Synthesize Thermoplastic Polyurethane Based On Isocyanate Blocked Reaction And Study Its Properties

Thermoplastic polyurethane(TPU)has been widely used in many fields for its excellent performances,such as high strength,good wear resistance,adjustable performance and synthesis process is simple;besides,it also has the advantages of thermoplastic material.The linear structure of TPU makes it have the properties of secondary processing,but it also has a noticeable defect,the mechanical properties are reduced after processing.Usually,TPU processing temperature at 170??220?,the-NHCOO-group will decompose when the themperature is above 200 ?.So that the TPU molecular chain will break in the process of machining,causes the lower molecular weight,and affects the mechanical properties.In practical application,we hope that TPU has better processing performance,and also hope that it can avoid the decrease of molecular weight and the mechanical performance.How to solve this problem is the key to expand the application range of thermoplastic polyurethane materials.Through thermal reversible characteristics of isocyanate blocking at low temperature and deblocking at high temperature,based on the research of laboratory,the bisphenol compound substituted by halogen was used as chain extenders to synthesize a kind of thermal reversible thermoplastic polyurethane and the thermal reversible temperature below the broken bond temperature of common carbamate.The TPU can occur deblocking reaction at high temperature,which can reduce chain length,improve processing liquidity and reduce processing temperature.When the temperature returns to room temperature,the deblocked isocyanate and phenolic hydroxyl group can react again,thus it can restore certain mechanical properties.In addition,the introduction of halogen also makes TPU have certain flame retardant properties.The specific research contents and results are as follows:(1)TCBPA?TBBPA and BPA as blocked agent,to react with MDI and synthesized three different blocked model compounds.By using FT-IR,1HNMR and GPC,studied the deblocking process of blocked model compounds.Besides,FT-IR and DSC methods to study the deblocking behaviours of different blocked compounds,the FT-IR results showed that TCBPA has the highest deblocking efficiency and degree;heating 30min at 160?,the deblocking degree is 66%,and DSC results showed that deblocking process absorbed the largest heat,which is 18.54J/g.(2)The thermoplastic polyurethane was synthesized by using TCBPA as chain extender.Using FT-IR tracking,DSC and TGA methods to study the deblocking behaviours,confirmed PU-TCBPA could occur the deblocking reaction at heating conditions.But,the deblocking degree was lower than TCBPA blocked MDI product.In addition,the dynamic analysis was performed by using the FT-IR datas of PU-TCBPA,it was found that the deblocking rate constant increased with the increase of heating temperature,and the activation energy is 35.2 kJ/mol.IR and DSC results also showed that the initial deblocking temperature is about 90? and 85 ? respectively.(3)Using FT-IR,DSC and GPC to investigate the thermal reversible behaviors of PU-TCBPA.FT-IR results showed that the blocking reaction could occur at room temperature after heat treatment.The deblocking and blocking of cyclic heating and cooling showed that PU-TCBPA has the thermal reversible behaviors.The results of DSC and GPC also showed the reversible behaviors of TPU.(4)The processing,mechanics and flame retardant properties of PU-TCBPA were studied by melt index,tension machine and oxygen index instrument.Melt index results showed that deblocking can give thermoplastic polyurethane a good processing performance.Tensile tests showed that mechanical strength can be restored to 80%after the first reversible heat treatment.The oxygen index test obtained the data is 27.1,showed that PU-TCBPA has good flame retardant performance.