Preparation Of Branched Polyurethane-Urea Elastomer And Relation Microphase Separation With Electromechanical Properties

Polyurethane elastomers are electroactive polymers capable of producing a variety of mechanical responses,such as bending,expansion,and contraction,under the influence of external electric fields.Due to its exceptional properties,polyurethane elastomers have important applications in various fields such as flexible electronics,soft robots,smart vehicles,and intelligent healthcare.However,the unclear mechanism of microphase separation and high modulus of polyurethane elastomers limit the improvement of their electro-responsive performance.This study focuses on the modulation of the polyurethane-urea elastomer network structure in a rational way.To achieve this,multiple-arm structure extenders were introduced to control the chain structure and optimize the physical and mechanical properties of the structure,including hysteresis loss,heat resistance,dielectric properties,and electro-bending actuation performance.Consequently,the research established the correlation between the microstructure and the electromechanical properties of the branched polyurethane-urea elastomer.The detailed contents of the research comprise the following:(1)the polyurethane-urea elastomer was synthesized using hydroxylterminated polybutadiene(HTPB)as the soft segment,isophorone diisocyanate(IPDI)and 4,4’-methylenebis(cyclohexylamine)(PACM)as the hard segments,and four-armed poly(ε-caprolactone)(PCL410)as the crosslinking extender,with different amounts of 0%,10%,20%,and 30% of PCL410.The effects of PCL410 contents on the microphase separation,mechanical properties,and electro-bending actuation performance,as well as the electro-bending actuation mechanism,were analyzed.The results indicated that an increase of PCL410 contents enhanced the tensile strength up to 3.61 MPa,elongation at break up to 1243%,decreased residual strain and hysteresis loss after multiple stretching cycles to 30.6%.This improvement occurred because the introduction of PCL410 increased the quantity of longbranched and cross-linked chains,thereby destroying the strong hydrogen bonding between the hard segments and leading to additional free carbonyl groups,which,in turn,increased the degree of microphase separation.The HTPB-PCL410-20 component had a regular distribution of hard segments and small molecular chain constraints,allowing it to exhibit the maximum electrobending displacement of 5.16 mm and bending actuation stress of 8.30 Pa,which was 74 and 76.3 times,respectively,greater than that of the HTPBPCL410-0 component under the nominal electric field of 180 V/μm.Moreover,the branched structure formed by PCL410 significantly improved the polyurethane-urea elastomer’s electro-responsive bending properties,whereby the polarization orientation of polar carbonyl dipoles and the dipole mutual interaction between adjacent carbonyl-C=Oδ-···+δC=O-enhanced the electro-responsive bending response under an electric field.(2)The present study investigated the impact of low-content crosslinking agents,namely,three-arm poly(ε-caprolactone)(PCL305)and four-arm poly(ε-caprolactone)(PCL410),on the microphase separation structure,mechanical properties,and electromechanical bending actuation performance of polyurethane-urea elastomers.The results exhibited that the addition of 5%multiblock crosslinking agents reduced the Young’s modulus to 1.07 MPa,while increasing the elongation at break to over 600% and the residual strain after multiple stretching cycles to a significant 51.7%.The observed changes were attributed to the formation of short branch chains in the main chain of the elastomer by the low content multi-arm crosslinking agents.This led to improved plasticization modification of the system’s free volume and limited energy dissipation of the elastomer network.Among the electro-bending actuation,PUUs-PCL410-5 boasted the best electro-bending performance,displaying a maximum bending displacement of 11.30 mm at a nominal electric field of 90 V/μm.This value was remarkably 59.5 times higher than that of the PUUs component.Moreover,the maximum bending angle of PUUs-PCL410-5 reached 36.99°.Additionally,the stability and durability under the electric field driving substantially enhanced in this configuration.