Study On The Molecular Structure Designing And Performance Of Transparent Polycarbonate-based Polyurethane Films

With the rapid development of science and technology and the increasing awareness of environmental protection,the market demand for optical polymer materials with high-performance increase.Transparent polyurethane(PU)films with unique chain structure and aggregate structure,which combined the excellent mechanical properties of PU and good optical properties,can be widely used in many fields such as photovoltaics,optical instruments,protection,automotive,electronics and so on.At present,the research on transparent polyurethanes mainly focuses on polyester polyurethanes and polyether polyurethanes.Polyester polyurethane has high polarity ester group,which cause crystallization and reduce its transparency.The molecular chain interaction force of polyether polyurethane is weaker,which lead to the random arrangement and low crystallinity causing high transparency.But it has the disadvantage of low cohesive strength,poor mechanical strength,poor UV resistance and solvent resistance.Moreover,polyurethane has problems such as poor temperature resistance,flammability,and melt dripping,which severely limits its application range.Therefore,it is an important issue for studying on transparent polyurethane films with high-performance.According to the relationship between the structure and properties of the polymer,highly transparent polycarbonate-based polyurethane(PCU)films were prepared by molecular structure design and raw material selection of polycarbonate diols in this work.The structure and properties of PCU films were systematically studied.Meanwhile,in order to broad the application range,PCU films were modified to have special properties,such as heat resistance and flame resistance.The specific research work are as follows:1.According to the transesterification method used in the synthesis of aliphatic polycarbonate diols(PCDLs)and the catalytic mechanism of the catalyst,the high-efficiency environment-friendly Mg-Fe/Ti LDHs acid-base dual-function catalyst were synthesized by introducing Ti element into Mg-Fe LDH catalyst,adjusting the acid-base matching strength.The bifunctional catalyst was applied in the synthesis of PCDLs.The crystal structure,microstructure,pH value,formation mechanism and catalytic activity of Mg-Fe/Ti LDHs catalysts were characterized and analyzed by XRD,FTIR,TEM and pH value test.The results show that the synthesized Mg-Fe/Ti LDHs catalysts have a typical layered structure with both protonic acid sites and Lewis base sites.As the amount of Ti increases,the alkalinity of the catalyst decreases,the acidity increases,and the synergistic catalytic effect increased first and then decreased.2.According to the principle of molecular structure design on transparent polyurethane,a series of aliphatic PCDLs with different structures and molecular weights were synthesized by two-step transesterification method using self-made Mg-Fe/Ti acid-base bifunctional catalyst.Molecular structure,hydroxyl value,moisture content,crystallization behavior,molecular weight,molecular weight distribution and viscosity of bi-polycarbonate and PCDLs were characterized and analyzed by FTIR,~1H NMR,GPC,DSC,moisture test,hydroxyl value determination and viscosity test.The results show that the controllability of the molecular weight of synthetic PCDLs can be improved by two-step transesterification method.PCDLs with random copolymerization and good transparency were synthesized by multi-component copolymerization,which can effectively reduce the symmetry of PCDLs molecular chains and break the internal regular order structure.PCU films with good optical properties were synthesized by self-made PCDLs.In addition,the transmittance of the PCU films were further improved by the composite chain extenders.The cyclohexane ring structure in PCDLs can avoid deterioration of the mechanical properties of PCU films,which caused by poor symmetry of the PCU molecular chain.Meanwhile,the heat resistance was improved.3.A serious of transparent PCU were synthesized by different self-made aliphatic PCDLs,IPDI and 1,4-BDO(or composite chain extender 1,4-BDO/PG)through a stepwise addition solution method.Transparent PCU films with uniform thickness and no appearance defects were prepared by self-made film forming device.The structures and properties of PCU films were characterized and analyzed by FTIR,WAXD,AFM,TGA,DSC,DMA,mechanical properties test,light transmittance test,yellowness index test,water absorption test,static contact angle test and shape memory performance test.The effect of R values,soft and hard segments content,molecular structure of PCDLs,different molecular weight of PCDLs and chain extenders on the structure and properties of transparent PCU films were systematically studied.The results shown that the transparency of PCU films with high performance and a certain degree of microphase separation were obtained by PCDLs,which were synthesized by random copolymerization.4.Based on the systematic study of the relationship between the structure and properties of transparent PCU films,the formulation of PCU film with best performance was selected.A series of transparent FPCU with high thermal resistance were synthesized based on self-made aliphatic PCDL,IPDI and compound chain extenders(1,4-BDO,PG and BPAF).The structure and properties of transparent fluorinated PCU films were characterized and analyzed by FTIR,WAXD,AFM,TGA,DSC,DMA,transmittance test,mechanical property test,yellowness index test,and static water contact angle test.The effects of fluorine content on the structure,optical properties,yellowing properties,thermal properties,mechanical properties and hydrolysis resistance of FPCU films were investigated.The results show that the introduction of fluorine enhances the heat resistance and hydrophobicity of the transparent FPCU film.5.According to the idea of?"organic-inorganic flame retardant compounding" and composite modification technology,the ultra-fine treatment of ammonium polyphosphate(APP)was carried out first,then the ultra-fineized APP is modified by amino silane coupling agent.An intumescent flame retardant(CAPP)having high thermal stability and good compatibility with polyurethane was obtained.The structure and properties of CAPP were characterized and analyzed by FTIR,XPS,SEM,TGA and particle size distribution.The formation mechanism of CAPP was discussed.Transparent PCU films with good flame retardancy was prepared by self-made inorganic CAPP flame retardant and the organic halogen-free flame retardant(600R).The structure,optical properties,heat resistance,mechanical properties,water resistance and flame retardancy of transparent flame retardant PCU films were characterized and analyzed by FTIR,TGA,SEM,transmittance test,mechanical property test,static water contact angle test,limiting oxygen index test and vertical burning test.The flame-retardant mechanism of CAPP flame retardant was discussed.The results shown that the combination of ultra-fine treatment and amino silane coupling agent modification technology can effectively improve the thermal stability and hydrophobicity of CAPP and the compatibility with PCU.When compound flame retardant was added,expanded carbon layer formed during combustion,which greatly improved the flame-retardant performance of transparent RPCU films and reduced the dosage of flame retardant.Especially,the compound flame retardant solved the problem of easy dropping of polyurethane material,and improves the mechanical property and thermal stability of RPCU films.The flame-retardant process is the cross-coexisted flame retardant of gas phase and condensed phase.