The shear and elongational rheology of linear and pom-pom shaped polystyrene (PS) blends was investigated experimentally and modeled using constitutive models such as the Doi–Edwards and the molecular stress function (MSF) model. The pom-pom molecule is the simplest topology to combine shear thinning with strain hardening in elongational flow. A PS pom-pom with a self-entangled backbone (M_w,bb= 280 kg mol⁻¹) and 22 entangled sidearms (M_w,a = 22 kg mol⁻¹) at each star was blended with two linear PS with weight average molecular weights of M_w = 43 and 90 kg mol⁻¹ and low polydispersities (Ð < 1.05). A semilogarithmic relationship between the weight content of the pom-pom, ϕ_pom-pom, and the zero-shear viscosity was found. Whereas the pure pom-pom has in uniaxial elongational flow at T = 160 °C strain hardening factors (SHFs) of SHF ≈100, similar values can be found in blends with up to ϕ_pom-pom = 50 wt. % in linear PS43k and PS90k. By blending only 2 wt. % pom-pom with linear PS43k, SHF = 10 can still be observed. Furthermore, above ϕ_pom-pom = 5–10 wt. %, the uniaxial extensional behavior can be well-described with the MSF model with a single parameter set for each linear PS matrix. The results show that the relationship between shear and elongational melt behavior, i.e., zero-shear viscosity and SHF, can be uncoupled and customized tuned by blending linear and pom-pom shaped polymers and very straightforwardly predicted theoretically. This underlines also the possible application of well-designed branched polymers as additives in recycling.

中文翻译：

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共混物中的复杂聚合物拓扑结构：线性/pom-pom 聚苯乙烯共混物的剪切和拉伸流变学

对线性和绒球形聚苯乙烯 (PS) 共混物的剪切和拉伸流变学进行了实验研究，并使用本构模型（例如 Doi–Edwards 和分子应力函数 (MSF) 模型）进行了建模。pom-pom 分子是在拉伸流动中结合剪切稀化和应变硬化的最简单的拓扑结构。一个在每颗星上具有自缠结主链（M _w,bb = 280 kg mol ^-1）和 22 个纠缠侧臂（M _w,a  = 22 kg mol ^-1）的 PS pom-pom 与两个具有重量的线性 PS 混合M _w  = 43 和 90 kg mol ^-1的平均分子量和低多分散性 (- < 1.05)。绒球重量含量之间的半对数关系，φ_pom-pom，并发现零剪切粘度。虽然纯 pom-pom 在 T = 160 °C 的单轴拉伸流动中具有 SHF ≈ 100 的应变硬化因子 (SHF)，但在高达 ϕ pom-pom = 50 wt 的混合物中可以找到类似的_值 。线性 PS43k 和 PS90k 中的 %。通过仅混合 2 重量。% pom-pom 与线性 PS43k，SHF = 10 仍然可以观察到。此外，在 ϕ _{pom-pom以上} = 5–10 重量。%，单轴拉伸行为可以用 MSF 模型很好地描述，每个线性 PS 矩阵都有一个参数集。结果表明，剪切和拉伸熔体行为之间的关系，即零剪切粘度和 SHF，可以通过混合线性和 pom-pom 形状的聚合物来解耦和定制调整，并且在理论上非常直接地预测。这也强调了精心设计的支化聚合物作为回收添加剂的可能应用。