Preparation And Properties Of Polyurethane Elastomers

Polyurethane elastomer(PUE)is widely used in various fields because of its excellent performance.With the rapid development of polyurethane industry,it also requires PUE has higher performance.Like other materials,the properties of PUE are inseparable from their versatile and special structures.Therefore,it is crucial to master the relationship between structure and properties for the further development and application of polyurethane materials.Based on the high cis-1,4 content terminated hydroxyl polybutadiene(HTPB)based polyurethane elastomer,the effects of soft segment and hard segment structure on the properties of elastomers were investigated in order to obtain a more comprehensive data and extend the range of applications of HTPB based polyurethane elastomersFirstly,4,4'-diphenylmethane diisocyanate(MDI)and 1,4-butanediol(BDO)were used as hard segments to compare the properties of PUEs with different soft segments:polytetrahydrofuran diol(PTMG),polycaprolactone diol(PCL),HTPB and free-radically polymerized hydroxyl terminated polybutadiene(FHTPB).It has been found that the toughness,rigidity and elasticity at low temperature(-30?)were better than room temperature(25?),which was attributable to the improvement of the degree of crystallization of the soft segment and microphase separation between soft and hard segments.Also,the elongation at break of HTPB-PUE was better than that the other three elastomers at two conditions,and the elastic recovery ability at-30? was also the best,but the mechanical strength was lower.The glass transition temperature(Tg)of HTPB-PUE was-103.3?(DSC),which was about 20? lower than PTMG-PUE and FHTPB-PUE and 60? lower than PCL-PUE.This can be attributed to the higher regularity of the HTPB structure resulting in a high degree of microphase separation of the elastomer.However,since the HTPB molecular structure does not contain polar groups,the hydrogen bonding force is weak,so the thermal stability was inferior to the other three elastomersNext,in order to improve the poor mechanical strength and thermal stability of HTPB-PUE,PCL was added into HTPB by physical blending as soft segment to synthesize a series of polyurethane elastomers with MDI and BDO,and the effects of different HTPB/PCL ratios on the properties of the materials were investigated.It has been found that the addition of PCL effectively increased the number of hydrogen bonds and the intermolecular force,thereby improving the mechanical strength and thermal stability of the elastomers.However,the elongation at break and the degree of microphase separation decreased as the PCL content increased.When the ratio of the HTPB/PCL was 1:1,the mechanical properties of the elastomer at room and low temperature were relatively good.At this time,the elastomer had two glass transition points at-102? and-43.8?(DSC),corresponding to two soft segment structures.Finally,HTPB was still used as the soft segment,and BDO was the chain extender.The effects of hard segment parameters on the properties of the elastomer were investigated.Firstly,MDI was used to react with HTPB and BDO to study the effects of different hard segment contents.Then,the effects of MDI,toluene diisocyanate(TDI),hexamethylene diisocyanate(HDI)and isophorone diisocyanate(IPDI)were compared with the same hard segment content.It has been found that the increase in the content of the hard segment resulted in a high degree of hydrogen bonding and microphase separation.This in turn increased the rigidity and strength of the elastomer,but the elongation at break decreased.At the same time,the low temperature resistance and thermal stability were improved,but the change was small.MDI and TDI made the materials have the highest tensile strength and modulus.The elastomer with IPDI had the highest elongation at break more than 600%.Due to the structural symmetry of the aliphatic HDI,HPU25 had the lowest Tg(-104 C)and the highest initial decomposition temperature(244 C).In general,the hard segment structure had greater impacts on the mechanical properties,while the thermal properties had less impacts.