Study On Preparation And Properties Of Sulfur-containing Optical Materials With Flame Retardancy

The rapid development of optoelectronics field raises higher requirements for high-performance optical materials,such as high refractive index,excellent mechanical strength,good optical transparency,and outstanding flame retardancy,which can expand applications of optical materials.As important optical materials,polythiourethane and acrylate have received much attention,and improving their comprehensive performance is one of the current research hotspots.In this paper,based on the structure-property relationship,a variety of polythiourethane and acrylate optical materials with high refractive index,excellent flame retardancy and outstanding mechanical strength have been prepared by the methods of designing novel monomers and nanocomposites,and the mechanism on improving the overall performance of the materials has been explored.The main works are as follows:（1）A series of highly cross-linked polythiourethane were synthesized using thiols and isocyanates with different structures by thiol-isocyanate click reaction and studies on thermal,mechanical,optical properties and flame retardancy of polythiourethane were carried out to obtain the structure-property relationship.The results show that the greater the functionality of reactive groups and the more rigid groups of the monomer,the better the glass transition temperature and mechanical strength of polythiourethane,where the increasing order of the performance of polythiourethane was as this sequence:linear long-chain structure,alicyclic structure and benzene ring structure.However,too many rigid rings will lead to deterioration of material properties.The higher the content of sulfur atom and benzene ring in the monomer,the higher the refractive index of polythiourethane.Meanwhile,the synergistic effect of sulfur atom and rigid benzene ring improves the flame retardancy of polythiourethane.（2）Based on the structure-property relationship between sulfur atoms and cyclic P=N structure and materials,a cyclotriphosphazene derivative was developed for improving the optical,thermal and flame retardant properties of acrylate polymers.The results indicate that the glass transition temperature of binary copolymers increases from-14.4℃t o 37.4℃due to the presence of appropriate rigid P=N unit.Thanks to the presence of sulfur atom and P=N unit with high molar refraction in the derivatives,the refractive index of binary copolymers increases from 1.5185 to 1.5410.Owing to the catalytic carbonization of the high content of sulfur atoms and phosphazene rings,the binary copolymers and ternary copolymers have the limiting oxygen index of29.50%and 25.80%,respectively.（3）Composites show considerable potential for applications in high-performance polymers.Therefore,two phosphazene polymer nanoparticles（PZS-1 and PZS-2）were synthesized by water-triggered self-assembly method and ultrasonic method,and then two phosphazene/polythiourethane composites（PZS/PTU-1 and PZS/PTU-2）were prepared.Because of the good dispersion of two PZSs and their powerful covalent attachment and interfacial bonding with the matrix,the obtained PZS/PTU composites show the enhancement of overall performance,where their glass transition temperature and tensile strength reach 58.6℃and 82.62MPa（PZS/PTU-1）,59.9℃a nd 84.34 MPa（PZS/PTU-2）,respectively.Due to the contribution of P=N unit and sulfur atom with high molar refraction,the refractive index of the two composites increases to 1.6580,and the limiting oxygen index of the two composites increases to 21.39%and 21.10%,respectively.The preceding changes are due to the catalytic carbonization effect of PZS,the shielding effect of the formed high-expansion carbon layer and the dilution effect of the generated nonflammable gases during combustion.（4）Due to the powerful interfacial bonding between PZS and polythiourethane,the agglomeration of nano-Zr O₂ was improved.Characterization techniques such as TEM,SEM,FTIR and XPS all indicated the successful synthesis of the core-shell structure of Zr O₂@PZS nanoparticles.Furthermore,the comprehensive properties of nanocomposites obtained by introducing them into polythiourethane were studied.The results demonstrate that the cross-linked PZS with good dispersion can uniformly disperse Zr O₂into the matrix and the regular spherical core-shell nanoparticles present very close interfacial bonding with the matrix,forming a uniform and ordered cross-linked network structures.This nanocomposite exhibits a tensile strength of 79.28 MPa and a glass transition temperature of 62.8℃.Zr O₂@PZS/PTU nanocomposite with the highest Zr O₂ content shows a high refractive index of1.6590.Meanwhile,owing to the synergistic flame-retardant mechanism of the gas phase and the condensed phase,the nanocomposite shows a high limiting oxygen index of 25.39%.