl radicals undergo a reversible reaction or an exchange reaction to restore the disulfide bond to form the original or a new disulfide compound.Some thiyl radicals attack acrylate double bonds of monomers to initiate polymerization or combine with the carbon free radical in the system to terminate chain growth.In the presence of a photoinitiator,most generated thiyl radicals undergo disulfide-bond restoration and exchange reactions instead of initiating polymerization or chain termination.2.The influence of the DSEA on the volume shrinkage,physical and mechanical properties,thermal stability,and surface properties of tripropylene glycol diacrylate(TPGDA)UV-curable system were investigated in detail.The results indicate that the addition of DSDA can drastically decreases the volumetric shrinkage of the photopolymerization process through a repeated "contraction-expansion-contraction" volume-adjustable process.With the increase of DSEA content,the thermal stability,glass transition temperature and tensile strength of the photocured material were slightly decreased,but the homogeneity of the material is greatly improved,and the elongation at break,contact angle and surface hardness are increased.3.Three aliphatic photopolymerizable disulfide monomers with different structures were designed and synthesized to investigate the effect of their structures on their photochemical properties and photopolymerization behaviors,and properties of materials.The results demonstrate that with increasing the carbon chain length between acrylate group and disulfide bond of the disulfide monomer,the characteristic absorption peak of disulfide bond is blue-shifted,and the rate of thiyl radicals production based on disulfide bond cleavage under UV irradiation and the initiating activity of the thiyl radical are decreased.Moreover,the disulfide bond mainly occurs "cleavage and recombination" reaction.Furthermore,three aliphatic photopolymerizable disulfide monomers with different structures can significantly reduce the volumetric shrinkage during the free radical photopolymerization process.With the increase of carbon chain length between acrylate group and disulfide bond,the ability of disulfide monomers to reduce volume shrinkage are enhanced.With the increase of the content of the aliphatic disulfide monomer,the gel fraction,thermal stability and tensile strength of the material are slightly decreased,but the elongation at break of the material is improved.4.A kind of aromatic photopolymerizable disulfide monomer(ADSEA)was synthesized.The photochemical property and photopolymerization behavior of ADSEA were investigated by ultraviolet absorption spectroscopy and real-time infrared spectroscopy(RTIR).In addition,the influences of the ADSEA on the volume shrinkage,physical and mechanical properties,thermal stability of TPGDA photocurable systems were also investigated.The results show that disulfide bond of ADSEA exhibits an obvious absorption peak centered at 337 nm,and the absorption peak is remarkably red-shifted compared with aliphatic disulfide monomers.ADSEA can also produce aromaticity thiyl radicals with the capability of initiating photopolymerization by disulfide bond homolytic cleavage under UV irradiation.And the initiating activity of the aromaticity thiyl radical for TPGDA system is higher than that of the aliphatic thiyl radical.Also,the ADSEA can reduce the volume shrinkage,but the ability of ADSEA to reduce the volume shrinkage is lower than that of the aliphatic disulfide monomers.With the increase of ADSEA content,the gelation yield,thermal stability and tensile strength of the photocured material were slightly decreased,but the elongation at break of the material is enhanced.