【作者】 王万杰；

【导师】 郑强；

【作者基本信息】 浙江大学 ， 材料学， 2006， 博士

【摘要】 苯乙烯类嵌段共聚物作为一类重要的热塑性弹性体,广泛地被应用于汽车部件及工具手柄、电线电缆包皮或绝缘带、医疗制品及食品容器、密封胶、粘合剂、涂料以及聚合物共混改性等领域。对上述应用目标而言,黏弹行为不仅影响制品的加工性能,而且是决定制品最终性能的重要的因素之一。 本文选择四种苯乙烯类嵌段共聚物作为研究对象,系统考察了其线性、非线性黏弹行为以及热流变行为。鉴于它们在聚合物合金方面的广泛应用,还考察了尼龙/弹性体共混合金的线性和非线性黏弹行为。 动态应变扫描的结果表明四种嵌段共聚物的临界剪切应变(γ_c)的变化规律为,γ_c(SBS791)≈γ_c(SBS796)>γ_c(SEEPS)>γ_c(SEBS)。首次发现SEBS和SBS796嵌段共聚物的动态损耗模量(G”)～γ曲线中,在γ=24%和γ=61%处呈现最大值,这种现象与粒子填充橡胶体系相似。我们认为,当PS相区的尺寸与填充橡胶中的无机粒子尺寸在相同数量级时,嵌段共聚物的交联网络结构发生了类似于填充橡胶中填料网络的变化,这从SBS796的TEM照片得到了证实。动态时间扫描发现,动态应变扫描破坏的样品结构随着时间延长逐渐修复。 除SEBS嵌段共聚物外,其它三种嵌段共聚物均可从不同温度的动态频率(ω)扫描得到较宽ω的主曲线。分别用WLF方程和Arrhenius方程对移动因子(α_T)随温度的变化进行了模拟,得到了SEEPS和SBS的黏流活化能。基于不同温度的logG’～logG”曲线,考察了温度对嵌段共聚物微结构的影响,发现由于存在微相分离结构,嵌段共聚物的主曲线与均聚物不同,不是一条直线,而是一条在高ω区域上翘的曲线。此外,从动态损耗正切(tan δ)的最小值和交叉模量分别计算得到四种嵌段共聚物的平台模量和缠结分子量。长时应力松弛曲线证实了嵌段共聚物复杂的松弛行为,并从这些松弛曲线计算得到了四种嵌段共聚物的松弛时间谱。修正的BSW模型可以很好地模拟得到松弛时间谱,得到四种嵌段共聚物的最长松弛时间。 对四种嵌段共聚物的非线性黏弹行为进行了研究,并用Wagner模型对非线性黏弹行为进行了预测。结果表明,四种嵌段共聚物的线性松弛行为可用更多还原

【Abstract】 As a kind of popular thermoplastic elastomers, the styrene block copolymer has been widely applied in many fields, such as automobile parts, toolholders, casings of electrical wire and cable, medical appliances, food containers, encapsulant, adhesive, coating, polymer blend materials. It is well-known that viscoelasticity is an important factor to determine processing and ultimate properties for polymeric materials, especially for block copolymers. In this dissertation, we choose four styrene block copolymers as models to investigate their linear and nonlinear viscoelastic behaviors and thermorheological behaviors. On the other hand, we also investigate the linear and nonlinear viscoelastic behavior of nylon / elastomer blends in view of their having extensive widely applications.From the dynamic strain sweep test, the critical shear strains (γ_c) of four block copolymers have been determined. The results show the following ranks as y_c(sBS791) ~ γ_c(sbs796) > γ_c(seeps) > γ_c(sebs). It is found that SEBS and SBS796 block copolymers exhibit peaks in the dynamic loss modulus (G’) ~frequency (ω) curves at γ = 24 % and γ = 61 %, respectively. These phenomena are similar to that of the rubber system filled with inorganic particles. We believe that cross linking networks of block copolymers have the similar change with the networks in filled rubber systems when the dimensions of PS phase is in the same level with those of inorganic particles, which has been conformed by the TEM micrograph of SBS796. The curves of dynamic time sweep test indicate that the structure of samples destroyed by the cumulating shear strain is repairable repair gradually with increase of time.Except SEBS block copolymer, the master curves of other three block copolymers with relatively large ω ranges were obtained from the curves of dynamic ω sweep based on time-temperature principal. It is found that WLF equation and Arrhenius equation can be applied to simulate the curves of shift factors (α_T) ~ (T) temperature well, and the fluid activation energy of SEEPS and SBS block copolymers can be obtained. The examination of the effects of temperature on the microstructures ofblock copolymers based on the curves of logG’ vs. logG" shows that the master curves is not a straight line but a curves with upturn in the high ? because of the micro-phase separation structures. In addition, the plateau modulus and the entanglement molecular weight were calculated from the minimum of tan8 and cross modulus (Gc). The long time relaxation curves show the complex relaxation behaviors, from which the relaxation spectrums of block copolymers were calculated. A modified BSW model can be used to predict the spectrums well and obtain the longest relaxation times.The nonlinear viscoelastic behavior of block copolymer were investigated and simulated by a nonlinear Wagner model. The results show that the linear relaxation behaviors of block copolymer can be evaluated by the Maxwell model, and the predictions give the characteristic relaxation time and corresponding modulus of different relaxation modes. Moreover, it is found that melts of block copolymer follows the time-strain separation principle and the damping functions of block copolymer calculated from nonlinear relaxation modulus can be simulated well by Wagner function, Soskey-Winter function, Laun function and Papanastasiou function. In additon, the successive start-up of shear behavior, the steady-up shear behavior and the relaxation of steady-up shear behavior are investigated, respectively. The results show that Wagner model, derived from the K-BKZ (Kearsley-Bernstein, Kearsley, Zapas) constitutive equation, can simulate the experiment data of SEEPS block copolymers well, but underpredict the nonlinear viscoealstic behaviors of SEBS block copolymer and overpredict the nonlinear viscoelastic behaviors of SBS. The reason for failure is believed to be that the damping functions obtained are not precise.The studies on the thermorheological behavior of block copolymer demonstrate that block copolymers are thermorheological complex materials. From the co corresponding to maximum of tan5 and Gc, the mean relaxation times of segmental relaxation process and terminal relaxation process were calculated. The VTF function was used to predict the curves of mean relaxation time and a satisfactory prediction was obtained. It is known from analysis of parameters in VTF function that VTF function is unsuitable to describe the segmental relaxation behaviors of blockcopolymers but can describe the terminal relaxation behavior well.The results from dynamic temperature sweep torsion test show that the glass transition temperature (T%) of PS block is lower than that PS homopolymer, and a shoulder peak appears at 115°C, which is perhaps the relaxation behavior of polystyrene macromolecular chains under the effect of interaction between hard block and soft block. The results from dynamic temperature sweep in parallel plate mode show that when the shear strain is low, the curves of viscoelastic parameters ~ T have relatively finely symmetrical, which demonstrates that shear strain don’t destroy the structures of sample but induce the structures to be perfect in the process of temperature circulation. When the shear strain is high, the structure breakdowns and the obvious repaired process of structures also can be observed.Studies on the linear viscoelastic behavior of nylonl212 toughened with SEEPS (styrene-[ethylene- (ethylene-propylene)]-styrene block copolymer) elastomer were carried out. For the virgin polymers, the complex viscosity of nylonl212 increases as the (o decreases and approaches a constant at the low a, exhibiting a behavior of Newtonian fluid;while for SEEPS elastomer no Newtonian plateau appears in the (o observed. For the blends, curves of G’~a> are located between those of virgin nylon and SEEPS within o> range measured, and the G’ of blends increase with the content of SEEPS increasing and show self-similarity viscoelastic behavior. Furthermore, Palierne emulsion model was used to describe the viscoelastic behaviors of blends. The results of prediction show that it is not decent to describing the viscoelastic behaviors of the double phase system toughened with elastomer, especially for the high content of elastomer.The positive deviation observed in the plot of C versus blend composition shows that the blends are immiscible. From the point of phase transition, the phase-inversion region for these blends was predicted to be in the range of 30 % ~ 50 % weight fractions of SEEPS, which agrees with the morphology analysis of nylonl212 / SEEPS blends. Furthermore, it can be found that from the curves of G*(co) ~ r/*(a>) that the blends don’t exhibit stress yield behavior but SEEPS elastomer show the character of stress yield behavior. However, the cole-cole plots of modulus show thatthe microstructures of blends are unstable in the phase transition region. In addition, the weighted relaxation spectrums were calculated based on the Schwarzl and Staverman differential equation and present the particular relaxation behavior of virgin polymers and their blends.The nonlinear Wagner model can give a satisfactory prediction of nonlinear viscoelastic behaviors for virgin nylonl212 and their blends with SEEPS (90 / 10), but cannot predict the nonlinear viscoelastic behaviors of other blends with high content of SEEPS. Studies on the thermorheological behaviors of blends show that modulus is sensitive to temperature in the melting and crystal processes.更多还原