Study On The Synthesis Of New Type Polyurethane Chain Extender And Its Relationship With Polyurethane Properties

Thermoplastic polyurethane(TPU)has excellent mechanical strength,wear resistance and reproducibility,and has been applied in many fields.TPU is a material with a micro-phase separation structure composed of soft and hard segments.The type and content of hard segments are one of the key factors affecting its mechanical properties and heat resistance.Chain extender is an important part of TPU hard segment,usually aliphatic diols such as butanediol are used.In order to obtain high mechanical properties and heat resistance,it is generally necessary to have a strong rigid segment and a high content of hard segments,so it can only be achieved by increasing the rigidity and dosage of isocyanate.Isocyanate is highly toxic,and increasing its dosage will result in uneven hard segment size.In this thesis,firstly,a glycol chain extender containing carbamate functional group was designed and synthesized,then use the new chain extender to increase the content of carbamate functional groups in the hard segment so as to achieve better performance without increasing the amount of isocyanate.The main work content is divided into the following two parts:(1)Using ethylene carbonate and diamines with different carbon chain lengths as raw materials,three new chain extenders with carbamate groups on the main chain,hydroxyl end groups and different numbers of methylene functional groups were synthesized by ring-opening reactions,Bis(2-hydroxyethyl)butane-1,4-dicarbamate(BHB),Bis(2-hydroxyethyl)hexane-1,6-dicarbamate(BHH),Bis(2-hydroxyethyl)octane-1,8-dicarbamate(BHO).Their structure were characterized by FT-IR and 1HNMR,and its molecular structure was confirmed.Thermoplastic polyurethane elastomers were synthesized using three new synthetic chain extenders,hexamethylene diisocyanate(HDI)and polytetramethylene ether glycol(PTMG).Compared with the performance of TPU synthesized with traditional chain extender BDO under the same hard segment,the results show that the TPU synthesized by the new chain extender has higher hydrogen bonding degree,more obvious microphase separation,lower glass transition temperature,higher softening point and higher mechanical strength.Among them,the softening point of TPU synthesized by BHH(163.87?)is 38.97%higher than that of BDO-TPU(117.97?),and the tensile strength of TPU synthesized by BHO reaches 31.5 MPa,which is 70.27%higher than that of BDO-TPU(18.5 MPa).(2)Using PTMG as the soft segment,self-made chain extender BHH reacts with different kinds of diisocyanates to synthesize TPU,Explore the influence of different isocyanate types and different hard segment content on the structure and performance of TPU.The study found that the TPU synthesized by BHH and HDI has the highest degree of hydrogen bonding,while its glass transition temperature is the lowest,the softening point is higher,and the mechanical properties are better.When the hard segment content increases from 33%to 43%,the hydrogen bonding degree of BHH-TPU also increases,the softening point temperature increases,the elongation at break decreases,and the tensile strength increases.