磺化SBR离子聚合体的熔融行为及力学性能

MELT FLOW AND MECHANICAL PROPERTIES OF SULFONATED SBR IONOMERS

将自制的磺化丁苯橡胶离子聚合体(简称离聚体)与增塑剂硬脂酸锌在Brabender塑性仪密炼机中混炼,并热压成型,考察了制备条件及增塑剂用量对平衡扭矩(190℃)、粘流活化能及物理机械性能的影响.结果表明,当增塑剂用量为26％(质量),磺化度为0.35meq SO_3H/g胶,中和度为2.0时。镁离聚体是一种很好的热塑性橡胶,可在160～190℃加工,拉伸强度大于17 MPa,扯断伸长率大于600％,永久变形小于50％。用不同金属离子中和的离聚体的熔融粘度依下列次序递减:Li^+U,Na^+,K^+;Mg^(2+),Pb^(2+),Pb^(2+),Ca^(2+)。其拉伸强度依下列次序递减:Li^+,Na^+,K^+,ph^(2+),Zh^(2+),Ca^(2+),Mg^(2+)。

The highly unsaturated butadiene - styrene rubber ( SBR) was sulfonated in high concentration and SBR ionomers were prepared by neutralization . The melt flow and mechanical properties of sulfonated SBR ionomers were investigated in Brabender Plasticorder .The ionomers alone could not be kneaded uniformly together and could not be compression molded well even at 190°C due to the strong association of the sulfonated groups . However , with addition of zinc stearate as ionic plasticizer , the mixing torque value which represents the melt viscosity of the ionomer decreases obviously . With increasing amount of zinc stearate , melt viscosity of the ionomer decreases while flow free energy (ΔE) increases slightly (Figure). This is because zinc stearate is distributed in the ionic domains of the ionomer , the carboxylic salts exchange with sulfonic salts of the ionomer , resulting in weakening the ionic association and diminishing the size of the ionic domains and increasing the number of domains . With increase of sulfonation degree , both the melt viscosity and ΔE increase . It is obvious that the increase of ionic groups raises the ionic crosslink density or association degree . In the case of neutralization degree below 1.0 melt viscosity and ΔE increase with neutralization degree , while excess neutralization nearly exerts no influence on them . The melt viscosity of ionomers neutralizedwith different metallic ions decreases in the following order :Li+,Na+ ,K+;Mg2+,Zn2+,Pb2+, Ca2+. This almost implies that the higher the ionic potential , the stronger the attraction between acidic groups and cations , and the higher the melt viscosity .Zinc stearate can enhance both the tensile strength and ultimate elongation of the ionomer , keeping the permanent set almost unchanged . This effect is probably due to that zinc stearate is distributed in the ionic domains , reducing the interaction between sulfonic salts , decreasing the ionic domain size and making the distribution of ionic domains more uniform , resulting in decrease of local stresses concentration . Zinc stearate also makes the ion exchange more easily , thus increasing the ultimate elongation . With increase of sulfonation degree tensile strength of the ionomer increases while its ultimate elongation decrease . It is simply due to the increase of ionic groups and the crosslink density . When neutralization degree increases from 0.9 to 1.0, tensile strength increases markedly . This is because the electrostatic attraction between the sulfonic salts is stronger than the hydrogen bond interaction . Excess neutralization shows almost no effect on the mechanical properties .lonomers neutralized with different metallic ions exhibit tensile strength decreasing in the following order :Li+,Na+,K*; Pb2+,Zn2+,Ca2+,Mg2+(Table) .It indicates that tensile strength of the ionomers neutralized with univalent cations decreases with decrease of ionic potential while that of the ionomers neutralized with divalent cations decrease with increase of ionic potential . This may be explained by the fact that univalent cations form weak crosslinks through association of opposite charged ions ,while divalent cations form strong crosslink through ionic bonds. For univalent cations the higher the ionic potential ,the larger the repulsive force between the cations , and the more dispersed the ionic domains and therefore the greater the strength of the ionomer . For divalent cations the higher the ionic potential of a metallic cation ,the larger the electrostatic attraction between cationsand acidic groups and the less probably the cations exchange and hence local stresses can not be eliminated . The existence of external d- level electrons makes Zn2+ more covalent and it is easier to interchange their ionic bonds . When stress was applied to the zinc ionomer ,cation exchange between neighboring groups through dissociation and reformation of ionic bonds may occur so as to prevent the formation of local stresses and hence premature failure .Most ionomers can be processed at 160 - 190########C an