Preparation And Properties Of Heat-resistant Thermoplastic Polyurethane Elastomers

The thermoplastic polyurethane elastomer(TPU)is an(AB)n type of linear block polymer.There are many hydrogen bonds formed by physical crosslinks between the molecular chains,which are soluble and meltable.It has excellent properties such as high modulus,high strength,excellent wear resistance,and is easy to process.The waste material can be recycled and reused.However,the low heat resistance of TPU limits its application in the high temperature field.At present,the ordinary TPU can be used only at 80? for long time,and if used at 120?,it can only persist for a very short time.Sothat,it cannot meet the application requirements of some special fields In this dissertation,the TPU chain extender,hard segment,and soft segment are modified to obtain high temperature resistant TPU with excellent mechanical properties and thermal properties.The main results of this paper include:(1)A series of thermoplastic polyurethane elastomers(TPUs)with polytetrahydrofuran diol(PTMG-2000)soft segment and different types and contents of hard segments were prepared by using the pre-polymer method.The types of hard segments examined were the reaction product of 4,4'-diphenylmethane diisocyanate(MDI)respectively with four different chain extenders,i.e.1,2,4,5-benzenetetracarboxylic dianhydride(PMDA),3,3',4,4'-benzophenonetetracarboxylic anhydride(BTDA),3,3',4,4'-biphenyltetracarboxylic dianhydride(BPDA)and 1,4-butane alcohol(BDO).These TPUs' thermal and mechanical properties were investigated.The results showed that introduction of the aryl-imide groups improved the initial decomposition temperature of the TPUs.The initial decomposition temperature of TPU with BPDA-MDI hard segment is about 350?,which is better than TPUs respectively with BTDA-MDI and PMDA-MDI hard segments,and much higher than that of the conventional TPU with the BDO-MDI hard segment(270?)When the content of hard segment is 40 wt%,the hardness of the aryl-imide type TPUs is greater than 92A,the tensile strength is 36?40MPa,and the elongation at break is greater than 500%at 25?.All are higher than those of the TPU with BDO-MDI hard segment.Even at 80?,the aryl-imide type TPUs still have high Young modulus,tensile strength and elongation at break.Comparing with the TPU with 40wt%of BDO-MDI hard segment,the TPU with the same weight content of PBDA-MDI has 3.8 and 18 times of Young modulus,2.1 and 3.4 times of tensile strength,and 1.03 and 2.5 times of elongation at break respectively at 25? and 80?.Moreover,the elastic recovery ability of the aryl-imide type TPUs does not decrease although they have greater hardness and rigidity,which is slightly better than that of the TPU with BDO-MDI hard segment.Under the 100%strain condition,the elastic recovery rate is greater than 81%.(2)By synthesizing a series of oligomers of different degrees of polymerization under low temperature conditions,the hard segment has a certain length,and aryl-imide structure is introduced;the oligomer is reacted with PTMG-2000,A series of TPUs with block regularization were prepared(PI method).The results show that the introduction of aryl-imide groups can improve the thermal stability of TPU.The initial decomposition temperature of PTMG-PMDA-TPU is between 320? and 350?,which is higher than the conventional pre-pretreatment about 15?;The TPU sample showed a relatively obvious melting absorption peak in the range of 170? to 190?.The arrangement of the molecular segments was more regular,which promoted the aggregation and crystallization of the hard segments of the TPU and formed hard segment microdomains.Comparing with the TPU with 37wt%of PMDA-MDI hard segment of PMDA-37%,the TPU with the same weight content of PTMG-PMDA-37%has 3.8 and 18 times of Young modulus,2.1 and 3.4 times of tensile strength,and 1.03 and 2.5 times of elongation at break respectively at 25? and 80?.These are because the oligomer as a hard segment has a certain length,and the(AB)n block in the TPU chain is regular,which facilitates the aggregation of hard and soft phases and promotes microphase separation.In the synthesis of PI method,when the degree of polymerization of the oligomer is 2 or 3,the mechanical properties are both elastic and strong,hard and tough.(3)The high-cis-terminated hydroxyl-terminated polybutadiene was used as the raw material,and the oligomer synthesized by PMDA and MDI according to a certain ratio was used as the hard segment.The solution was synthesized by two-step method to synthesize HTPB-TPU.The amine group can improve the thermal stability of HTPB-TPU,and its initial decomposition temperature is about 350?,and the higher the relative molecular mass of the soft segment HTPB as the raw material,the better the heat resistance.DSC shows that HTPB has a glass transition temperature as low as-105? and has excellent low temperature flexibility.The HTPB-TPU can be used at lower temperatures,which broadens the limits of low temperature use.The mechanical properties of HTPB-TPU under different temperature conditions were tested.It was found that the structure of aryl-imide has greatly improved the mechanical strength of HTPB-TPU,The higher the HTPB molecular weight and the hard segment content of TPU,the better the heat resistance of the HTPB-TPU at higher temperatures,and the softer and elastic state at a lower temperature.When the soft segment of HTPB has a molecular weight of 3,500 and the hard segment content is 45%,the overall performance is optimal.HTPB-TPU is softer and remains elastic at-20?.HTPB-3500-45%-TPU still maintains 80.3%elastic recovery at 100%fixed strain.