Synthesis and Linear and Nonlinear Melt Rheology of Well-Defined Comb Architectures of PS and PpMS with a Low and Controlled Degree of Long-Chain Branching
Synthesis and Linear and Nonlinear Melt Rheology of Well-Defined Comb Architectures of PS and PpMS with a Low and Controlled Degree of Long-Chain Branching
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DOI：
10.1021/ma302033g
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发表时间：
2013-06-25
期刊：
影响因子：
5.5
通讯作者：
Wilhelm, Manfred
中科院分区：
文献类型：
--
作者：
Kempf, Michael;Ahirwal, Deepak;Wilhelm, Manfred
合成了在线性和非线性变形下具有不同支化数目和支化长度的明确的单分散均聚物梳状结构，并研究了支化对不同流变性质的影响。流变学性质与梳状拓扑的相关性对于确定支化度具有特殊的意义。因此，合成了具有系统变化的支化数量和分子量、窄的多分散性以及可控制但较低的支化数量(通常为每个主干0.1-1摩尔96个支化)的明确的聚苯乙烯基梳状聚合物，并将其与Roovers系列中具有更多支化数量(每个主干1个摩尔96个支化)的聚苯乙烯梳子的数据进行了比较。为了详细研究其流变特性，采用了各种线性和非线性技术。在线性范围内，使用简化的van Gurp-Palman图(增量与垂直条G*垂直条/G(N)(0))来确定临界点，该临界点说明了支链相对分子质量和支链数目对所得流变性质的影响。在非线性区域，通过大振幅振荡剪切(LAOS)测量，由FT-流变学的二次标度律得到了非线性参数Q(0)(Omega)。基于Q(0)(Omega)参数的本征非线性主曲线反映了松弛层次，是一种在不同松弛时间尺度上提取信息的敏感方法。非线性剪切测量被单轴拉伸测量补充，以量化应变硬化效应以及分支松弛对应变硬化的影响。单轴拉伸测量的结果可以与由本征非线性主曲线Q(0)(Omega)获得的驰豫时间相关联。POM-POM本构模型的预测结果与拉伸流变学的实验数据进行了比较，重点关注了应变硬化行为，并对老挝进行了预测，重点考虑了非线性参数Q(0)(Omega)作为POM-POM分子中支链数目和相对分子质量增加的函数。通过对所应用的流变学方法(1)线性区域的小幅度振荡剪切(SAOS)，(2)LAOS结合FT-流变学，以及(3)非线性区域的拉伸流变学的比较，说明了每种技术在研究稀有但缠绕的支化梳状聚合物拓扑结构方面的检测极限和优缺点。
Well-defined, monodisperse homopolymer comb architectures with varied number and length of the branches under linear and nonlinear deformation were synthesized and examined to determine the effect of branching on different rheological properties. The correlation of the theological properties with the comb topology is of special interest for the determination of the degree of branching. Therefore, well-defined polystyrene-based comb polymers with systematically varied number and molecular weight of the branches, narrow polydispersities, and a controlled, but low, number of branches (typically 0.1-1 mol 96 branches per backbone) were synthesized and compared with data from polystyrene combs of the Roovers series that have a higher number of branches (>1 mol 96 branches per backbone). To investigate the rheological properties in detail, various linear and nonlinear techniques were applied. Within the linear regime, the reduced van Gurp-Palmen plot (delta vs vertical bar G*vertical bar/G(N)(0)) was used to identify critical points that illustrated the influence of the branch molecular weight and number of branches on the resulting rheological properties. In the nonlinear regime large amplitude oscillatory shear (LAOS) measurements were performed to obtain the nonlinear parameter Q(0)(omega) via a quadratic scaling law from FT-rheology. An intrinsic nonlinear master curve based on the Q(0)(omega) parameter reflected the relaxation hierarchy and was shown to be a sensitive method to extract information on the different relaxation time scales. The nonlinear shear measurements were complemented by uniaxial extensional measurements to quantify the strain hardening effect and how the strain hardening was affected by branch relaxation. The results obtained from the uniaxial extensional measurements could be correlated to relaxation times obtained from the intrinsic nonlinear master curve Q(0)(omega). Pom-pom constitutive model predictions were performed for the comparison with experimental data for extensional rheology with focus on the strain hardening behavior and for LAOS with focus on the nonlinear parameter Q(0)(omega) as a function of increasing number and molecular weight of the branches in the pom-pom molecule. A comparison of the applied rheological methods (1) small amplitude oscillatory shear (SAOS) in the linear regime, (2) LAOS in combination with FT-rheology, and (3) extensional rheology in the nonlinear regime illustrated the detection limits as well as the advantages and disadvantages of each technique toward the investigation of rare, but entangled branched comb polymer topologies.